Chemosynthetic Symbioses: Living Together Can Be Fun

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00:00:07.13 Hi. I'm Colleen Cavanaugh.
00:00:09.21 I'm a professor in the Department of
00:00:11.14 Organismic and Evolutionary Biology
00:00:12.28 at Harvard University,
00:00:14.16 and the Co-Director of the
00:00:16.07 Microbial Sciences Initiative.
00:00:18.08 Today, I'm going to tell you about
00:00:20.07 the discovery of chemosynthetic symbioses.
00:00:22.14 These are intimate associations between
00:00:24.23 bacteria and marine invertebrates
00:00:26.28 that allow both partners to
00:00:29.05 colonize and thrive
00:00:30.27 in otherwise inhospitable environments.
00:00:32.17 The discovery of these symbioses
00:00:34.05 followed on the discovery of
00:00:36.11 the deep-sea hydrothermal vents
00:00:37.27 and the communities that flourish around these.
00:00:40.25 But finding the symbioses at the vents
00:00:43.21 also highlighted that
00:00:46.05 these occur in other habitats,
00:00:47.25 such as coastal sediments
00:00:49.24 that have a lot of sulfide.
00:00:51.05 So, today, what I'm going to do is
00:00:53.13 first provide you with some background on symbiosis,
00:00:55.23 on chemosynthesis
00:00:57.16 -- the basis of these symbiotic associations --
00:01:00.04 on the hydrothermal vents,
00:01:01.20 and then on my academic path through this adventure.
00:01:06.20 So, symbiosis, the term,
00:01:09.17 was coined by Anton deBary
00:01:11.07 to mean the living together of differently-named organisms.
00:01:15.23 These are associations with benefit
00:01:18.12 to at least one of the partners,
00:01:20.04 and as examples,
00:01:21.23 there are corals,
00:01:23.04 which have intracellular photosynthetic algae that feed them;
00:01:25.18 legumes that form symbioses
00:01:27.23 with nitrogen-fixing bacteria
00:01:29.19 -- so, effectively, they're self-fertilizing;
00:01:31.19 chloroplasts and mitochondria
00:01:34.22 in our cells and plants,
00:01:36.12 which evolved from free-living bacteria;
00:01:38.10 and of course, recently,
00:01:40.00 we know about the human microbiome,
00:01:42.19 there's been a lot of work in the last 7-8 years,
00:01:45.14 and the impact that your own bacteria,
00:01:49.06 those within your gut, on your skin,
00:01:51.04 and all over your body,
00:01:52.29 have on development of your immune system,
00:01:56.06 nutrition, neurobiology...
00:01:58.04 the list goes on and on.
00:02:00.05 So, symbiosis is an
00:02:03.07 incredibly important aspect of biology.
00:02:10.02 So, the common theme, here, for these symbioses,
00:02:13.06 and one of the main processes,
00:02:15.10 is CO2 fixation.
00:02:17.07 Carbon fixation is...
00:02:19.12 typically, we think of it by plants,
00:02:21.19 which is via photosynthesis.
00:02:24.00 This is taking carbon dioxide out of the air
00:02:25.23 and turning it into sugars,
00:02:27.17 and in plants you use light to fuel that operation.
00:02:31.00 In bacteria that are capable of chemosynthesis,
00:02:37.10 they use inorganic compounds,
00:02:38.02 such as hydrogen sulfide, iron, hydrogen,
00:02:40.14 and oxidize these compounds to produce the energy
00:02:43.11 that is then used to fix CO2
00:02:45.09 in the same processes as photosynthesis.
00:02:49.03 Deep-sea hydrothermal vents
00:02:52.05 are ecosystems on the sea floor.
00:02:53.09 They were discovered in 1977,
00:02:55.14 in association with the search and study
00:02:58.18 of seafloor spreading.
00:02:59.28 Essentially, these are hot springs
00:03:02.03 that are associated with volcanic activity,
00:03:05.15 along the ocean ridges.
00:03:07.09 You can see in the top photograph
00:03:09.15 that these ridges circle the Earth
00:03:12.25 like seams on a baseball.
00:03:14.08 These are areas where the sea floor is spreading,
00:03:16.02 there's a lot of volcanic activity.
00:03:18.07 Sea water percolates down into the deep ocean...
00:03:22.11 or, the subfloor...
00:03:24.19 is heated, chemically charged with compounds,
00:03:27.06 and then is forced up through other fissures,
00:03:29.20 as you can see on the bottom photo
00:03:32.18 with the so-called "black smoker",
00:03:34.16 and, around these communities,
00:03:36.06 around these vents,
00:03:38.03 are these lush communities of
00:03:40.11 tube worms, clams, mussels, shrimp,
00:03:43.18 with biomass that rivals that of the rain forest.
00:03:47.12 This totally revolutionized our perceptions of life
00:03:50.16 in the deep sea.
00:03:51.24 Typically, it was thought to be
00:03:53.12 very, very sparse, because food from the surface
00:03:56.05 -- photosynthesis --
00:03:57.17 wouldn't make it down, and this...
00:03:59.20 so, it was really, how is this working?
00:04:01.26 Bringing up samples of sea water
00:04:03.16 on some of the first cruises by geologists,
00:04:05.03 they noted that it smelled very strongly of hydrogen sulfide,
00:04:09.12 and it was proposed that bacteria
00:04:12.04 using such compounds
00:04:14.00 could be the base of the food chain here,
00:04:16.13 via chemosynthesis.
00:04:19.01 As you'll see from the rest of the talk,
00:04:20.19 in addition to free-living bacteria
00:04:22.23 supporting these ecosystems,
00:04:24.01 symbiosis is prevalent and in fact
00:04:28.10 the dominant form of carbon fixation at the vents.
00:04:32.08 So, my path to chemosynthesis
00:04:35.04 and symbiosis in the deep sea
00:04:36.17 started at the University of Michigan.
00:04:38.29 I'm from Detroit and went to Michigan,
00:04:41.13 and there was a marine ecology
00:04:43.20 offered at the Marine Biological Lab,
00:04:46.06 by three Michigan professors,
00:04:47.25 it was a Michigan course.
00:04:48.28 We had two...
00:04:51.12 we had two weeks of lectures
00:04:53.01 and then had to design our own project,
00:04:54.23 and to me it was incredible that
00:04:57.06 I learned that not everything is known,
00:04:59.14 that textbooks aren't always right,
00:05:01.17 and I fell in love with research,
00:05:04.16 and I fell in love with Woods Hole,
00:05:06.18 and managed to work out so that
00:05:09.27 I could come back after graduating at Michigan.
00:05:15.10 Then I worked at the Ecosystems Center, with John Hobbie,
00:05:18.02 and during this time I was
00:05:20.03 basically in a dark room, looking in a microscope,
00:05:22.27 the whole day, all summer,
00:05:25.13 counting bacteria.
00:05:26.25 He had developed a method,
00:05:29.16 using fluorescence microscopy,
00:05:31.03 for actually being able to count bacteria in the real world
00:05:35.08 that are too small to be able to be seen
00:05:37.08 with a light microscope,
00:05:38.18 so it was a very revolutionary period of time
00:05:40.19 on the numbers of bacteria in the world.
00:05:43.25 I then went to Harvard, to graduate school.
00:05:46.28 My plan was to work on
00:05:48.26 coastal and open ocean nutrient cycling,
00:05:51.08 as this was part of the research
00:05:54.12 that I was doing when I was in Woods Hole.
00:05:56.02 So, this brings me to Harvard.
00:06:00.02 As a first-year graduate student,
00:06:02.02 I was taking a class called
00:06:04.10 Bio 255: Nature and Regulation of Marine Ecosystems.
00:06:09.03 It was basically professors...
00:06:12.01 three professors that offered it,
00:06:13.21 they talked about their own research,
00:06:15.12 and then they brought people in to
00:06:18.04 talk to the students.
00:06:19.10 And because the vents had only been discovered recently,
00:06:22.06 we had a series of talks on them,
00:06:25.12 and the first was on the ecology, by Ruth Turner,
00:06:27.24 a professor in my department,
00:06:29.06 the second was on chemistry, by Russ McDuff,
00:06:32.19 who was a chemist at MIT working on vents,
00:06:35.28 the third was on microbiology.
00:06:38.06 Holger Jannasch was from Woods Hole,
00:06:39.15 from the Woods Hole Oceanographic Institute,
00:06:41.23 I knew him there,
00:06:44.03 and he talked about the presumed microbiology,
00:06:46.13 chemosynthesis being the base of the food chain,
00:06:48.22 and a lot about sulfur bacteria, iron bacteria,
00:06:52.05 and many others.
00:06:53.17 Last, we had Meredith Jones,
00:06:56.01 the curator of worms from the Smithsonian Institution.
00:06:59.20 He came, and he was basically
00:07:02.14 a histologist and a taxonomist,
00:07:04.05 and in class he described
00:07:07.17 these tube worms, seen in this picture,
00:07:10.02 which can get up to over a meter in length.
00:07:13.09 And it turns out, very peculiarly,
00:07:17.00 they did not have a mouth of a gut.
00:07:19.19 And so the big question was,
00:07:21.23 how do they feed?
00:07:23.02 And, essentially, their smaller relatives
00:07:25.17 that could take up dissolved organic carbon
00:07:27.25 across their epidermis,
00:07:32.06 but these were so big,
00:07:33.13 it was thought the surface-to-volume ratio was much too small,
00:07:35.08 and the concentration of organic carbon at these vents
00:07:37.01 was low.
00:07:38.12 So, amazingly,
00:07:41.04 he was basically describing the tube worm
00:07:43.09 section-by-section,
00:07:44.28 through a one-meter tube worm,
00:07:47.28 and I was still awake when
00:07:51.06 he came to this slide,
00:07:54.01 and this is the so-called trophosome tissue.
00:07:57.14 This is the tissue that fills
00:07:59.24 the coelomic cavity of these tube worms.
00:08:01.22 It's a brown spongy tissue.
00:08:04.21 It was named trophosome
00:08:06.23 in previous descriptions
00:08:08.19 because it has the gonads embedded in it,
00:08:10.18 and the tissue was thought
00:08:13.13 to feed the developing eggs and the developing sperm.
00:08:15.08 So, he mentioned...
00:08:17.14 he showed this picture in the...
00:08:19.08 during the talk,
00:08:21.06 and if you look in the back
00:08:23.10 that's a millimeter ruler, so this is a regular photograph,
00:08:25.05 and he mentioned that
00:08:28.18 he saw all these crystals, and he had them analyzed,
00:08:31.14 and it turned out they were pure elemental sulfur.
00:08:34.02 It was at this point where I
00:08:37.24 jumped up and said, "Well, it's perfectly clear!
00:08:40.02 They have a symbiotic association
00:08:42.13 with these chemosynthetic bacteria
00:08:44.02 that live inside of them,
00:08:45.26 and then they feed the animal,
00:08:48.07 just like dinoflagellates,
00:08:50.12 the algae and corals, feed their corals."
00:08:53.03 He said, "No, no, we think it's a detoxifying organ."
00:08:57.09 And I said,
00:08:59.16 "Well, that's perfect, because
00:09:00.24 these bacteria can oxidize sulfide to elemental sulfur
00:09:03.02 and render it less toxic, or not toxic,
00:09:06.12 and can still fix CO2 and feed the tube worm."
00:09:10.29 So, after the talk,
00:09:14.01 I was able to convince Dr. Jones
00:09:15.16 to send me some tissue,
00:09:16.26 and that I would prove there were bacteria there.
00:09:20.01 Indeed, I thought it was a done deal,
00:09:22.18 I thought it was a given,
00:09:24.07 but I had to actually go through...
00:09:26.09 jump through many hoops to try to prove
00:09:28.07 that there were bacteria in this tissue.
00:09:29.22 Now, I might mention
00:09:31.18 I had never had a microbiology course,
00:09:33.17 and I had worked for John Hobbie almost...
00:09:36.26 well over a year-plus,
00:09:39.01 so I had a love of bacteria,
00:09:40.21 but I was looking at...
00:09:42.11 the majority of which could never be cultured,
00:09:43.27 so I was really jumping in at a basic level.
00:09:48.26 I had done scanning electron microscopy,
00:09:50.27 which is a method to
00:09:53.19 be able to look at tissues at higher magnification.
00:09:55.09 And you see on this higher...
00:09:57.07 this upper figure,
00:09:58.27 this is a scanning EM of the trophosome tissue,
00:10:02.10 which is very lobular,
00:10:04.26 and what I did was took a piece of tape
00:10:07.00 and pulled off a little bit of the surface,
00:10:10.28 and if you look closely
00:10:13.06 you'll see that it looks like...
00:10:15.16 the bottom figure, is what it is...
00:10:16.26 basically, it looked like lots of grapes to me,
00:10:20.10 large-type spheres,
00:10:22.20 and I was so disappointed
00:10:24.21 because I was used to looking at tiny little things
00:10:26.13 that were bacteria,
00:10:27.28 and I was like, "Oh, my goodness, these are huge...".
00:10:29.20 The... basically, the scale bar at the bottom is
00:10:33.07 10 microns,
00:10:35.05 so they're about 2 or so,
00:10:36.29 and I was used to looking at 0.4 micron bacteria.
00:10:40.03 I did... I talked with Holger Jannasch at WHOI
00:10:43.05 (Woods Hole Oceanographic Institute) about this,
00:10:45.23 and he did point out that symbionts...
00:10:48.19 first... oh, let me show you...
00:10:50.12 first, I did find a couple rods,
00:10:52.12 so it was promising...
00:10:54.21 a little, but only a couple.
00:10:56.23 I then talked with Holger Jannasch and he explained that
00:11:00.05 many times, bacterial symbionts,
00:11:01.13 when they're intracellular,
00:11:03.14 they lose their cell wall,
00:11:05.11 because they're osmotically protected,
00:11:06.25 and so they can have very weird shapes
00:11:09.23 or even just balloon to spheres.
00:11:13.13 So, I had hope.
00:11:14.25 In addition, we looked...
00:11:17.23 where the blue arrows are
00:11:20.22 show what looked like delineations of the host cells,
00:11:23.17 and that we inferred...
00:11:25.10 we were testing whether they were actually
00:11:27.07 intracellular or not, as well.
00:11:28.25 So, another line of evidence
00:11:31.00 that I went after, next,
00:11:33.06 was examining whether these spheres
00:11:36.05 had DNA,
00:11:37.21 and to do this I used
00:11:40.05 epifluorescence microscopy by using a stain called DAPI,
00:11:42.21 and this brings me back
00:11:45.15 to my work with John Hobbie .
00:11:46.24 So, I thought, if these spheres had DNA,
00:11:48.08 then I would have another line of evidence.
00:11:50.18 And indeed, as you can see in my notebook,
00:11:52.22 these are how I did all of my microscopy,
00:11:56.02 which is by drawing,
00:11:58.04 you can see these spheres,
00:11:59.22 and I had notes that they're about 1-2 microns... 2 microns...
00:12:03.14 and that they stain with DAPI,
00:12:04.23 indicating that they have DNA.
00:12:06.17 So, this is another line of evidence.
00:12:09.02 I also, to control...
00:12:11.12 to check the size,
00:12:12.20 took a scraping of my cheek cell,
00:12:14.26 which you see in the lower side of this notebook page,
00:12:17.03 and it turns out that the nuclei were
00:12:20.16 about 10-12 microns,
00:12:22.01 so I had another line of evidence that these things,
00:12:24.18 the "grapes", were bacteria.
00:12:26.23 But some of the more definitive work
00:12:29.17 came with transmission electron microscopy.
00:12:31.13 This is where you take thin sections through tissue,
00:12:34.06 and it actually shows the ultrastructure
00:12:36.06 of the internal organelles and organs,
00:12:40.08 and, indeed, these looked like bacteria.
00:12:42.05 So, the bacteria are labeled "b"
00:12:44.26 in this slice through the trophosome,
00:12:47.17 and they have a typical size and morphology,
00:12:49.24 and if you look at the panel on the right,
00:12:52.07 they have the typical cell envelope of Gram-negative bacteria
00:12:54.18 -- those inner two lines --
00:12:56.05 and then an outer membrane
00:12:57.19 that's inferred to be that of the host,
00:12:59.19 indicating that they are within the cytoplasm,
00:13:03.00 but separate.
00:13:04.20 So, taken together,
00:13:06.17 all of these data, along with work by other researchers,
00:13:09.15 which had shown that there are
00:13:11.21 enzymes associated with chemosynthetic bacteria
00:13:13.23 in the trophosome tissue,
00:13:15.18 and other data,
00:13:17.05 we concluded that this is
00:13:19.01 a symbiosis between these giant tube worms,
00:13:20.26 and that they form associations
00:13:23.14 with sulfur oxidizing chemosynthetic bacteria.
00:13:27.11 They have not yet been cultured.
00:13:29.02 They fall within the gammaproteobacteria,
00:13:32.04 determined by DNA sequencing.
00:13:34.06 And there has been lots of research on these,
00:13:36.20 which I hardly suggest you look at.
00:13:39.29 In general, they're shown to have
00:13:42.10 many, many adaptations to this symbiosis,
00:13:44.21 which include, of course,
00:13:46.06 being mouthless and gutless
00:13:47.26 -- they're being fed internally --
00:13:49.04 but also biochemically.
00:13:50.14 That red you see in the plume is a hemoglobin,
00:13:53.24 and it's unique in that it binds
00:13:55.19 sulfide and oxygen in separate locations.
00:13:58.13 Our hemoglobin is poisoned by sulfide,
00:14:02.16 but here they manage to deliver both compounds
00:14:05.20 to the bacteria, separately.
00:14:10.07 So, given this sort of symbiosis,
00:14:13.15 and the benefits accrued to both
00:14:15.08 -- it's a nutritional symbiosis,
00:14:17.12 the worms get internal nutrition,
00:14:20.06 they're able to live in areas
00:14:24.04 that they don't need photosynthetic food,
00:14:25.19 and the bacteria get rich...
00:14:27.25 I have, with my bacteriocentric point of view...
00:14:30.01 benefit because they
00:14:32.29 get compounds for energy generation
00:14:34.21 from both anoxic and oxic environments.
00:14:37.22 At vents, the sulfide is produced geothermally,
00:14:40.10 but the oxygen is in the overlying seawater.
00:14:43.04 And the... by colonizing an animal,
00:14:46.15 coevolution, adaptations...
00:14:49.07 the animal is bringing the sulfide and oxygen to these bacteria.
00:14:52.27 Given the benefits for both,
00:14:55.21 I would predict, and did,
00:14:57.14 that these would be everywhere,
00:14:59.01 not just at vents, but in sediments also...
00:15:02.18 like, muds, that have sulfide.
00:15:04.10 So, you can imagine my delight
00:15:06.05 when a paper was published in May,
00:15:08.24 only two months after I started work on the tube worms,
00:15:11.22 entitled "Gutless Bivalves".
00:15:14.03 They must have chemosynthetic symbionts,
00:15:16.28 they were mouthless and gutless,
00:15:18.24 and they live in sulfide-rich muds.
00:15:21.15 And there was a conjoiner in Woods Hole,
00:15:23.26 right off the coast.
00:15:26.02 I had already planned to be in Woods Hole that summer,
00:15:29.03 working on another project,
00:15:30.05 but I completely switched
00:15:33.01 and moved down,
00:15:35.01 and I had another fortuitous event,
00:15:37.19 and that is that Holger Jannasch's
00:15:40.02 microbial diversity course,
00:15:41.10 at the Marine Biological Lab,
00:15:42.21 was focusing on sulfur, because of the vents,
00:15:46.12 and he had the sulfur microbiology dream team,
00:15:50.11 which included, of course,
00:15:51.24 Holger, Gijs Kuenen,
00:15:53.21 Yehuda Cohen and Jan Gottschal.
00:15:56.24 And, effectively, I moved in to learn about sulfur bacteria.
00:16:02.07 And, as you can imagine,
00:16:06.00 I was trying to figure out how to find
00:16:08.11 a 1-micron, 2-micron sized bacterium
00:16:12.04 inside of a 1.5-cm long animal.
00:16:14.12 It didn't have elemental sulfur as a clue where to look.
00:16:17.20 But, fortunately, Gijs Kuenen pointed out that
00:16:21.22 rubisco, the CO2 fixing enzyme of the Calvin cycle,
00:16:24.14 which is unique to plants and autotrophic bacteria,
00:16:28.27 could be used as an assay for localizing
00:16:30.27 what tissue bacteria might be in.
00:16:34.22 And, indeed, the gill tissue of these animals
00:16:36.06 had very high activities of rubisco,
00:16:39.04 as you can see in this graph.
00:16:41.03 And indeed, with transmission electron microscopy,
00:16:43.20 I was able to show that
00:16:46.09 there are rod-shaped bacteria living
00:16:48.05 within the gill epithelial cells,
00:16:51.02 and a close-up shows that they have
00:16:53.07 the typical Gram-negative cell envelope,
00:16:55.18 and these, too, are included in what appears to be
00:16:58.12 a host membrane.
00:17:00.05 Direct counts of these indicated that
00:17:02.14 there are 10^9-10^10 bacteria per gram of tissue,
00:17:05.06 and they also have enzymes
00:17:09.05 associated with sulfur metabolism,
00:17:10.12 and fix CO2 depending on various sulfur compound additions.
00:17:17.13 So, we concluded, indeed,
00:17:19.12 that this also was a symbiotic association
00:17:20.29 with chemoautotrophic sulfur bacteria.
00:17:24.08 Since then, we've done a lot of molecular characterization.
00:17:27.04 They are gammaproteobacteria
00:17:29.19 and, while there are strain-level differences,
00:17:31.11 it appears to be a monoculture,
00:17:35.04 so, again, a very specific symbiotic association.
00:17:38.09 The discovery of chemosynthetic bacteria
00:17:40.08 in the tissues of Solemya
00:17:42.22 also helps explain a rather peculiar behavioral aspect.
00:17:46.05 They produce Y-shaped burrows
00:17:50.05 and hang out right at the apex of the Y.
00:17:51.24 This had been suggested to either be
00:17:55.07 a refugium from predators
00:17:56.27 or perhaps they were gardening bacteria
00:17:59.02 within the tubes.
00:18:00.21 However, the symbiosis
00:18:02.23 explains why they would do this.
00:18:06.05 They're pumping oxygen from above,
00:18:09.05 from the overlying seawater,
00:18:10.21 and sulfide from below,
00:18:12.08 in the sulfide-rich sediments.
00:18:14.04 So, they're creating the habitat
00:18:16.03 that the bacteria need,
00:18:18.04 and flowing the sulfide and oxygen over their gills.
00:18:20.17 The bacteria fix CO2,
00:18:23.19 feed the animal;
00:18:24.27 the animal is feeding the bacteria.
00:18:26.19 So, here we had two examples,
00:18:28.10 one at the vents
00:18:30.02 and one in reducing sediment,
00:18:31.17 just coastal sediments,
00:18:33.07 and this indicated to me,
00:18:35.22 indeed, that these must be everywhere,
00:18:37.18 and it turns out that all of the major macrofauna
00:18:41.03 at the deep-sea hydrothermal vents
00:18:42.29 have chemosynthetic symbionts.
00:18:45.11 This includes the bivalves,
00:18:47.02 the vent mussels
00:18:49.15 and the giant clams,
00:18:51.01 and also shrimp,
00:18:52.19 which, instead of having intracellular bacteria,
00:18:54.29 actually have them on their surfaces
00:18:57.06 as epibionts.
00:18:58.14 Further, when I and many researchers
00:19:01.26 around the world
00:19:03.09 looked at other organisms
00:19:05.15 that live in sulfide-rich muds,
00:19:08.17 we found these symbioses with oligochaetes,
00:19:11.04 with nematodes,
00:19:12.20 and with colonial ciliates.
00:19:14.05 And, indeed, the picture that looks like a rope,
00:19:16.17 that is a nematode,
00:19:17.27 and all of the filaments on top
00:19:20.06 are actually the bacteria,
00:19:21.26 so again, these are on the outside.
00:19:24.11 So, this hopefully
00:19:28.01 demonstrated that these chemosynthetic symbioses
00:19:30.05 are extremely widespread in nature,
00:19:32.13 they occur in habitats
00:19:34.15 at the interface of oxic and anoxic environments,
00:19:37.17 such as the vents and sediments,
00:19:40.12 and all I've told you about here is the discovery phase.
00:19:43.28 There has been a lot more research continuing on these various...
00:19:49.12 various symbioses,
00:19:51.00 ranging from genome sequencing
00:19:53.05 to looking at optimal growth at deep-sea pressures
00:19:56.00 and chemical gradients.
00:19:59.01 And I'll just point out, again,
00:20:01.01 as a bacteriocentric,
00:20:02.15 given the remarkable metabolic breadth of microbes,
00:20:06.07 I predict that there will be many, many
00:20:08.23 other symbiotic associations,
00:20:10.04 not just with chemosynthetic bacteria,
00:20:12.10 but with others that have
00:20:14.07 diverse metabolisms
00:20:15.26 that would be advantageous
00:20:17.24 to animals and other eukaryotes
00:20:19.16 that cannot achieve these sorts of processes.
00:20:23.16 And, on that note,
00:20:25.07 as I challenge my students,
00:20:27.05 both in class and in the lab,
00:20:28.24 expect the discovery!
00:20:30.29 Thank you.

This Talk

Speaker: Colleen Cavanaugh

Audience:

General Public
Educators of H. School / Intro Undergrad
Student
Educators of Adv. Undergrad / Grad
Researcher
Educators

Recorded: July 2016

Talk Overview

As a first year graduate student, Dr. Colleen Cavanaugh predicted and discovered chemosynthetic bacteria living in giant tubeworms found at deep-sea vents. Using a combination of electron microscopy and biochemistry, Cavanaugh showed that the bacteria metabolized sulfur and generated chemical energy for the mouthless and gutless worms. In turn, the worms provide the bacteria with an environment rich in both hydrogen sulfide and oxygen for energy production and CO_² fixation. Cavanaugh went on to discover similar chemosynthetic symbioses in coastal bivalves and numerous other marine invertebrates.

Speaker Bio

Colleen Cavanaugh

Colleen Cavanaugh is the Edward C. Jeffrey Professor of Biology, in the Department of Organismic and Evolutionary Biology, and the Co-Director of the Microbial Sciences Initiative at Harvard University. Cavanaugh’s lab studies the symbiotic partnerships between bacteria and marine invertebrates, including those found at deep-sea hydrothermal vents, methane seeps and in coastal sediments. Cavanaugh has… Continue Reading