Welcome, today we're going to talk about extremophiles, life forms that thrive in extreme environments ranging from sea vents to hot springs to sub-glacial lakes to deep, dry deserts and as we look at these different forms of life I think it will be easy to speculate that life forms like this can thrive on moons like Europa and elsewhere in space. So today we'll begin by talking about Yellowstone National Park, a place where people go to study many different forms of extremophiles and talk about some of the bacterial mats that form there. Then, we'll look at the wide range of environments where life flourishes, and then finally turn to the role extremophiles play in evolution and think about the implications of these extremophiles for astrobiology. One of my favorite lines from Jurassic Park is when Jeff Goldblum says, life finds a way, what he's talking about in the case of the movie, is how evolution finds a way of exploring the fitness landscape, so that it could maximize the ability to reproduce and survive. And we see this in nature you know, its remarkable ways that it finds ways of, modifying some of the underlying biochemistry, modifying the cell walls extremophiles as we'll see in this lecture do a wonderful job of, of pushing the limits by exploring the fitness landscape, changing the way some of the basic properties of the cell operate so that the cell can survive, and find a way to thrive in extreme environments. And, we'll see that life thrives in a wide range of extreme environments and we'll see that not just archaea but also bacteria and even sometimes eukaryotes can thrive in extremes of heat, cold, acidity, and pressure. And we'll see that life does not always require energy from the Sun. And that there'll be life forms that will draw energy from surprising sources, such as radioactivity. Now as we talk about life growing, I think we have to distinguish between life thriving and life surviving. Many lifeforms can create things like spores so they can effectively hibernate through very cold winters. So there are lifeforms that can survive at very low temperatures but can not reproduce and grow in these temperatures. And what we really want to focus on today are environments where life cannot just survive and avoid being destroyed, but environments in which life can really thrive, and I think it'll be very easy as we think about these different extremophiles, to think about how they could survive and thrive in a variety of extraterrestrial environments. And for those of you working on the assignment, the final assignment, of developing your own planet and your own solar system and perhaps thinking about what kind of life might thrive in your solar system. These extremophiles, I think will provide a helpful analogs for thinking about the range of life that could survive in different environments. So let's begin by talking about the Yellowstone National Park, a very interesting place to study extremophiles. The Yellowstone National Park is a supervolcano. The caldera of the volcano is about 60 kilometers across. So, this is, we think about it as, you know, not as a single mountain. You know, it's not a classic normal volcano with a relatively small caldera on top. It is a supervolcano, a place where a hotspot brings up a great deal of hot magma relatively close to the surface. This surface heats up water and brine in this sub-surface region and it powers the famous geysers of Yellowstone National Park. Because of these geysers, and because of the upwelling of water from deep in the ground, Yellowstone Park is a place of extreme temperatures and extreme acidities. It's a very interesting place to think about and study for extremophiles. The Yellowstone volcano, super volcano, is an incredibly powerful volcano. Many of you from the United States, who have been around long enough, may remember the famous Mount St. Helens volcano, that covered a section of Washington with ash. And if you visit, this region, you can still see the remnants of that 1980 volcano. Well that volcano was tiny, compared with some of the eruptions, from the volcano in Yellowstone. The volcano eruption, 600,000 years ago produced 1,000 times as much ash as Mount St. Helens. And the one 2 million years ago produced 2,500 times as much ash, and in fact the ash covered most of the western United States. You can see the enormous extent, almost all the way to the Mississippi River. Yellowstone, as I already mentioned, offers a very wide range of interesting environments in terms of temperature and also acidity. When we talk about acidity, we like to talk about pH. pH is a measurement of acidity. Pure water has pH of seven. As the acidity level increases, the pH gets smaller. So if we ask what's the acidity of, say, a banana, it's about pH of five. Acid rain has a pH of four. Lemon juice, a pH of two. Sulfuric acid, a pH of one. And battery acid, a pH of zero. As pH's increase above seven, we get solutions that are increasingly basic. Ammonia has a PH of 11. Bleach a PH of 13, and drain cleaner; a PH of about 14. And we usually think of life thriving, most life forms we are familiar with thrives in PH of things like six. You go look at Yellowstone and you find environments in which, what we think of as ordinary life wouldn't thrive. There are places like Nymph Creek, where you find a pH of three, temperatures of 60 degrees centigrade, and the stream very rich in sulfur, brought up from the Earth by these upwellings and geysers. And if you look at Nymph Creek you'll find it's filled of life, it has life forms like hydrogenobacter, which gets its energy by metabolizing hydrogen and hydrogen sulfide with reactions like this. It uses the, these hydrogen gases as a source of energy by converting hydrogen gas to water, this reaction provides it with sugars that enable it to thrive and grow. So you're looking here at a lifeform that doesn't require solar energy. It's living off of hydrogen gas, and keep in mind, hydrogen is the most common thing in the universe, so there's lots of that to go around. Here's a picture of one of the lakes at Yellowstone, and you can see despite the enormous temperature, these lakes are filled with life, and these lifeforms form these large bacterial maps that are incredibly colorful. Here's another picture, of one of the lakes at Yellowstone, and you can see that this is a really striking place, filled with life, thriving in extreme temperatures and acidity. Here's one, of many of the intriguing lifeforms you find at a place like Yellowstone Park, Chloroflexus Aurantiacus. You'll find it at these very high temperatures and intriguingly, this life form, which has a primitive form of photosynthesis can thrive in the light, making use of photosynthesis, photosynthesis. And that, when it's in the light it looks green, but in the dark it makes use of aerobic respiration. Its energy source is not photosynthetic, and then it's orange, and this is the same lifeform. Going from green to orange, depending on its environment, and when we look at the way photosynthesis acts, it has, it acts in a very primitive way here. This chloroflexus maybe very close to or at least closely related to one of the first life forms that made use of photosynthesis as an energy source. When we look at these thermophiles, these creatures that can survive at these very high temperatures, they have interesting properties that we can understand why they survive. They have the same DNA, the same amino acids. They have the same basic building blocks that we're used to talking about and we've discussed in the previous last few lectures. But there are some interesting differences. The cell membranes are made of special lipids, and these lipids are stable at high temperatures. Most other lipids would be destroyed. We take ordinary cells, put them in boiling hot water, the cell membranes would be destroyed. But these cells have evolved lipids that can survive these very high temperatures. They also have an extra enzyme, reverse DNA gyrase. That causes the DNA to fold in a way so that it can survive high temperatures. Otherwise, if you take DNA, our DNA, DNA of most non-thermophilic forms, expose them to very high temperatures, it will be destroyed by the heat. And, in fact we can, there are using this, there are life forms in which their DNA can survive to temperatures above 150 degrees centigrade, well above the boiling point of water at ordinary pressures. And not only can some of these extremophiles survive extreme heat, there are extremophiles that can survive extreme cold and grow in temperatures down to minus 20 centigrade. Here's another thermophile, aquifex. Aquifex is a bacteria. But when you look at its genome, and its genome has been fully mapped, about 16% of its genes are archaea-like genes. It looks like it's a transitional form, but close, between archaea and eubacteria. And perhaps aquifex, which thrives in these boiling lakes is one of the earliest forms, or at least closely related to one of the earliest forms of bacteria. The name aquifex means water creator, and aquifex has a cycle. Where it actually gains energy by creating water. A lot like the hydrogenobacter we talked about earlier. Here is a beautiful lake at Yellowstone Park. The grand prismatic lake, and you can see it's covered with these huge bacterial mats and you'll see these different mats, different colors are lifeforms that survive at different temperatures. So out here you may have lifeforms that like it at 65 degrees C and here maybe 75, and here 85, and here 95. And different life forms find the environment in which they prosper and grow here. Now, this shot here is taken in the summer when the mats are red or yellow or green. Red or orange or yellow. In the winter, these mats turn green, because there's less sunlight, and they need to form more chlorophyll, in order to gain energy, and thrive. So you see in these pictures, these very large microbial mats. So when you see these microbial mats, these are single celled organisms, right? That bacteria, that, linked together to form these very large mats. These mats are ubiquitous. If the floor of your shower seems slimy, that's because you're stepping on a bacterial mat. If you haven't brushed your teeth this morning, your teeth probably look like this, and they're covered with dental plaque. Dental plaque is a bacterial mat that's actually a very complex and rich colony of many different types of bacteria that are attacking the enamel of your teeth. And they grow fairly rapidly. So if you don't brush your teeth several times a day, bacterial plaque will build up. Clean your contact lenses. Another place where you will find bacterial mats growing are on the surface of your contact lenses. If they get too large your eyes will get infected. I know this from experience. Trust me. These mats are really fascinating. I think the view a lot of us have as bacteria, is as single cells each operating on their own. Butt what happens in these mats is, the bacteria come together, form colonies, and thrive by working together; they actually communicate, to each other. Through quorum sensing. They release chemicals into their environment. They sense the concentration of these chemicals and they respond to it, so you actually have all the bacteria working together. Communicating together in some ways, well they're single cell, operating as this huge multicellular colony that can be enormous, right? You know, these mats are very large. And these environments, are very interesting places for evolution. When you bring all these bacteria together, it's a very effective place for things like lateral gene transfer. Horizontal gene transfer. You have all these bacteria close together. You'll actually find, rates of gene transfer, that can be enhanced a thousand fold over being in some kind of dilute solution. And, you know, you can imagine these bacterial mats as really a transition in some ways, between functioning and single cell, and multi-cell. All right. We've talked, about these bacterial mats. These multi-cell things. Are they made of prokaryotes or eukaryotes? Remind yourselves what prokaryotes and eukaryotes are. Think about our discussion of microbial mats. And give me an answer and we'll be back in a minute.
