Biology: The Archaea

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So I want you to think about this. I've got you absolutely convinced that we've got to flush that cosmic toilet and get rid of all the classification schemes we've made before. Let's think about a three-domain system. We keep talking about the new systematics, and so now let's look at the archaea together. But before we do that, I want to talk to you just one more time about why we've taken the archaea and separated them out from the bacteria. What's so special about archaea?
Well, there's a lot of things. I'll tell you a few of them. First of all, you have to understand the position systematists have been in. Here we have these one-celled things. We call them all prokaryotes. That's a descriptive term and so we needed a kingdom name. So we said "monera." We said, "monera, that's the bacteria, and maybe the blue-green algae, but who knows?" It was like this real head-scratchy kind of thing. And then they started to investigate, and you know that they investigated DNA sequence and the whole new field of systematics is going that way. But there's more to that. Some of these bacteria were just so darned bizarre. Bacteria that could live in boiling water-water greater than 100 degrees. Bacteria that could live in acid, bacteria that could live in salty concentrations that should take a cell and just shrivel it up. So the whole idea of taking these bacteria and putting them together is something no one had ever thought about before until we started to look at some evidence. Well, what are some of those evidences?
Well, certainly we've sequenced some of their DNA. And you know by now, I'm sure, that ribosomal RNA-you remember that eukaryotes aren't the only things with ribosomes. Prokaryotes have ribosomes, too. Ribosomal RNA is fairly small hunks of nucleotides that can be easily sequenced, and our studies of ribosomal RNA have shown that this group I'm about to tell you about really is different than the other bacteria. But that's not all. They also did their genome and they found out that this group I'm about to tell you about, this whole group called archaea, was pretty different than the other bacteria. How different was it? Well, in one group they found 1,738 genes. Is that a lot of genes? Well, it depends. It's all relative. But they found this many genes, and what they found out is that about half of those genes were unique to the archaea. Fifty percent of their genes were different than bacterial genes. And the archaean, these things that we say, "Okay, you're an archaean, you're an archaean, you're a bacteria," shared many of these unique genes. So we have literally DNA sequences that are correlated.
There's other stuff, too. Some membrane things are bizarre. I know you remember about Phosphatidyl Choline. If you remember that, that's a membrane lipid. It is the membrane lipid. It turns out that unique to these things we're going to call archaea are a special kind of membrane lipid. Some of them are so bizarre that they have two... For example, look right here. If you've ever learned about cell membranes, which I know you have, you know that you've got a lipid bi-layer. On the other hand, the archaea have some lipids that have literally glycerols at both ends. Now, if you remember your lipid biochemistry, you remember that a Phosphatidyl Choline had a glycerol molecule at one end, and we had our two little chains, our fatty acid chains, coming off of that. These particular ones you're seeing-glycerols at two ends. Very bizarre. And guess who's the only one on the whole planet with those? Yep. Archaea. Everything we're deciding to call archaea.
Last, but not least, there's a very important membrane chemical that bacteria have called peptidoglycans. Guess what? Archaea, they don't have them. So is my case made? There seems to be a group of bacteria that are strange. Now that I've whetted your appetite, let's talk about these rather odd things.
There's four groups. How new is this? We don't even know what to call them. I'm calling them "groups." Usually you say "divisions" or "phyla." We'll come back in a couple of years and we'll have a name for them. We want to start out with the methanogens. The methanogen is the first group of archaea. See the word "methane" there? Methane gas. All of the methane on our planet seems to come from methanogens. What they do is they have a slightly different process than many organisms. They do a process where they literally make methane. There's a lot of different words for methane, some of which we can use and some we can't. We'll just call it "marsh gas." What other forms of gas are known to contain methane? And usually methane doesn't smell all that good... Anyway, what happens with methanogens is they literally make this gas, methane, just almost like a photosynthetic organism would use that and would do photosynthesis, and instead of making organic materials, like glucose, this thing is going to make methane.
These things are so bizarre that they're poisoned by oxygen. Oxygen is a poison. Bad news if you happen to live in an oxygen environment, but they tend to live in swamps. They tend to live in places where you don't find a lot of oxygen. There's a whole group of these things that live in the guts of herbivores. You know why cows can eat grass and you and I can't. It's because they have an extra portion of their digestive system that has methanogens in it and they generate methane all the time. Someone has done a study that says we can actually power cities with the gas given off by cattle because they're constantly producing methane by these methanogens.
Termites-how come termites can eat wood? You want to know why termites can eat wood? You think they can digest that wood? No. They have a protozoan living inside of their gut. You think that protozoan can digest wood? No. Inside the protozoan-guess what? There's a methanogen. Without that the wood can't be digested. So ecologically I hope I'm showing you some things, too. Let me tell you a couple of more here.
Another one is called the extreme halophiles. Philic means loving. They love salt. These things live in places where most other organisms couldn't live. They are unbelievably salt tolerant. For example, the Great Salt Lake. In fact, many of these live in environments that are-the Salt Lake isn't this way-but that are ten times saltier than sea water. I don't want to stop here, but I want to diverge a little bit. You're starting to get the idea that these branch off from the bacteria later, and what they did was they actually could occupy niches that other organisms couldn't exist in. And so ecologically and evolutionarily, we've got something in a situation where there's no oxygen, anything else isn't going to be able to survive there, the methanogens could. There's this niche available with this incredible saltiness, vis-à-vis, the halophiles could.
How about thermophiles? What do you think they live in? The extreme thermophiles are heat loving. These are amazing. These things can live in water up to 105 degrees Celsius. For example, hot vents in the sulfur springs. I'm sure you recognize these. These are the giant tubeworms discovered by Robert Ballard back, I think, in the `70's, down at the bottom of the ocean. What we found down there were entire ecosystems that no one suspected survived or even existed. And why do we not suspect they existed? Because they're nowhere near light, and yet these things survive. These are tubeworms. These are worms that are feet long. We're not talking microscopic. They're feet long. How could a worm be this long? You know what was even more amazing? They don't have a mouth and they don't have a gut. They depend on thermophiles living in a symbiotic relationship with them that actually do synthesis for them and absorb their food. And how hot is it down there? It's unbelievably hot down there. These things can live down in this thermophilic condition. I mentioned the sulfur springs. These things in sulfur springs can actually-they'll get their energy from the oxidation of sulfur and sulfur compounds. So there's a niche, an ecological niche.
So what do we have? We have extreme halophiles, we have extreme thermophiles. We have methanogens. Well, one more. This one is so bizarre that it's the only genus of this think we've ever found. It's called thermoplasma. That's a genus name. So this thing has been classified probably before anybody knew it was an archaean. This thing is not only thermophilic, it's acidophilic. Now, acidophilic means acid loving, and to a degree all of them are. This particular one is found in coal deposits.
So I want you to think about the archaeans. This is a very strange group of things. We're talking about things with strange biochemical differences. We're talking about things that live places most organisms would never choose to live. Would you like to live in the stomach of a cow? I don't think so. Or in a worm at the bottom of the sea? Or in the Great Salt Lake? And yet, it just goes to show you that no matter what, life will take advantage of any niche given to it as it improves upon an existing condition. Archaea are no exception.
The Evolution of Life on Earth
Domain Archaea
The Archaea Page [1 of 2]