 Hi everybody Dr. O here. This is a super important video. I'm going to walk through the oxygen requirements of microbes. So obviously there's a ton of growth requirements that microbes have just like me, you and your children. But the oxygen requirements are a critically important one. So I want to walk through all five different types of organisms based on their oxygen requirements. I'll explain kind of why they are the way they are, why you see the test tubes the way you do here, and then I'll give you some examples. So first thing I want to start off with is oxygen is poisonous, right? Like oxygen is toxic. It leads to reactive oxygen species, which is a fancier way of saying free radicals that you've probably heard of. Oxygen causes things to rust, it causes your fruit to brown, it causes the same things to happen inside of us. So oxygen is toxic. So an organism like you and me that can deal with oxygen, it's that we actually have systems in place that we can neutralize the harmful effect of oxygen. So obviously, yes, oxygen causes a problem, but if you want to go without it, you know, try holding your breath and see how far that gets you. But that's the first thing I want you to note is that oxygen is something that has to be dealt with. It's very important, but the fact that it's unstable and leads to these problems is the reason it's so good at helping us to generate energy, but it also has a downside. You know, there are lots of theories of aging, but the free radical theory of aging is one that many people, most people believe is at least partially the reason that we age. So we need it to survive, but it does cause a part of the decaying process and which leads to mutation, etc. That leads to aging and inevitable death. All right. So first, first group is the obligate aerobes. As you can see by looking at this test tube here, they can only grow at the top. So if you're looking at a test tube, the top portion of a test tube is going to have about the same amount of oxygen as the atmosphere around us. The bottom of a test tube is not going to have any as long as it was properly prepared. And in the middle, you're going to see maybe about half as much oxygen as we'd see in the atmosphere. So as you can see by looking at this test tube, obligate aerobes, they have to have oxygen to survive. That's why they only grow at the top of the test tube. So this means that not only do they require oxygen, but they have found ways to neutralize it. So I'll have to throw some big terms here at you. But so what happens is if you're going to deal with toxic forms of oxygen, you have two main enzymes that do that. The first one is called superoxide dismutase. And it takes these toxic reactive forms of oxygen and turns it into hydrogen peroxide, which obviously needs to be dealt with. You can't have a bunch of hydrogen peroxide swimming around in your body. Hydrogen peroxide is really good at killing microbes. Our immune system uses it for that job. But we can't have too much of that around either. So the next step, once superoxide dismutase has done its job, the next step is an enzyme called catalase that actually turns hydrogen peroxide into water and in a safer, more stable form of oxygen. You've all seen this work. I actually think I have an image here. Let me jump ahead. So on the right hand side here, you see a catalase positive organism causes that bubbling. So if you put hydrogen peroxide in an organism and you see it bubble, that's actually the enzyme catalase neutralizing that hydrogen peroxide. So you've all seen that if you ever put hydrogen peroxide on a wound, that bubbling is the enzyme catalase neutralizing hydrogen peroxide. So you could make an argument that it's not proof that it's working. Like when I was a kid, I thought it meant, I thought it was bacteria dying or popping or whatever when I was a little kid. It's actually evidence that the hydrogen peroxide is being destroyed by that enzyme. So all right, that's not a big deal now. But that, so we, that means that obligate aerobes like you and me, we have the systems in place to neutralize oxygen. So we get the benefit of using oxygen for our metabolism, but we also can neutralize the toxic forms of it. All right, another example of an obligate aerobes, there's not a ton of them because they don't have, they don't have a really good survival advantage. They can only live in places with lots of oxygen. But the best example that you've heard of would be mycobacterium tuberculosis, the causative agent of TB. All right, so that's your obligate aerobes. They obligate means required. They require oxygen in high amounts to survive. So me and you would fit into that category. Next, let's just go through the order here. Next, we have the obligate anaerobes. So these cannot live in the presence of oxygen. They don't have the enzymes to neutralize the toxic forms of oxygen that are created. So if you put an obligate anaerob anywhere near oxygen, the oxygen will kill it. That's what I meant about oxygen being toxic, and we just find ways to deal with it. So obligate anaerobes are only going to grow at the bottom of one of these test tubes. So the best example of your obligate anaerobes would be the clostridium. So you have anyone that works in health care, you have clostridium difficile or difficile, or CDIF, as what people call it, which causes 23, 25,000 deaths a year. It's a very important organism to understand. Clostridium tetanus, the causative agent of tetanus, and clostridium botulinum, the causative agent of botulism. So those would be good examples of obligate anaerobes. So obligate aerobes need oxygen, only can survive in its presence. Obligate anaerobes can't tolerate oxygen, only survive in its absence. The next two you're going to see, they survive everywhere. They can grow anywhere, everywhere in a test tube. So then we have the facultative anaerobes and we have the aerotolerant anaerobes. So a facultative anaerob, it prefers oxygen. It wants oxygen to be around, which is why you're seeing the most growth at the top of the test tube, but it doesn't need it. So it can actually grow without it. So if oxygen is available, it will grow better. But if oxygen is not available, it can still survive. So that's a facultative anaerob. Lots of big, important examples here, E. coli, staff, strep, those are all examples of facultative anaerobes. They want oxygen, but if it's not around, they can still survive. And that's why they have a huge advantage over the obligate aerobes that can only survive if there's lots of oxygen. Next, we have the aerotolerant anaerobes that I think the name is very helpful here. It tolerates oxygen, but it's an anaerob, which means without air, without oxygen. So it does not use oxygen, but it can tolerate its presence. So notice the test tube. It grows evenly throughout the test tube because it's not using oxygen. If there's some there, it can deal with it. It can neutralize it. If there's none there, it doesn't matter because it doesn't need it. So aerotolerant anaerobes don't use oxygen, but can grow in its presence. So the best example here would be like the lactobacillus that would be in your yogurt, some of your probiotics, the lactobacillus, the lactic acid producing organisms, they are aerotolerant anaerobes. And lastly, we have the micro-arrow files. So like the name implies, files means to love. They love a little bit of air. So micro-arrow files, they're not going to grow at the top of the test tube. There's too much oxygen there, and they don't have, they have some of the enzymes to neutralize the toxic forms of oxygen, but they can't neutralize that much of it. So they can't grow at the top of a test tube where you see a lot of oxygen. They can't grow at the bottom because they do need oxygen. They're going to grow somewhere in the middle. I wish this picture had it growing a little bit lower, but the micro-arrow files, they need and can tolerate a little bit of oxygen. The name's pretty helpful there too. Let's see. Good examples of the micro-arrow files would be helicobacter pylori. So it grows in your stomach where there's a little bit of oxygen. And then the campylobacter, which they're a big problem with, you can get campylobacter infections from poultry and dairy, those kind of things. So another one more thing to note here, the micro-arrow files, they're also called capnophiles. So capnophiles, that means they love carbon dioxide. So micro-arrow files don't like a lot of oxygen, can't tolerate much of it, but they grow in the presence of carbon dioxide really well. All right, I'm just going to see if I have, I already showed you the catalase image here. This would be an example of anaerobic chambers, where if you're going to grow organisms that can't survive in the presence of oxygen, you would put them in something like this. And nothing really to see there. So all right. So those are, I'll go back to the first image there. So these are the five different types of microorganisms based on their oxygen requirements. So I hope this is a huge help. This is a very important topic. Watch this video again. Have a wonderful day. Be blessed.