Arash Komeili cell biologist, Assc. Prof. plant and microbial biology UC Berkeley. His research uses bacterial magnetosomes as a model system to study the molecular mechanisms governing the biogenesis and maintenance of bacterial organelles. Part1

Transcript

Speaker 1: Spectrum's next.

Speaker 2: Okay.

Speaker 3: [inaudible] [inaudible].

Speaker 1: [00:00:30] Welcome to spectrum the science and technology show on k a l x Berkeley, a biweekly 30 minute program bringing you interviews, featuring bay area scientists and technologists as well as a calendar of local events and news.

Speaker 4: Hi, and good afternoon. My name is Brad Swift. I'm the host of today's show. We are doing another two part interview on spectrum. Our guest is Arash Kamali, [00:01:00] a cell biologist and associate professor of plant and microbial biology at cal Berkeley. His research uses bacterial magneta zones as a model system to study the molecular mechanisms governing the biogenesis and maintenance of bacterial organelles. Today. In part one, Arash walks us through what he is researching and how he was drawn to it in part two, which will air in two weeks. [00:01:30] He explains how these discoveries might be applied and he discusses the scientific outreach he does. Here's part one, a rush. Camelli. Welcome to spectrum. Thank you. I wanted to lay the groundwork a little bit. You're studying bacteria and why did you choose bacteria and not some other micro organism to study? One

Speaker 5: practical motivation was that they're easier to study. They're easier to grow in [00:02:00] the lab. You can have large numbers of them. If you're interested in a specific process, you have the opportunity to go deep and try to really understand maybe all the different components that are involved in that process, but it wasn't necessarily a deliberate choice is just as I worked with them it became more and more fascinating and then I wanted to pursue it further.

Speaker 4: And then the focus of your research on the bacteria, can you explain that?

Speaker 5: Yeah, so we work with [00:02:30] a specific type of bacteria. They're called magnate as hectic bacteria and these are organisms that are quite widespread. You can find them in most aquatic environments by almost any sort of classification. You can really group them together if you take their shape or if you look at even the genes they have, the general genes they have, you can really group them into one specific group as opposed to many other bacteria that you can do that. But Unites Together as a group [00:03:00] is that they're, they're able to orient in magnetic fields and some along magnetic fields. This behavior was discovered quite by accident a couple of times independently. Somebody was looking under a microscope and they noticed that there were bacteria were swimming all in the same direction and they couldn't figure out why. They thought maybe the light from the window was attracting them or some other type of stimuli and they tried everything and they couldn't really figure out why the bacteria were swimming in one direction except they noticed that [00:03:30] regardless of where they were in the lab, they were always swimming in the same geographic direction and so they thought, well, the only thing we can think of that would attract them to the same position is the magnetic field, and they were able to show that sure enough, if you bring a magnet next to the microscope, you can change the swimming direction.

Speaker 5: This type of behavior is mediated by a very special structure that the bacteria build inside of their cell, and this was sort of [00:04:00] what attracted me to it. Can you differentiate them? The UK erotic? Yeah. Then the bacterial, can you differentiate those two for us so that we kind of get a sense of is there, they're easy, different differentiate, you know the generally speaking you out excels, enclose their genetic material in an organelle called the nucleus. They're generally much bigger. They have a lot more genetic information associated with them and they have a ton of different kinds of organelles that perform [00:04:30] functions. All these Organelles to fall the proteins to break them down. They have organelles for generating energy, but all those little specific features, you know, you can find some bacterium that has organelles or you can find some bacterial solid that's really huge. Or you can find some bacteria so that encloses its DNA and an organelle.

Speaker 5: It's just that you had accels have all of them together. Many of the living organisms that you encounter everyday because you can see them [00:05:00] very easily. Are you carry out, almost all of them are plants and fungi and animals. They're all made up of you. Charismatic cells. It's just that there's this whole unseen world of bacteria and what function does that capability serve, that magnetic functions that it can be realized that yet in many places on earth, the magnetic field will act as a guide through these changes in oxygen levels, sort of like a straight line through these. These [00:05:30] bacteria are stuck in these sort of magnetic field highways. It's thought to be a simpler method for finding the appropriate oxygen levels and simpler in this case means that they have to swim less as swimming takes energy. So the advantage is that they use less energy, get to the same place, that bacteria and that doesn't have the same capabilities relatively speaking, as a simple explanation, it's actually, because it is so simple, the model, you can kind of replicate [00:06:00] it in the lab a little bit.

Speaker 5: If you set up a little tube that has the oxygen grading and then the bacteria will go to a certain place and you can actually see that they're sort of a band of bacteria at what they consider for them to be appropriate oxygen levels. And then if you inject some oxygen at the other end of the tube, the bacteria will swim away from this oxygen gradient. Now, if you give them a magnetic field that they can swim along, they can move away from this advancing oxygen threat much more quickly than [00:06:30] bacteria that can't navigate along magnetic fields. So that's sort of a proof of concept a little bit in the lab. There's a lot of reasons why it also doesn't make sense. For example, some of these bacteria make so many of these magnetic structures that we haven't talked about yet, but they make so many of these particles way more than they would ever need to orient in the magnetic field.

Speaker 5: So it seems excessive. There are other bacteria that live in places on earth where there is not really this kind of a magnetic field guide. And in those environments there's [00:07:00] plenty of other bacteria that don't have these magneto tactic capabilities and they still can find that specific oxygen zone very easily. So in some ways I think it is an open question but there isn't really enough yet to refute the kind of the generally accepted model on the movement part of it. You were mentioning that they use magnetic field to move backwards and forwards. Only explain the limiting factor. Yeah, that's [00:07:30] an important point actually because it's not that they use the magnetic field for sensing in a way. It's not that they are getting pulled or pushed by the magnetic field. They are sort of passively aligned and the magnetic field sort of like if you have two bar magnets and if one of them is perpendicular to the other one and you bring the other one closer, I'll just move until they're parallel to each other.

Speaker 5: This is the same thing. The bacteria have essentially a bar magnet and inside of the cell and so the alignment to the magnetic field [00:08:00] is passive that you can kill the bacteria and they'll still align with the magnetic field. The swimming takes advantage of structures and and machines that are found in all bacteria essentially. So they have flagella that they can use to swim back and forth as you mentioned. And they have a whole bunch of other different kinds of systems for sensing the amount of oxygen or other materials that they're interested in to figure out, should I keep swimming or should I stop swimming? And [00:08:30] as I mentioned earlier, the bacteria are quite diverse. So when you look at different magnatech active bacteria, the types of flagella they have are also different from each other. So it's not one universal mechanism for the swimming, it's just the idea that that the swimming is limited by these magnetic field lines.

Speaker 6: [inaudible] [inaudible].

Speaker 5: Our guest today on spectrum is [inaudible] Chameleon, a cell biologist

Speaker 7: and associate professor at cal Berkeley. In our next segment, [00:09:00] Arash talks about what attracted him to study the magnetism and why it remains in some bacteria and not others. This is k a l x Berkeley. So

Speaker 5: let's talk about the magnetic zone, right? This is sort of my fascination. I was a graduate student at UCF and I studied cell biology. I use the yeast, which are not bacteria but in many ways they are kind of like bacteria. They're much simpler to study than maybe other do care attic [00:09:30] organisms and we have genetics available and so I was very fascinated by east, but I was studying a problem with XL organization and communication within the cell and yeast. We were taught sort of as students in cell biology at the time, that cell organization and having compartments in the cell organelles basically that do different functions was very unique feature of you carry attic cells and there's one of the things I've defined them. I received my phd to do a postdoctoral fellowship. I happen to be [00:10:00] in interviewing at cal tech and professor Mel Simon there he was talking about all kinds of bacteria that he was interested in and he said there's these bacteria that have organelles and I just, it kind of blew my mind because we were told explicitly that that's not true and in many textbooks, even today it still says that bacteria don't have organelles.

Speaker 5: I learned more about men and I learned that these magnatech to bacteria that we've been talking about so far, you can actually build a structure inside of the cell, out of their cell membrane and within [00:10:30] this membrane compartment, it's essentially a little factory for making magnetic particles so they can build crystals of mineral called magnetite, which is just an iron oxide. Every three or four and some organisms make a different kind of magnetic minerals called Greg [inaudible], which is an iron sulfur mineral, but these are perfect little crystals, about 50 nanometers in diameter, and they make a chain of these magnesiums, so these membrane enclosed magnetic particles. [00:11:00] This chain is sort of on one side of the cell and it allows the bacteria to orient and magnetic fields because each of those crystals has this magnetic dipole moment in the same direction and all those little dipole moments interact with each other to make a little bar magnet, a little compass needle essentially that forces the bacterium to Orient in the magnetic field.

Speaker 5: When I heard about this, I realized that this is just incredibly fascinating. Nobody really knew how it was that the membrane compartment forum [00:11:30] or even if it formed first and the mineral formed inside of it. There wasn't much or anything known about the proteins that were involved in building the compartment and then making the magnetic particle. It just seemed like something that needed to be studied and it was fascinating to me and I've been working on it for 1213 years now. Have we covered what the of the magnetic is that idea behind the function of the magnetism, which is the [00:12:00] structures of the cells build to allow them to align with a magnetic field. We think that function is to simplify the search for low oxygen environments. That's the main model in our field and I think there are definitely some groups that are actively working on understanding that aspect of the behavior better.

Speaker 5: How it is that the bacteria can find a certain oxygen concentration. These bacteria in particular, what are the mechanics of them swimming along [00:12:30] the magnetic field and the, is there some other explanation for why they do this? For example, if they are changing orientations into magnetic field, can they sense the strain that the magnetic field is putting onto the cell? Can that be sensed somehow and then used for some work down the line and there are groups that are actively pursuing those kinds of ideas. You were mentioning that this is a particular kind of bacteria that has this capability, right, and others don't. Right. Yet both seem to be equally [00:13:00] effective and populating the water areas that you're studying. No apparent advantage. Disadvantage, so winning in Canada? Yeah, I mean it's a lot of the Darwinian, you could say as long as it's not severely disadvantageous, then maybe they wouldn't be a push for it to be lost.

Speaker 5: What is kind of intriguing a little bit is there's examples of magna detective bacteria in many different groups, phylogenetic groups, so many different types of species that will be, let's [00:13:30] say bacterium that normally just lives free in the ocean and then I'll have a relative that's very similar to it, but it's also a magnet, a tactic. In recent years, people have studied this a little bit more and we know now what are the specific set of genes that allow bacteria to become magnetic tactic. So you can look at those genes specifically and say, how is it that bacteria that are otherwise so different from each other can all perform the same function? And if you know the genes that build the structures that allow them to orient [00:14:00] the magnetic fields, you can look at how different those genes are from each other or has similar they are.

Speaker 5: And normally with a lot of these types of behaviors in bacteria, there's something called horizontal gene transfer that explains how it is that otherwise similar bacteria can have different functionalities. For example, you can think of that as bacteria being cars and everybody has sort of the same standard set of know features on the car. But you can add on different features if you want to. So you can upgrade and have other kinds of features like leather [00:14:30] seats or regular seats. And so the two cars that have different kinds of seats are very similar to each other. It's just one that got the leather seats. And so these partly are thought to occur by bacteria exchanging genes with each other. Somebody who wasn't magna tactic maybe got these jeans from another organism, but when people look at the genes that make these mag Nita zones, these magnetic structures inside of the cell, what you see is that they appear to be very, very ancient.

Speaker 5: So it doesn't seem like there was a lot of recent [00:15:00] exchange of genes between these various groups of bacteria to make them magna tactic. And it almost seems to map to the ancestral divergence of all of these bacteria from each other. One big idea is that the last common ancestor of all these organisms was mag new tactic and that many, many other bacteria have sort of lost this capability over what would be almost 2 billion years of evolution for these bacteria. And then some have retained it. [00:15:30] Those of that have retained it is it's still serving an advantage for them, or is it just sort of Vista GL and they have it and they're sort of stuck in magnetic fields and they have to deal with it? No, but nobody really knows. Actually. The other option is that there was a period of horizontal gene transfer, but it was a very long time ago so that the signature is sort of lost from, again, a couple of billion years of evolution or divergence from each other, but it really looks like whenever this process happened, it was quite anxious.

Speaker 3: [00:16:00] You are listening to spectrum on KALX Berkeley. Our guest is Arash [inaudible]. In the next segment, rush talks about organelles in bacterial cells.

Speaker 5: [00:16:30] Explain what the Organelle is, so there's a lot of functions within the cell that need to be enclosed in a compartment for various reasons. You can have a biochemical reaction that's not very efficient, but if you put it in within a compartment and concentrates, all of the components that carry that reaction, it can be carried out more efficiently. The other thing is that for some reactions to to happen, you need a chemical environment that's different than the rest of the cellular environment. You can't convert [00:17:00] the whole environment of the cell to that one condition. So by compartmentalizing it you able to carry it out and often the products of these reactions can be toxic to the rest of the cell. And so by componentizing again you can keep the toxic conditions away from the rest of the, so these are the different reasons why you care how to excels.

Speaker 5: Like the cells in our body have organelles that do different things like how proteins fold or modify proteins break him down and in bacterial cells it [00:17:30] was thought that they're so simple and so small that they don't really have a need for compartments. Although for many years people have had examples of bacteria that do form compartments. You carrot axles are big and Organelles are really easy to see where the light microscope so you can easily see that the cell has compartments within it. Whereas a lot of bacteria are well studied, are quite simple, they don't have much visible structure within them. And that's maybe even further the bias that there is some divide and this [00:18:00] allowed you carry out access to become more complex, quote unquote, and then it just doesn't exist in bacteria. How is it that they then were revealed? I think they'd been revealed for a long time.

Speaker 5: You know, for example, there's electron microscope images from 40 years ago or more where you see for example, photosynthetic bacteria, these are bacteria that can do photosynthesis. They have extensive membrane structures inside of the cell that how's the proteins that harvest light and carry [00:18:30] out photosynthesis and they're, it seems like the idea for having an Organelle is that you just increased it area that you can use for photosynthesis sorta like you just have more solar panels if you just keep spreading the solar panels. Right. So that in this way, by just sort of making wraps of membranes inside of the cell, you just increased the amount of space that you can harvest light. So those were known for a long time and I think it just wasn't a problem that was studied from the perspective of cell biology and cell [00:19:00] organization that much. That's sort of a different angle that people are bringing to it now with many different bacterial organelles.

Speaker 5: And part of the reason why it's important to think of it that way is that of course what the products of the bike chemistry inside of the Organelles is fascinating and really important to understand. But to build the organ out itself is also a difficult thing. So for example, you have to bend and remodel the cell membrane [00:19:30] to create, whether it's a sphere or it's wraps of membrane, and that is not a energetically favorable thing to do. It's not easy. So in your cataract cells, we know that there are specific proteins and protein machines. Then their only job is really to bend and remodeled the membrane cause it's not going to happen by itself very easily. And with all of these different structures that are now better recognized in bacteria, we really have no idea how it is that they performed the same function. Is [00:20:00] it using the same types of proteins as what we know in your care at excels or are they using different kinds of proteins?

Speaker 5: That was sort of a very basic question to ask. How similar or different is it than how you carry? Like some makes an Oregon own fester was one of the first inspirations for us to study this process in magnatech the bacteria. And what sort of tools are you using to parse this information? In our field we use various tools and it's turned out to be incredibly beneficial [00:20:30] because different approaches have sort of converged on the same answer. So my basic focus was to use genetics as a tool. And the idea here was if we go in and randomly mutate or delete genes in these bacteria and then see which of these random mutations results in a loss of the magnetic phenotype and prevents the cell from making the magnetism Organelles, then maybe we know [00:21:00] those genes that are potentially involved. And so that was sort of what I perfected during my postdoctoral fellowship.

Speaker 5: And that was my main approach to study the problem. And then on top of that, the other approach has been really helpful for us. And this is again something we've worked on is once we know some of the candidate proteins to be able to study them, their localization in the cell and they're dynamics, we modify the protein. So that they're linked to fluorescent proteins. So then we can, uh, use for us in this microscopy to follow them within the cell. [00:21:30] Other people, their approach was to say, well, these structures are magnetic. If we break open the cell, we can use a magnet and try to separate the magnesiums from the rest of the cell material. And then if we have the purified magnesiums, we can look to see what kinds of proteins are associated with them and sort of guilt by association. If there is a protein there, it should do something or maybe it does something.

Speaker 5: That was the other approach. And the final approach that's been really helpful, [00:22:00] particularly because Magno take it back to your, our diverse, as we talked about earlier, is to take representatives that are really distantly related to each other and sequence their genomes. So get the sequence of their DNA and see what are the things that they have in common with each other. Take two organisms that live in quite different environments and their lineages are quite different from each other, but they both can do this magnetic tactic behavior. And by doing that, people again found [00:22:30] some genes and so if you take the genes that we found by genetics, random mutations of the cell by isolating the magnesiums and cy counting their proteins, and then by doing the genome sequencing, it all converges on the same set of genes.

Speaker 2: [inaudible] this concludes part one of our [00:23:00] interview. We'll be sure to catch part two Friday July 12th at noon. Spectrum shows are archived on iTunes university.

Speaker 7: The link is tiny url.com/calex spectrum. Now a few of the science and technology events happening locally over the next two weeks.

Speaker 5: Rick Karnofsky [00:23:30] joins me for the calendar on the 4th of July the exploratorium at pier 15 in San Francisco. He's hosting there after dark event for adults 18 and over from six to 10:00 PM the theme for the evening is boom,

Speaker 4: learn the science of fireworks, the difference between implosions and explosions and what happens when hot water meets liquid nitrogen tickets are $15 and are available from www.exploratorium.edu [00:24:00] the Santa Clara County Parks has organized an early morning van ride adventure into the back country. To a large bat colony view the bat tornado and learn about the benefits of our local flying mammals. Meet at the park office. Bring a pad to sit on and dress in layers for changing temperatures. This will happen Saturday July six from 4:00 AM to 7:00 AM at Calero County Park [00:24:30] and Santa Clara. Reservations are required to make a reservation call area code (408) 268-3883 Saturday night July six there are two star parties. One is in San Carlos and the other is near Mount Hamilton. The San Carlos event is hosted by the San Mateo Astronomical Society and is held in Crestview Park San Carlos. If you would like to help [00:25:00] with setting up a telescope or would like to learn about telescopes come at sunset which will be 8:33 PM if you would just like to see the universe through a telescope come one or two hours after sunset.

Speaker 4: The other event is being hosted by the Halls Valley Astronomical Group. Knowledgeable volunteers will provide you with a chance to look through a variety of telescopes and answer questions about the night. Sky Meet at the Joseph D. Grant ranch county park. [00:25:30] This event starts at 8:30 PM and lasted until 11:00 PM for more information. Call area code (408) 274-6121 July is skeptical hosted by the bay area. Skeptics is on exoplanet colonization down to earth planning. Join National Center for Science Education Staffer and Cal Alum, David Alvin Smith for a conversation [00:26:00] about the proposed strategies to reach other star systems which proposals might work and which certainly won't at the La Pena Lounge. Three one zero five Shattuck in Berkeley on Wednesday July 10th at 7:30 PM the event is free. For more information, visit [inaudible] skeptics.org the computer history museum presents Intel's Justin Ratiner in conversation with John Markoff. Justin Ratner is a corporate [00:26:30] vice president and the chief technology officer of Intel Corporation. He is also an Intel senior fellow and head of Intel labs where he directs Intel's global research efforts in processors, programming systems, security communications, and most recently user experience.

Speaker 4: And interaction as part of Intel labs. Ratner is also responsible for funding academic research worldwide through its science and technology centers, [00:27:00] international research institutes and individual faculty awards. This event is happening on Wednesday, July 10th at 7:00 PM the Computer History Museum is located at 1401 north shoreline boulevard in mountain view, California. A feature of spectrum is to present news stories we find interesting. Rick Karnofsky and I present the News Katrin on months and others from the Eulich Research Center in Germany have published the results of their big brain [00:27:30] project. A three d high resolution map of a human brain. In the June 21st issue of science, the researchers cut a brain donated by a 65 year old woman into 7,404 sheets, stain them and image them on a flatbed scanner at a resolution of 20 micrometers. The data acquisition alone took a thousand hours and created a terabyte of data that was analyzed by seven super competing facilities in Canada.

Speaker 4: Damn. Making the data [00:28:00] free and publicly available from modeling and simulation to UC Berkeley. Graduate students have managed to more accurately identify the point at which our earliest ancestors were invaded by bacteria that were precursors to organelles like Mitochondria and chloroplasts. Mitochondria are cellular powerhouses while chloroplasts allow plant cells to convert sunlight into glucose. These two complex organelles are thought to have begun as a result of a symbiotic relationship between single cell [00:28:30] eukaryotic organisms and bacterial cells. The graduate students, Nicholas Matzke and Patrick Schiff, examined genes within the organelles and larger cell and compared them using Bayesians statistics. Through this analysis, they were able to conclude that a protio bacterium invaded UCR writes about 1.2 billion years ago in line with earlier estimates and that asino bacterium which had already developed photosynthesis, invaded eukaryotes [00:29:00] 900 million years ago, much later than some estimates which are as high as 2 billion years ago.

Speaker 2: Okay.

Speaker 4: The music heard during the show was written and produced by Alex Simon.

Speaker 3: Interview editing assistance by Renee round. Thank you for listening to spectrum. If you have comments about the show, please send them to us via [00:29:30] email or email address is spectrum dot [inaudible] dot com join us in two weeks. This same time.

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