13:01:59 Cool. So, last time I spoke last week I was talking about know some ideas that we've been having about ways, of course greening microbial ecology by metabolism, in the sort of hopes that, you know, just as metabolism gives us enough constraints to understand
13:02:16 the large scale organization of microbial communities and sediment. Maybe they also tell us something about the dynamics. So, what today's whole talk about is to just take the opposite tack instead of averaging over many bacteria we're going to focus
13:02:30 on just one type of bacterium and try to understand something about it psychology and behavior.
13:02:36 So the general problem, just to set us up is, again, related to the formation of these ingredients. So here's the same microbial community that I was showing last week we've got the different metabolic players.
13:02:49 If you measure the action concentration is a function of death, you see that the action typically goes to zero, within about a millimeter. So the penetration depth of oxygen is around about 2 million.
13:03:00 these gradients that are extraordinarily dynamic, so if you compare the days and nights cycle. You can see that as the sun rises photosynthesis begins at the surface option penetrates down instead of going down one millimeter it's now going down two millimeters.
13:03:15 You can also imagine the title, the title cycle would also be important, depending on if it's low tide or high tide you might be underneath a quick moving stream or a stagnant pond.
13:03:29 So this is a constant stress for bacteria living in sediment. So every couple of hours you can imagine them needing to move several thousand body length vertically to avoid these action gradients, pushing down towards them, or if they're aerobic bacteria,
13:03:44 they need to move with these changing auction gradients. So they need to travel thousands of body lines every couple of hours in a specific direction that already is quite hard.
13:03:56 I think it's harder when you remember that they're in sediment. So not only do they need to move several thousand Bonnie vines to get to a safe place for them to live, to avoid, you know, either suffocating or burning to death as the as the chemical gradient
13:04:08 change. They need to navigate through elaborate and find pore space.
13:04:15 Jordan be standing up problem within the specific context of.
13:04:22 Oh, it's not far from random packing, so the guns, oh sorry yes, that the answer was, what is the typical porosity. So we've got probably dispersed and greens greens are typically about a millimeter.
13:04:34 So you've got sort of a 10th of a millimeter scale Porter's between sand grains and the absolute density is not far from random packed in 3d. So I think that's like 60, something percent.
13:04:47 I can't remember.
13:04:49 Yeah, absolutely. So if you sort of take a gross average.
13:04:58 You know, you get sort of 10th of a millimeter but of course you've got some wide, wide distribution about that.
13:05:04 So one of the things we want to do is just get one of these things into a into a micro CT, and just characterize this porous environment, so that's that's something we'll be doing this fall but now if you look up in textbooks, you get poor sizes that
13:05:18 are you know of order 100 micron but take some care with that.
13:05:23 So this is the microbe that we're going to be talking about today. And one of the funny thing, so there there are spiritual organisms, each one is about five microns in diameter.
13:05:33 And the funny thing about this thing is that this is not a bacterium, this is a colony of about 60 bacteria that are all attached to one another.
13:05:40 So, each one of these little green bumps is an individual bacterial cell within a spiritual microbial colony, their adult approach to bacteria and they need, and their most often found close the penetration up the box.
13:05:55 So, you can see their structure a little bit better and sem.
13:05:58 If you look you can see that the surfaces are a faceted each one of these facets is the surface of one particular cell cells within a colony growing divide the colony gets bigger.
13:06:11 Eventually it gets in one direction and then it buckles, and the whole thing divides symmetrical.
13:06:16 So this is one of the only known obviously multicellular bacteria.
13:06:21 They have. So these bacteria have never been found, living as individual cells, and it appears that the only way that they reproduce is within these comments.
13:06:30 Yes.
13:06:37 So if you look at them and cross section.
13:06:39 Yes, the question is what is the geometry of the other cells is that a three dimensional package or is it a two dimensional pack.
13:06:46 So if you look at them in a tm cross section, you can see that it's a model layer of cells, go through the surface. So, each individual sell.
13:06:57 So I've outlined one of them in this blue here.
13:06:58 So, each individual cell has some sort of pyramid shape.
13:07:02 This is of course the 3d packing of pyramid shapes. This is 11 cells in the circumference so about 60 cells coaching the surface.
13:07:10 And it's separating the inside, where you've got a little a cellular vacuum, and the outside so a monolayer cells, separating a sort of internal vacuum from the outside,
13:07:30 There are unicellular my ninja tactic bacteria The most common ones are magnetic spring them, so that I guess the one that most people work with. So there are a diverse assemblage of different magnetic tactic bacteria.
13:07:38 This specific type has only been ever has only ever been found and multicellular communities. There are attempts of people have made to break these out.
13:07:52 So you can add different detergents to sort of weaken bottom bounce between them.
13:07:57 Whenever they fall apart individual cells lose their membrane potential, it's sort of unclear if that's, you know, disintegrating is the first step of death, or if when you break them up they die instantly.
13:08:10 But in any case, nobody has ever seen these bacteria live, you you've never seen one of these little pyramid cells swimming all on its limbs. Yes, I was just wondering, given these are insanely cool, you started your talk by let's how to bacteria follow
13:08:25 gradients. Yeah, let's look at this one example or this is like super cool let's understand what these bugs do.
13:08:39 So for your own your path towards this question. Oh, okay.
13:08:41 Hey, what I'm going to answer that in the next two slides, and then we'll get back to the question.
13:08:44 So these things are pretty cool, as has been observed.
13:08:49 There are also some really fundamental questions about how they're able to do this. Oh, I'm sorry I didn't say anything about that last slide.
13:08:57 I'm sorry.
13:09:01 Ah, ok.
13:09:03 So the question is, are they found in both the northern hemisphere in the southern hemisphere. I'll mention that again in a few slides as well.
13:09:12 So, I've highlighted these little red rectangles here within these, you can see some little white dots. There's white dots are where the magnetism spelled out Magneto zones are magnetic particles that are precipitated by these cells.
13:09:26 They're either magnetite or Greek Aight, and so as each cell precipitates these magnetic particles, the entire colony has some net magnetic moment that will rotate passively to align with Earth's magnetic field.
13:09:42 Yeah, so the question is is do the buying homes align with one another. So people have done experiments to measure the net magnetic moment of one of these colonies, and then you can blast it with a really powerful magnetic field.
13:09:54 And you can measure the increase in the magnetic moment after you force them all to be aligned, and it changes by
13:10:04 by sort of a few percent. So if you figure out the alignment between them, based off of average everybody's aligned to a common direction to within about 20 degrees.
13:10:15 So it's very well done.
13:10:17 Nobody knows how it's done.
13:10:23 It gets more confusing when you start thinking about the flagella. So, each individual each individual sale within this colony has about 30 flagella.
13:10:33 And it seems that when they swim through the fluid, everybody is rotating their flesh out other all cooperating to move through the fluid.
13:10:42 This is sort of mysterious you can imagine that the colony is a whole.
13:10:46 Sorry, I don't think people on zoom can see me dance.
13:10:50 Okay, but I'll try to narrate as I go. So you can imagine that the magnetic moment points of some direction, and the Earth's magnetic field is going to pass if we turn that is going to.
13:11:05 So the organism is going to passively align with Earth's magnetic field. The whole trick to Magneto taxes. Is that all the cells need to coordinate their flagella to exert a net force that's parallel to their magnetic moment.
13:11:16 This is sort of easy to do with your unicellular organism.
13:11:20 because you can imagine you know you just precipitate your magnetism in one direction, you stick all of your full gel on either one side or the other, and then automatically the force you exert is parallel to your magnetic moment.
13:11:32 If you are multicellular bacteria, the geometry of the entire cluster is changing over the multicellular growth cycle. So somehow the cells need to keep track of.
13:11:43 Are they in the front, are they in the northern hemisphere of this colony need to pull. Are they in the southern hemisphere need to push. Nobody knows how that stuff.
13:11:53 So Michael asked a question of I want to study the gradient. And this is a super cool bacteria that does this.
13:12:00 If I'm being brutally honest with you, I got attracted this bacteria based off of all the questions of how do you know, understanding the evolution of multicellular Verity through the ways that these different organisms coordinate to move as a as a colony.
13:12:15 I don't have much interesting to say about that today.
13:12:19 But I do have some interesting things to say about how they move, how they navigate through a course space.
13:12:25 So we just got a grant funded I heard a rumor to study these things in more detail so keep, keep posted. I'll keep you posted.
13:12:33 So, there was also a question of do these things appear across across the entire globe. So, the sort of idea that people give behind fact data taxes, is if you think about the Redux gradient.
13:12:47 If you're in the sediment, as you go up, You're moving towards more oxygen.
13:12:53 If you measure Earth's magnetic field I've got a terrible sense of direction, but let's say it's in this direction. If you're at the equator, and you take a three dimensional compass, you know, North is perpendicular to the surface of the earth.
13:13:06 The further you go north.
13:13:08 If you're standing at the magnetic north pole North a straight down.
13:13:11 So more of us, the angle between perpendicular to the earth and the actual magnetic field is not far from your latitude.
13:13:22 So in Massachusetts there's a substantial magnetic component that's pointed opposite the direction of the radar screen. So swimming north is the same as swimming down.
13:13:31 This makes a strong. This makes a strong prediction that in the Northern Hemisphere things should avoid oxygen by swimming north in the southern hemisphere, they should swim south, and nobody should live at the equator.
13:13:44 Right, because at the equator there's no benefit to us. So in the Northern Hemisphere, most things swim north and the southern hemisphere most things swim South it's not 100%, there is an interesting question of, is that we don't understand something,
13:13:57 or is that,
13:14:01 or is that just a sort of sloppiness of magnitude taxes, and they totally live at the equator.
13:14:08 So, clearly we're missing something, Sergei may be unrelated question you call it magnetic Texas in my mind magnetic axis if you swim up the gradient and magnetic field.
13:14:19 Yeah, but you are referring to just swimming in the direction of the magnetic so am I right, you are defining magnetic taxes on a totally sensible way, that is different from the way that everybody else defines that got it.
13:14:31 Everybody else defines it as you swim parallel to magnetic field lines, your question.
13:14:41 Yeah.
13:14:48 so the question was about.
13:14:51 To what extent.
13:14:52 You know in the Northern Hemisphere I said most swim north.
13:14:56 The fraction or seeking and self, seeking that you measure when you look under a sample.
13:15:08 That's how people estimate. So basically it's you take themselves out of a bucket you put them under a microscope, you look at the fracking that's going north and the fraction that swim south, that fraction changes in time, and it also changes with how
13:15:18 you enrich it. So I think that some of that variability is just as confusing the bacteria as we take them out of their environment.
13:15:24 All right, so there's a bunch of interesting questions and I would love to have more interesting things to say about them. I'm happy to speculate. But I don't want to do that again.
13:15:33 So we can speculate at the barbecue if you're interested.
13:15:38 So if we're thinking about how these things move through their three dimensional environment through this Porter space. Now I've drawn these Porter's grotesquely exaggerated just to make things easier to easier to illustrate, there are two important torques
13:15:51 that guy these bacteria through the through the setup. The first one is the magnetic torque on the, on the bacterium. So the magnetic moment, times the magnetic field gives you the magnetic torque on the cell.
13:16:02 If you balance that with the viscosity and the size of the cell, you get the typical rate at which the magnetic field rotates the bacteria, the spherical bacterium through the viscous fluid.
13:16:15 Given that timescale in the speed of the cell you, that tells you how far the these bacterial colonies swim before they align with the field. So I'm going to call that l.
13:16:26 So that works pretty well, you can align with the magnetic field.
13:16:30 I haven't measured em yet in the talk, if you so we do measure em I'll show you that in a moment. But the typical length scale for for aligning with Earth's magnetic field is about 300 micron.
13:16:43 Do you swim about a third of the millimeter before you align with Earth's magnetic field. And that takes you know, a small number of seconds.
13:16:53 The issue with using this to navigate vertically through mud, is that if you swim due north, you invariably collide with a particle.
13:17:02 So once you once you get close to a part of who you need some way of getting away from you need some way of escaping that surface after you call it.
13:17:12 There are a bunch of different ways that you can do this but basically, all of these all the small scale torture games become important once the cell gets within about a body length of the, of the surface so the two important ones you can imagine, is
13:17:25 this I was swimming through the water it's pushing water out ahead of it. If it's swimming towards a hard surface there's no slip boundary condition. So as the cell pushes water into the surface, the surface pushes back on the cell that can exert forces
13:17:37 and works on the cell.
13:17:40 Yes. So we'll measure the rotational diffusion coefficient on the next slide.
13:17:44 So, you can also imagine that this entire thing is covered with with flagella, they can all bang into the surface.
13:17:53 We have some hope of understanding how a sphere rotates through, through a fluid close to a boundary, low Reynolds number.
13:18:02 The way that Fidelis interact with a boundary sort of an internet black hole into which we can throw all of our insertion.
13:18:09 I'll try to avoid doing that.
13:18:12 So the sort of idea behind the the experiment that we're talking about today are going to be that first line scale, L is something that I can control experimentally by varying the magnetic field.
13:18:23 So we've got these two different types of torques that act on the cell that act on the colony on two different scales, and I can tune the ratio others going skills by adjusting the magnetic field.
13:18:35 So let's start by just characterizing the emotion.
13:18:38 So if you write down how theta changes in time, it aligns with the magnetic field at some rate gamma, which is proportional to the magnetic field and the magnetic moment.
13:18:48 And then we've got some Brownian motion on top of that.
13:18:52 So, just to orient yourself, this little thing here that I circled in red. That's one colony.
13:18:58 I've got this entire thing in a three axis Helmholtz coil. So let me just start by projecting a 256 micro Tesla magnetic field directly up.
13:19:08 And then about halfway through the video, I mean to rotate it 90 degrees, it takes me about a millisecond to do that.
13:19:15 And you're going to see a blue arrow which is showing the average direction that the micro the colonies are swimming.
13:19:22 So let's look at that. So, We started off, everybody's swimming do upwards.
13:19:28 And now in just a moment I turned the field.
13:19:32 And we can see the colonies tending to align with that field.
13:19:41 It's an enormous amount of fun. To do this, and you can attract undergraduates like flies to Candy by just handing them a magnet and telling them to go while it's immensely satisfying.
13:19:55 Exactly, yes yes I have Magneto tactic tactic undergraduates.
13:20:02 Yeah, sure.
13:20:07 Just real quick. What is beta is that the change in direction. So, theta is the angle between the direction of motion, and the applied magnetic field of the magnetic torque is so is the magnetic moment cross with a magnetic field.
13:20:22 And so the right data changes is sort of the sign of the angle between the magnetic moment, and the and the applied field. I'll clarify I'm a microbiologist.
13:20:30 Okay, cool.
13:20:32 But so it's essentially it's the it's the change in angle of the magnetic field. So this is, so d theta DT that's how quickly you're rotating. Right, okay.
13:20:42 And the rate at which you're rotating is related to the sign of the angle between the direction your magnetic moment is pointing in the direction of the magnetic field is his point okay.
13:20:49 So if you're. Yeah. Cool. Thank you.
13:20:52 So, if we took the dynamics of that blue line at a variety of magnetic fields, and for each one we fit this parameter gamma. We got a nice collapse of the data for three different magnetic fields.
13:21:04 And so we can extract from this the magnetic moment of an average colony. You can of course do this fit for every colony individually to get the variability and magnetic moments between colonies, and they vary by by a factor of 30
13:21:27 other natural typical density in which they live. Okay, so two big caveats to this. The first one is, nobody can grow these in pure culture, if you want to study them you get a bucket full of mud from Woods Hole, and you drive that back to your lab.
13:21:39 And then if you want to extract bacteria from it. You stick a magnet next to the side of the side of the bucket of mud, you wait for about a half an hour.
13:21:48 We've got some ways of cleaning up that sample. And once you do that you get a density of like this. How far we're, we're sampling bacteria from within the month is entirely unclear to me.
13:21:59 When you do that because we have a protocol that says stick the magnet there for 20 minutes and then come back.
13:22:07 And that's sort of what we're left with. So, this is a natural sample. I don't know how representative the density is of nature. Yes, just be clear the speed of these bacteria is not controlled by the magnetic field strength.
13:22:22 No, so the speed of the cells is related to the, the number of Java, how well they're coordinate with one another, the average speed is about 75 micron per second.
13:22:32 And that varies by about a factor of two between common.
13:22:39 Is it 100 so one species or what's actually sir.
13:22:43 Is it a proton pump. Yeah.
13:22:46 Is it a proton pump. Okay, so because you need to take these bacteria, out of the mud. There have been about 30 papers ever published on them.
13:22:55 And so our ignorance is vast
13:22:59 from looking at the genome, everything seems more or less normal with the flagella so proton pump seems possible but, so can you do a Baroque style modulate the velocity I'm just curious.
13:23:10 Oh, if I change I haven't tried. That sounds like fun. Cool, thanks.
13:23:15 Is it like one species when you do your extraction protocol with magnet, you can attract they need a nice pieces which are in the model, which has is moving into Texas yeah so we typically get a small number of non multi-cellular might need a tactic bacteria.
13:23:33 We don't understand so we have some heuristics about how long to hold the magnet there, and the different steps and so after a full protocol the overwhelming majority of the Magneto tactic cells.
13:23:44 So, something about these timescales is preferentially selecting them, but the details of that are no, we did it enough, we found something that consistently worked, and then we sort of stopped thinking about.
13:23:59 Alright, so the next thing. So we've measured gamma. Now the next thing we want to do is figure out the rotational diffusion coefficient. So before I rotated the field.
13:24:09 You can look at the fluctuations in theta, averaging over many, many colonies blue dot show you the histogram of theta. And it fits reasonably well to a Gaussian but sample meaning variants.
13:24:25 And, and so knowing gamma that gives you the correlation time so you can get the rotational diffusion coefficient for measuring the the fluctuations. So we've got em, and we've got Dr.
13:24:35 Alright, so all of that should give you an idea of how this magnetic taxes works.
13:24:43 It's pretty simple, it's just you passively align with Earth's magnetic field, and you swim in the inner direction parallel to your magnetic moment.
13:24:52 The interesting part three and to be when we start thinking about what happens when we have collisions between these colonies and surfaces.
13:24:58 So let's start with an old model.
13:25:01 We know gamma, gamma gives us the correlation time for fluctuations in theta.
13:25:08 Knowing Dr. We know that the these magnetic fields that were studying are getting a standard deviation about 10 degrees. So you can imagine a colony swimming into a wall.
13:25:20 It's now fluctuating back and forth.
13:25:22 I can get a good estimate for what the distribution of those fluctuations are. So what's the rate at which you turn more than 90 degrees, so how often do you escape from the surface.
13:25:32 If you work that out in so far as that top right thing as a Gaussian, you get a rate of about once per three months.
13:25:39 Right, so naive we we should expect that when the cells, or I keep saying cells they're not sells their colonies.
13:25:47 When these colonies collide with a surface.
13:25:51 If a wall is doing nothing but preventing their, their forward motion, then they should just stick there and stay there for a very long time.
13:26:00 This is a wonderful thing about experiments.
13:26:03 So that red line shows a boundary, until we see the colonies swim towards the wall.
13:26:08 And if you track one you'll notice that, more or less, it hits the wall, rotates swims away from the wall and then moves back towards it.
13:26:18 Yeah.
13:26:20 Third,
13:26:26 know the Earth's magnetic field is about 60 miles for Tesla so we're at to Earth's magnetic field.
13:26:33 All of this randomness that we're seeing here is coming from them colliding with a wall.
13:26:44 That was the first experiment I showed that was just motion in the same microfluidic chamber with no wall. All I, all we did is it took the microscope moved the stage a little bit so we were focused on the wall.
13:26:56 And that's it.
13:26:58 If we increase the magnetic field.
13:27:01 We got more or less the same dynamics.
13:27:04 Except now all the colonies are confined much closer to the surface.
13:27:08 Maybe a little bit intuitive, but also not obvious, or certainly not obvious you know when compared with her null hypothesis.
13:27:19 So, in this bigger every red dot here shows and instantaneous position of one of these colonies, and that blue arches the trajectory of just one of these colonies that I selected because it looked because it was broadly representative and had enough motion
13:27:33 to what the you could really see it moving through the fluid.
13:27:36 So the basic image that I have of this is you have a colony which is moving deterministic way through the fluid. It's just turning to align with the magnetic field.
13:27:47 And when it hits the surface. There's something about that interaction that rotates it away from the surface, and also seems that they're sort of piling up within a distance of order, LL to remind you is the distance a colony swims before it aligns with,
13:28:02 with a applied magnetic field.
13:28:05 So you measure the density of colonies is the function of distance from the wall.
13:28:09 So that's the logarithm of the density.
13:28:12 We're getting more or less exponential profiles.
13:28:15 This is measuring distance in micron.
13:28:18 We know what L is for each one of these we measure the magnetic field at the beginning, and I know the applied magnetic field.
13:28:25 And so I know what else should be for each one of these.
13:28:28 So if I non dimensional SXYL, the data more of us collapses.
13:28:34 Alright, so let's, let's proceed to that to the idea was just tracing out a moment ago.
13:28:41 So, we can. I'm sorry, I'm ignorant, what's the Earth's magnetic field. 60 micro Tesla. Okay.
13:28:52 So sort of the lowest magnetic field I've got here is about one half is sorry twice earth's magnetic.
13:29:03 Alright so, in the simplest case of high magnetic field.
13:29:08 So in the limit that the rate at which you align with the magnetic field is fast compared to the rotational diffusion coefficient, you move, you are more or less moving deterministic Lee.
13:29:19 That's what this first equation is the second equation just as you move at a constant velocity of the direction of your magnetic moment.
13:29:26 Notice here I've got two equations with different with different units, and two unknown coefficient. So I cannot dimensionally is time by rate at which you align a non dimensional distance by the distance you swim.
13:29:37 And now this is a parameter free model. And so we can simulate. We've got a bunch of bacteria colliding with the wall, they move deterministic in the fluid.
13:29:47 And then, when once they hit the wall, they reorient to a random direction.
13:29:50 So, we can simulate that.
13:29:53 And so with no fit parameters we got a pretty good agreement between the non dimensional is distribution of colonies, and this zero parameter model.
13:30:04 All of this is to say that something funny is going on at the surface. Something funny is going on when these colonies are close to a wall. So, this is where we start thinking about very the magnetic field for sort of probe the near wall dynamics.
13:30:23 So, basically what we can do is we can increase the magnetic field, such that the typical distance microbes swim away from the wall is of order the colony diameter itself, we can turn up so we can turn up the field to the point where, even as they scatter
13:30:40 away from the wall, they're still trapped right next to it.
13:30:43 If you want a physical analogy for this.
13:30:46 These exponential profiles, that's what you would get for an ideal gas and a constant force field.
13:30:51 So now I need to do is I need to turn up what that force is until the penetration depth into the fluid is of order the colony diameter. So this act of gas, of particles banging around is need to condense on the surface of my of my wall as an act of two
13:31:08 dimensional fluid. Yes, she said in the simulation they reorient totally randomly went totally random Okay, okay. And I did that just didn't need to include another parameter.
13:31:22 Alex. Yes. What was the motivation for studying magnetic field strengths that are greater than the Earth's magnetic field.
13:31:28 Because what I'm trying to do is prob the.
13:31:43 So I've got these two different torques which I suppose are guiding these bacteria through the fluid, you've got Earth's magnetic field which is turning them towards the surface, and you've got the, and you've got scattering with the surfaces that will
13:31:47 hopefully get them around obstacles.
13:31:48 So,
13:31:51 the motivation to study Earth bank and to study magnetic fields different from Earth's magnetic field or that it's kind of like the probe more closely.
13:32:00 The, what, what I can do with the magnetic field by turning it up is keep them county stuck right by a wall and watch its dynamics, and I can study those dynamics to figure out what the wall was doing to the column.
13:32:18 Alright, so here's a 600 micro Tesco field. This is an orc so the geometry the experiment changed a little bit so now what we do is we take the glass slide and a cover slip separate them with a plastic spacer, fill that up with bacteria, and then we wrap
13:32:34 our microscope objective in magnetic wire and pass a current through it, and so we can generate a magnetic field between about half of a middle of Tesla and form of a Tesla.
13:32:43 And so now the magnetic field is aligned with the optical path of the experiment so all the back here we're going to swim up towards the cover slip and get sort of stuck on that cover on this cover slip and we're going to watch the move about the surface.
13:32:59 So here we are in her low magnetic field you can see some of them are in focused moving over the surface.
13:33:04 Here we are in her low magnetic field you can see some of them are in focus moving over the surface. And you can see the bright white dots, so there's white spots are anti shadows of light scattering through a colony, that is that is a few colony diameters away from the surface.
13:33:17 from the surface. We see them moving all hither and yon Yes, just for the drama Can you explain how you you know enrich these bacteria for your experiments. Sure. So, we drive down to Woods Hole, and we get a big painters bucket.
13:33:32 And then we go to a special pond there that that we've picked in collaboration with some friends at Montana who are studying for the underlying biochemistry.
13:33:40 So I've got a friend, Montana who's looking at genetic diversity within a single colony, doing some isotope tracing experience experiments and so we're collecting organisms from the same little pond, just so we can compare results.
13:33:52 So I've got this pond with, we've got some big. We've got some big paint buckets. We scoop up as much money as we can, we drive up to Massachusetts, and we take a.
13:34:03 We take a magnet we stick that to the side of the wall, and we wait about 20 minutes, and we go in with a pipe Pat and pathetic, and pipeline the fluid off of the surface of the, of the bucket.
13:34:15 And you see, and typically when you do that you see a little dark spot that some combination of a bunch of magnetic tactic cells, and then also a bunch of magnetic particles that are sort of distributed within the segment itself.
13:34:28 Sorry, I forgot an important thing before you put the magnetometer you shake the bucket and sort of lift all that sediment up and fluid is everything.
13:34:36 So once you pipe that off you stick that into a one milliliter centrifuge to a put a tiny magnet next to that and you wait another 30 minutes. Are you going with another pipe Pat, and you take 100 micrometres off of that and fill up the chamber, and we
13:34:50 we typically get thousands of cells, or thousands of colonies doing.
13:34:57 It's a lot of fun It feels quite gardening.
13:35:01 Sorry, can I miss the very beginning of your talk so please do so these ones have magnetic magnetic tactical behavior to adjust to this a sharp oxygen gradient right like the.
13:35:14 Yes, so the Redux gradients are changing over the course of a day, and these microbes need to move up and down vertically through the sediment, to avoid these ingredients so your experiments do you create such like oxygen.
13:35:26 So, when I saw the bucket that I have has every sort of every bacterium that the natural system has on it. So that's got ingredients that are no doubt fluctuating throughout the course of the day.
13:35:37 And so we can keep them alive in the bucket for a while, and pull cells out of that. What do we you know when you actually start imaging them. You do not do you have this, you know this, what so I do a constant chemical environment with a constant magnetic
13:35:50 field, or maybe I rotate the magnetic field, about oxygen concentration. So I just keep the oxygen concentration from whatever it wasn't the bucket. I don't change fluids or anything like that.
13:36:06 So here's what it looks like, have a higher magnetic field. So now you can see that there are fewer colonies swimming away from it. We've got this dense packing of these colonies that are moving to dimensionally over the surface of this banking into one
13:36:20 another jostling and pushing each other.
13:36:24 So what we're going to do is study these dynamics to learn what's going on with microbes, as they swim about the surface.
13:36:32 So the first thing that we're going to do is just characterize the, the motion of individual colonies.
13:36:38 The image processing on this is very difficult, you can see that every colony has a texture, and they don't all have the same brightness or darkness.
13:36:48 So the image processing of tracking these colonies is a little bit tricky.
13:36:52 So, the first thing we want to do which is measured the diffusion coefficient of these things moving over the surface.
13:37:00 Some that makes it easier to track them, and also sort of provides another piece of information is instead of thinking about the main square displacement of each individual colony.
13:37:11 I think that's a bad measurement because that's influenced by how long I can track the colony.
13:37:17 The time until it hits another colony. And all of these colonies are creating fluid flows. And so we want to keep track of how each individual colony is moving under its own Brownian motion versus how it's being affected by the flow is created by other
13:37:30 columns.
13:37:32 So what we're going to do is we're going to limit our attention to just two colonies that are that are going to collide at some time time t zero. I mean to measure the variance and distance between colonies in the one second before they collide with one
13:37:47 another.
13:37:49 So, if they're moving as Brownian particles. The variance should increase in proportion to the time, and the personality constant gives us the diffusion coefficient.
13:37:59 This looks like a pretty good line. And so we fit the slope of this to get the diffusion coefficient.
13:38:05 We repeat this that many magnetic fields. We, the magnetic, the diffusion coefficient decreases as we increase the magnetic field, the slope gets smaller and smaller.
13:38:16 And so at each magnetic field we can measure the diffusion coefficient in the colonies as they move laterally over the surface.
13:38:25 Alright, so we do that.
13:38:28 So here, as a plot, a log log part of the diffusion coefficient as a function the applied magnetic field.
13:38:35 The first thing to notice about this is that the diffusion coefficient that we measure the lowest magnetic fields are shockingly large.
13:38:43 This, this diffusion coefficient is about 100 micron squared per second.
13:38:49 For reference, something like eco VI is less than one micron squared per second. if you look at like swimming to the
13:39:02 temperature. Okay, so that's.
13:39:05 Sorry I was giving the rotation, so the, so it's so it's five times greater than.
13:39:11 Yeah, so, but but if you measure the diffusion coefficient of swimming can be demoed us that 6.8 mile squared per second, that's similar to teenagers which has a similar legislation, and size.
13:39:25 Sorry I was giving the diffusion coefficient for not for non tumbling equal.
13:39:31 The tumbling Of course increases the coefficient dramatically.
13:39:37 So, so one thing is that the diffusion coefficient is is quite large.
13:39:44 The other thing is that it decreases systematically with the applied magnetic field, you can understand this by thinking about gamma.
13:39:53 So, gamma is the rate at which you aligned with the magnetic field, it's important here for two reasons. The first one is that gamma gives the auto correlation time for velocity fluctuations.
13:40:00 So the higher gamma is the more quickly you align with the magnetic field. So the less time you have to move laterally for the surface.
13:40:07 It also gives the typical size of the fluctuations and feta.
13:40:12 So the.
13:40:14 So for a given rotational diffusion coefficient.
13:40:16 The larger the greater the magnetic field, the more narrowly confined you are and so the smaller your tangential velocities.
13:40:24 So putting these two effects together.
13:40:27 Effective 2d diffusion coefficient is the speed squared times the rotational diffusion coefficient divided by gamma square. So, gamma is proportional to be.
13:40:39 So if we set this profile to inverse magnetic field squared, we can get the rotational diffusion coefficient of the colonies were pressed up against the surface, the wall, or the surprising thing here is that the rotational diffusion coefficient seems
13:40:54 to increase by about a factor of eight. When the colonies are close to the wall.
13:41:01 Which.
13:41:02 Yeah, that's sort of in keeping with what we found earlier about as they slam into the wall, know they bang around the drama with her for Java, and that's going to move them about more quickly.
13:41:12 Yes.
13:41:19 You get it, you get it to be more reasonable
13:41:25 peculiarity, so a peculiar already shows up when you start thinking about the velocity fluctuations. So now we're trying to, you know, focus on a little bit more quick closely about what's going on when these colonies are closed, or close to the wall.
13:41:37 And if we look at all the colonies throughout the entire 2d fluid. We can look at the distribution of their velocity fluctuations, and lo and behold, it's Laplace distributed.
13:41:48 That wasn't obvious to me.
13:41:54 As you increase the magnetic field the distribution gets narrower. There are two effects which can cause this to be rounded out one of them is I'm confining it more narrowly to the magnetic field.
13:42:04 You'll also recall that as I increase the magnetic field I increase the concentration of colonies. And so they tend to bang into one another, more.
13:42:16 So it doesn't it surprised me that we were getting Laplace distributions for velocity fluctuations, and I don't have a great answer for that, but we can do an integral and try to get a clue.
13:42:30 So I think that the mistakes that I was making, so everything that you do everything I did here even if you keep the sign dependence.
13:42:37 The velocity fluctuation should always be normally distributed, maybe with, with a slight correction to the tail due to the, if you're not a approximating sign of theta, theta.
13:42:50 So,
13:42:54 one way to imagine how we could get a pass distributed distributions out of this is, if we imagine that this colony isn't just one individual cell that's swimming parallel to its magnetic moment.
13:43:07 It's a bunch of different cells, all stuck all moving together.
13:43:11 So if we imagine one individual cell that's pushing on the, on the colony close to a wall that individually could give us a normal distribution of velocity fluctuations.
13:43:22 That's his first term, and depending on where it is relative to all the other sellers on it if it's pushing it straight into the wall or off to the side.
13:43:31 If it has some different variants.
13:43:36 It could have some different variants so if we now integrate over all the cells in the colony.
13:43:41 There are so we need to scale, each, we need to do this some of normal distributions weighted by by the different variances that they could have.
13:44:00 Okay, cool. So, moving forward a little bit.
13:44:07 So so far all that was just thinking about the motion of the individual bacteria.
13:44:13 And I want to keep that the sort of focus of this talk is mostly what I'm interested in here is the ecology of these organisms as they as they move about.
13:44:23 So, if so, an interesting question to think about now is the large scale collective motion of the fluid as a whole so instead of tracking individual cells thinking about large scale structure of these 2d active fluids.
13:44:39 So see, increase the magnetic field we increase the concentration of these, we can measure the power distribution function, sort of the radio distribution function or the pairwise correlation function as we increase the magnetic field we increase the
13:44:53 concentration. The GFR shows a more structured thing we see these secondary and tertiary peaks, as this 2d fluid developed for locally try and give her locally training or triangular packing of colony.
13:45:09 So there's a percolation transition here.
13:45:17 So from each individual colony you can look at contacts with the surroundings, and you can find the size of different clusters.
13:45:20 If you look at the fraction of counties belong to a spanning cluster that you see a percolation transition there with a, with large fluctuations near a critical magnetic field.
13:45:32 I'm sorry Alex I missed How did you define if there's a link.
13:45:36 If they're touching, I see. Yeah.
13:45:42 Because this is a rigidity jamming transition as well. Yeah.
13:45:47 I'll show that better in a moment. So a difference that's difference between these and how we normally think about percolation transitions is that these are actively moving about.
13:45:58 So if we look at these videos this one slow down by a factor of four, we have these 2d fluids reorganizing in space with these large voids forming and pushing through the pushing through the fluid.
13:46:11 And one thing that we can do now is look at the way that the density fluctuations relax. So a good way of characterizing all of this
13:46:22 is to define the intermediate scattering function. So this is a measure the density of colonies at a specific point look at its. Take the look at the power spectrum of that we're looking at correlations between density fluctuations without waypoints que
13:46:46 Sorry.
13:46:47 So, basically this is just how quickly, density fluctuations relax as a function of how large of a scale we're looking at.
13:46:55 So if we started off on a short scale something of order the size of the colony, the correlations fall off quickly in about 10 seconds, everything is reorganize.
13:47:06 We've all cat density fluctuations on the Scott size of this on the scale of the system. After about a second, they there, they reach a plateau and then they just have to stick there.
13:47:16 And so we're close to a German transition now. And so the the dynamics of this arrested by that Trump.
13:47:23 If we work on intermediate line sales order the size of the void.
13:47:27 You can see a logarithmic a logarithmic decay of the, of the density fluctuations. Yes,
13:47:41 magnetic field is pointing out of the board, and you're looking straight down at.
13:47:49 Nope, no force is squeezing.
13:47:52 This is just volume exclusion.
13:47:59 Sorry, extra weight.
13:48:05 So, so at some point I run out of colonies and the main fluid.
13:48:11 And so beyond search magnetic field at this other concentration that we load it with you don't get more. So the important thing to do in parallel to that percolation transition is in addition to showing how the how everything varies with magnetic field
13:48:29 also very the concentration of the bulk fluid, because that's the important second parameter.
13:48:35 Right now, everybody is on the surface.
13:48:38 I'm sorry. The question was, the questions were what direction were the magnetic fields pointing and what's preventing these boys from getting filled in, just happened to be operate in the density in the bulk which gave you percolation at the surface,
13:48:51 right. So, if I'm at a high enough density in the bulk.
13:48:57 So, anything above that, at some magnetic field I need to hit a jamming transition. Oh, so that specific value of two mega Tesla's that's specific to the concentrations that are arbitrary really started with.
13:49:10 But as long as I'm above some threat is to obviously on, if I have one county in my entire chamber. I've never even got a percolation transition there, because I've only got one colony.
13:49:20 But if I've got enough at some point I'll hit a transition.
13:49:25 So maybe it's maybe it's only I was last year but just let me ask one more question here.
13:49:32 So, you see, what is on this 2d plane, and there is an entire half.
13:49:38 You know half a 3d universe, which you don't see. Yeah, and what you are saying is that in this universe, everything is jam so the particles cannot reach those voids on the surface because something out of the plane is being jammed.
13:49:51 Is it, is it was LFI
13:49:56 back to the video.
13:49:59 The high field. So I've got a bunch of colonies are more or less at the surface. You can see new county is trying to find places to land, and some of them will try to land on cells that are already pressed up against the wall and then they'll sort of
13:50:15 about until they find it an empty space. If I were to, let's say, so right now the area fractions hacking the surface is sort of, you know, 60%.
13:50:24 So if I put twice as many colonies in my original chamber and have them all come to the surface, presumably I'd get a much tighter packing, there would be more colonies forming the second layer of colonies behind.
13:50:47 So getting back to a commentary.
13:50:52 What we started all of this by thinking about the about the ways that microbes can navigate through a complex pore space.
13:51:00 And so if we just consider a microbe that swimming through such a complex might pore space that that's taking a direction to swim by aligning with some external field.
13:51:11 So in this case it's a magnetic field, but this is a common problem and you can also imagine bacteria aligning with a gravitational field or a white gradient, or chemical gradient.
13:51:20 So there's some external field that these microbes are aligning with.
13:51:25 If they align completely without, without external field and just swim in that direction, inevitably, inevitably, they hit some surface. And so in, in addition to moving into fixed direction they also scatter, and maybe the scattering is coming from the
13:51:38 collisions as we saw here. Or maybe it's coming from run and tumble or rotational diffusion,
13:51:45 or any other, so the sort of claim that I want to make is that evolutionarily this strategy only makes sense. If the ratio of these rates is something of order one.
13:51:56 The idea being that is your scattering rate is tremendously high than all I'm doing is moving randomly through the poor space.
13:52:06 So if I'm moving in terms of at random and not cut and so in the limit that this thing goes to zero.
13:52:14 I'm not hiding to the field I'm just moving randomly about, and if I move randomly about, you know, half the time I'm going to swim against the gradient end up in the overlying water, and at best I can only escape from the surface, yeah at a rate that
13:52:29 increases practice square root of time so as these as these option gradients. Push down from the surface at some point they're going to catch me if all I'm doing is moving around.
13:52:39 So if this number is zero, I burn to death, either by swimming into the Evergreen water, or by just not running fast enough.
13:52:49 Yes,
13:52:52 the scattering rate presumably depends on the properties of the, of the sand of the market that is bacteria Yeah, right. So in principle if.
13:53:02 Does this mean that that these, these kinds of bacteria are limited to being in very certain kinds of materials because otherwise you know the alignment rate for match their scattering rates.
13:53:16 So, I'll get to that in a moment.
13:53:18 So, So I'm convinced that to you can't be zero. It also can't be infinity. So if it's infinity, you don't scatter at all You only swim in a fixed direction, which means that in that inevitably you're going to quickly hit some obstruction, and we're going
13:53:34 to get stuck there until the auction gradients come and burn.
13:53:37 So this number can be infinity, it can't be zero.
13:53:41 So it needs to be, you know, something not so far from what what makes it nice to work with these Magneto tactics cells, is that we can get the alignment rate and measure well from the, from from Earth's magnetic by Verizon magnetic field and measuring
13:53:57 gamma well, and similar way by tracking how these microbes move through the environment, how they bounce off of things. We get the rate at which they scattered scattered from surfaces, as the speed they swim, compared to the typical size of the poor space.
13:54:14 So, taking a good estimate for the size of the Force base we know that gamma is an Earth's magnetic field, we know what you is, and we can get a good estimate of the pore space, and this number ends up being about a third.
13:54:30 So it's sort of in keeping with our intuition that this number has to be, you know, not so not so many orders of magnitude away from one
13:54:40 sort of a more interesting way of of setting this up, is I can write gamma in terms of the magnetic moment and Earth's magnetic field. So I can just reorganize that equation a little bit on the left here, I've got all the coefficients that presumably
13:54:57 natural selection could act on things like the magnetic moment.
13:55:02 Em, the speed that the county moves, and the colony radius.
13:55:07 And on the right, I've got environmental constraints, the viscosity of the water, how, how porous the space I'm moving through his and Earth's magnetic field.
13:55:17 What I sort of like about the this this similarity is that this is now know a reflection of the general sense that we have that, that phenotype should be somehow shape to match their environment.
13:55:31 This is a way of writing that, that actually has corrected units and where we can measure things.
13:55:39 So, when we were talking the other day made a very nice suggestion of putting these buckets of mud and Helmholtz coils and varying what magnetic fields are growing in, and seeing if we can't evolve them to change their magnetic moments or swimming speeds.
13:55:58 I think that's a lovely idea.
13:56:04 So be here. So, sorry, the question is what is be is be the total magnitude of the magnetic field or is be as the vertical component of the magnetic field.
13:56:17 Be Here is the total magnitude of the magnetic field, because that's what determines how quickly you align with the external field, it doesn't point you in exactly the right direction.
13:56:27 But it does tell you how quickly your how quickly you align with the ambient have a problem is immediately jumping into evolutionary experiments here, because the whole thing is very heterogeneous right you you just explained us earlier on that your magnetic
13:56:46 model of magnetic moment varies by factor to, if you will believe the cube of the radio soul so there is quite a bit so all of the parameters are already.
13:56:58 The house, we have a heterogeneous population, and really evolved that much bigger well, or is a place already.
13:57:10 So perhaps a better so I wrote it this way.
13:57:13 But because it's sort of clarity associated with their rights, the better way of writing that is derived gamma over you.
13:57:21 That's the distance they swim before they aligned with the magnetic field.
13:57:25 And so that is something that combines the magnetic moment the radius and the and the speed. All these very l just if you do all the fits. The. L as a total varies less than the independent measurements that you get of ml and you.
13:57:46 So it does seem that they're correlated with one another.
13:57:49 I'm still trying to pick apart there's correlations, because you know it's noisy data and I've got like 100 sales here. So a lot of what we're doing is trying to get better measurements for that.
13:58:00 If you trade just to make them more homogeneous by for instance, apply in a magnetic field periodically or something and then select and only the particles which feed a particular profile, you know, you know what I mean that like you like the way you
13:58:17 select for instance for DNA of a particular length, but it's reporters medium, and you can do the same analog of yeah what we've, we've tried the.
13:58:27 There are a million parameters that you need to fix. To do that, because the porosity materials that you're swimming through how long it is.
13:58:35 So, there's a bunch of parameters that you need to adjust to separate them out. And so far we haven't been able to do that without crashing at our yields to a point where it's really hard to study anything.
13:58:46 So it's something that we've worked on but it's not trivial. Good.
13:58:51 I have a similar question but for different motivation instead of trying to make them uniform to somehow study the effect better, can you capitalize on this natural variation is like standing variation to check us kind of selection is favoring the combinations
13:59:08 that you'd expect, like if you modify your protocol of how long you're strong, like, how long you keep the magnet or something does it enrich in different sizes or whatever how we how you predict.
13:59:21 I mean, oh that's.
13:59:22 That seems hard but I don't know, something.
13:59:30 I agree that they're similar information and trying it that way. I kind of like the sort of gross simplicity of actively trying to get them to evolve in their natural habitat, or, you know, the natural habitat that we have them living in in the in the
13:59:46 MCG which is course, and diverse it, you know, we've got every sort of bacteria that you can imagine living in there, you know, Can we do this and something that's approaching nature.
14:00:01 But yes, maybe you're lazy.
14:00:11 Okay, so the point was that by increasing the magnetic field I might just select for the distribution for the part of the distribution of cells, or the part of the distribution of colonies that are more close to, you know, the five magnetic field that
14:00:27 I'm imagining.
14:00:29 I'm satisfied with that. I think that there are a bunch of neat questions you can ask about how evolution would happen on these, in particular, each one of these colonies is composed to 60 different bacteria.
14:00:41 It's not clear if they can change their magnetic moment by, you know right through regulation, or if they've got you know some gene that says grow a magnetic moment this length, grow a magnetic crystal to this length, in which case you would have to evolve
14:00:56 that, but the selection is happening on the scale of a colony not on the scale of the individual so so there's a lot of peculiarities there, and it would be neat to poke at there's direct, you're ready to this action in your isolation protocol right you
14:01:12 You're ready this action in your isolation protocol right you put a magnet so you presumably pick the fastest one so we're swimming towards your magnet.
14:01:22 Yeah, there's some
14:01:25 cool. If you're a grad student or a postdoc, this is a great class.
14:01:29 That person off on the right there is 100 recently called her own. She is an extraordinarily talented undergraduate, who did basically all the experiments that I presented today.
14:01:39 They're very difficult experiments to do and she did an outstanding job. She's at Brown University now, and last I heard she still looking for an advisor.
14:01:48 So if you know somebody a brown who needs a really talented graduate students.
14:01:55 Also I want to postdoc and grad students. So, you know, talk to me if you're into that sort of thing.
14:02:12 One like general question Do you have any thoughts as to why Magneto taxes in particular if they're looking to go up a chemical gradient why not simply find some way to directly sense the chemical gradient.
14:02:25 Why Why am I so there are a few points to that the first one is, why does make why magnetic taxes. I think the simplest and most honest answer is, it is a way and evolution is good at finding every possible way.
14:02:39 And so it's going to show up in something.
14:02:42 Now you could ask why is it going to be better than coupling to other fields such as chemical gradients. So these things based off of their genome here to metabolize sulfate, there's an enormous quantity of sulfate in seawater.
14:02:56 And so the sort of gradients you get from that are prison, it's you're trying to measure a small change over a large background. So maybe measuring chemical grains directly isn't good enough.
14:03:08 There's a whole point of Why do you look at magnetic fields as opposed to gravitational fields. The typical answer there is a gravitational torque is going to be sort of your density contrast times the radius of your cell and the things that people say
14:03:23 is that, you know, as the cell gets smaller. The gravitational torque also gets smaller and at some point it's going to get, you know confused by rotational Brownian motion.
14:03:36 That can be a benefit.
14:03:38 The other point is that works well if you're thinking about an individual cell, I'm now thinking about 60 cells all stuck together. And this organism is now as big as some as some microbes that do gravity taxes.
14:03:52 So why don't do they do that you know evolution might be dumb, I don't know, I don't want to judge.
14:03:59 Thank you.
14:04:00 Come back to the swimming question, how they pick a direction. Yeah, so I mean there's some a similar three different starts in swimming randomly but then is getting rotated around by the magnetic field.
14:04:13 That might change them the direction, which is them trying to swim listeria you can have a completely spherical ball is like the stereo. Yeah, and it'll, it'll go off shooting things often differently for a while and then we'll go from one direction.
14:04:28 There's a symmetry breaking things that will tend to, you know, a couple of back to the economics which will tend to make going some directions and if you had something like that which then starts off in a sort of random direction, then might rotate the
14:04:42 correlations in where which way the flagella are going to enjoy isn't like that yeah so through the volume of the collective interactions between, I mean I would say so I'm desperate to study it, it's very difficult to study because you can't do you know
14:04:58 anything like knockouts. I think the first obvious thing to do is to just see how many cells are taking part in this large scale motion so we're going to put tracer particles all around these and measure the velocity field of the fluid around these swimming
14:05:21 colonies that will give us an idea of how well correlated their the flagella are over the surface. I think that's a useful measurement. If we do that really really really well, maybe you know there's going to be greater fluctuations of the equator.
14:05:28 For example, so the question of how do all these colonies know how do all these colonies exert a force in the same direction.
14:05:37 And why that direction is parallel to the magnetic moment.
14:05:40 Now it seems to be quite robust, a lot of the experiments that we're doing right now is just trying to confuse them. So we're putting them in, so you can interfere with magnetic taxes by shining blue light on them, you can imagine that a good external
14:05:54 signal if your sweat if you think you're swimming north and you're actually swimming south, you're going to get close to the surface. And now the sun is shining down on you.
14:06:02 And that means that you've made a mistake.
14:06:04 So, by shining blue light on them you can change South speakers to North seekers. So we're trying to systematically confuse them by training blue lights on them, and then keeping them in zero magnetic field, and just letting them encounter perturbations
14:06:26 and we'd love to be able to just see these things learn how to become magnetic. You don't know whether the jello or old organization direct help them and tracking the flow of particles around them should give good intuition for that something amazing
14:06:36 about them is
14:06:47 this thing and panel, he here is still magnetic tactic.
14:06:52 Right. If you can, grossly change the distribution of cells over the surface and their ability to swim in a common direction remains intact
14:07:05 in vivo Soames routed around within the cells they're pretty fixed.
14:07:11 It seems that they're pretty fixed, you can imagine that as you're splitting like this. Now your magnetic moment relative to the outside can can change from pointed outwards to pointed parallel to pointed inwards.
14:07:23 And then in words again as you split.
14:07:26 So tracking them in three dimensions, I think is interesting.
14:07:31 There are lots of curious. So if you look down on them so if you look down on the axis parallel to the magnetic moment. You can see that there is a very regular distribution of cells.
14:07:43 You can see that they're packed along these spirals.
14:07:48 We've got one can focus on image from which we can reconstruct the 3d distribution of colonies.
14:07:54 And it's not inconsistent with a Fibonacci of hacking that you would get for seeds in a strawberry back can be relevant to how you pack the magnetic zones and how you can.
14:08:06 How you can coordinate growth as a whole.
14:08:10 So, one big projects that we're getting ready to do is just make a library of 1000 packages of cells at different stages in their development, try to tease apart, how they're aligning their magnetic moments and how they're coordinating
14:08:25 this thinking about the phylogenetic and spatial distribution fairly large scales. So you started, you mentioned that these McDonald tactic bacteria are primarily in the Delta protein bacteria, and that they're sulfate reducing, we think, mostly Ok, so
14:08:57 Yet oxygen is important probably universally is a powerful electron acceptor for generating ATP.
14:09:01 So I'm just curious.
14:09:04 Yeah, so So are there other non Delta Proteus bacteria that are that are my Ada tactic Yes, and then also are there, non Delta produce bacteria that live in sulfur rich environments that have the ability to use Magneto taxes, that's a totally reasonable
14:09:23 question, I can't remember the answers to either others, there are a bunch of different a bunch of different back into tactic bacteria and I'm inadequate taxonomists to remember if they're all in the dojo do bacteria is it's such a complex trade it seems
14:09:39 it seems to be really, you know, it was an amazing presentation of sophistication and I'm kind of wondering if this just kind of happened once. No, it's pretty clear.
14:09:48 So there are some good articles that make I think compelling arguments and I needed a tax this evolve separate, but to the best of your understanding within the Delta produce bacteria.
14:09:59 I'm not going to answer that because there's, there's a 50%, I can either say yes or no and there's at least 50% you can say wrong. Okay.
14:10:08 Thanks. Appreciate it. Yeah.
14:10:10 Do you see gradients north to south, if you're in some mud flat and you sample your you know your magnetic toxic bacteria on the north side of the mud, whatever homogeneous piece of mud in on this house, so we don't sample how widely in the salt marsh,
14:10:31 because we like to have some idea of where we are.
14:10:35 And just, we don't want to do things that randomly we've got some places, we'd like we want to do that. We have tried to enrich bacteria from the north side of the bucket, versus the south side of the bucket.
14:10:46 And there's not a substantial change.
14:10:51 We said small compared to the variability between different interactions.