 In this video I'm going to talk about interaction examples among bacteria in microbial mats from a lake in Antarctica, Lake Vanda. So the photo that I've been using as my title photo shown here is a photo taken by Dale Anderson in Lake Vanda. This is an ice-covered lake that's in the Wright Valley, in the McMurdo Dry Valleys of Antarctica, and this lake is permanently covered with ice, at least for now. And because of the climate history of Antarctica, there are no macroscopic predators in this lake. All the fish and large worms and things that would eat bacteria mostly went extinct due to glaciation of the continent and its isolation from other continents. So in this particular lake, and a lot of them in this area, there are just bacteria and a few protists and things like nematodes that eat the bacteria. I like to use this as an example of interactions because it's what a lot of life on early Earth was like, just microbial and a much simpler food web than a lot of modern ecosystems. So all of these pinnacles, each one of these pinnacles consists of bacterial growth, and in this case on a big rock, which makes this image really beautiful. So I work with divers, including Dale Anderson and some others, and they collect some of these pinnacles for us to study how they live, and we are looking at them in terms of the communities and evaluating some of the mutualism, the mutually beneficial reactions among the bacteria, as well as the competition among them to try to understand why they form these beautiful pinnacles. So when a diver collects this pinnacle, I cut it in half. So this one is half a pinnacle, and inside we can see that there are different colors and there are different shapes to the pinnacles. And we look at these pinnacles with genetics. They are composed of cyanobacteria, and they contain cyanobacteria. These are photosynthetic organisms, and they take the light that gets through the ice and down into this layer and make organic matter. There's a certain type of cyanobacteria that tends to make these tall pinnacles, and there are also cyanobacteria in these pink and green areas on the interior, and they are different species. So there are different cyanobacteria that have different needs, and they live in different places. So the ones that form these pinnacles are the same as the ones on the outside of this pinnacle. So these two types typically have the same groups of cyanobacteria in them. In addition to the cyanobacteria, there are many other types of bacteria, thousands, possibly millions of other ones, and we can use metagenomics to understand who's actually there. Okay, so what actually happens, and I should say that this brown area down in here and in here, these two areas have no cyanobacteria. So we have a lot of possible relationships among these bacteria, and it depends on the different resources. So we have light that comes in, and the cyanobacteria on the surface get the first bit of light. Some of it penetrates in for these other bacteria to grow. So we have competition for light from the outside to the inside of the mat. We also have competition for space, like who actually grows on the surface, and what we found in studying these mats is that there are certain types of cyanobacteria that can grow on the surface and some that only grow on the interior. The ones on the exterior are also on the inside, so they can compete for that space on both the outside and inside, whereas some of the ones on the interior only grow on the interior. We also have a competition, we think, for nutrients. There are very few nutrients in the water, but in this interior of the mat, the organic matter is getting broken down by bacteria, besides that aren't cyanobacteria, and we think that it's releasing nutrients and those nutrients are diffusing into this overlying mat, hoping the cyanobacteria grow. So that's an example of mutualism. So in the case of mutualism, the cyanobacteria provide food through the photosynthesis. So the cyanos provide food for the other bacteria in the organic matter, and the other bacteria when they actually cause decay of those bacteria provide nutrients for the cyanobacteria. And so there's this mutualism that the cyanobacteria and the bacteria work together to create a cycling of important elements. And we actually know from trying to grow the cyanobacteria in the lab that they really do not grow without their bacterial friends. There's this very, very tight connection among certain bacteria and certain cyanobacteria for community to grow well. There's also another relationship, and we don't understand the full nature of it, but you'll notice that one of these columns is very skinny and the other is much fatter. So we'll move on to another image to take a look at those. Notice that one of these pinnacles is really thick and one of them is really thin. Our interpretation is that the community of cyanobacteria that grows this pinnacle is the first part of the ecosystem and then the cyanobacteria that create these colors, the pinks and greens, they colonize the interior of the pinnacles. So the interpretation is that the second process is once there's enough biomass, more cyanobacteria can grow on the inside. And we've done various studies that show that enough light actually gets to the interior that these areas that are pink inside are during photosynthesis and they're actually causing the pinnacles to swell up. So if we think about this sort of evolution of the pinnacles in terms of process, we know that the interior community benefits from the growth of the exterior one. We don't know for sure whether or not the exterior community benefits. Is it a positive? Is it neutral? With no benefit, no effect, or is it negative? We don't know how the growth of the interior community affects the exterior one. We don't think that it's negative because the exterior community is always seen on the outside of the interior one. So we think that it's actually maybe a mutual process or commensal one. We have competition for light from the exterior community and the interior community. We have competition for nutrients, but we also have mutualistic beneficial processes with bacteria causing decay of the organics, providing nutrients to the photosynthetic organisms. And we also have the creation of an environment by the exterior community that allows the interior community to grow. Even though this is a very simple ecosystem, it provides a lot of examples of interactions between species.