In this video, we're going to begin our lesson on oxygen requirement classes of microbes. Microbes can really be classified into 5 groups based on their requirement for oxygen gas or O2. Notice down below in this table, we're showing you the oxygen requirement classes of microbes. They're organized into these 5 groups that we have numbered 1 through 5. One thing that's very important to note here is that each of these 5 groups has test tubes. These test tubes that you see here are really special because they allow for really high concentrations of oxygen towards the top of the test tube, represented by these light blue backgrounds. As you start to go towards the bottom of the test tube, you start to get lower oxygen concentrations. At the very bottom of each of these test tubes is the lowest oxygen concentration. This is something that's very important to keep in mind as we move forward throughout the rest of this video.
The very first group that we have over here on the far left are the obligate aerobes. As their name implies, these are aerobic organisms, or organisms that are obligated to aerobic environments or environments that have high oxygen concentrations. Notice that all of the brown speckles that you see throughout here represent microbial growth. There is only microbial growth here, in the region of the test tube that has the highest oxygen concentration. Obligate aerobes cannot live without oxygen. Notice here we have an obligate arrow saying "I can't live without you" to the oxygen gas because they absolutely require oxygen gas and cannot live without the oxygen gas.
Next, the facultative anaerobes, as their name implies, can survive in both aerobic and anaerobic environments. You should notice that there are brown speckles throughout the entire test tube. However, there are a lot more brown speckles towards the top of the test tube than towards the bottom. This is because facultative anaerobes, although they can grow in both the presence and absence of oxygen, actually grow a lot better in the presence of oxygen gas. That's why there are more microbes in the aerobic region of the test tube, where the oxygen concentration is higher, and fewer facultative anaerobes in regions with lower oxygen. Notice that the microbe, where there's no oxygen, is saying "this is ok, I guess," and really, this is its second option when no oxygen is present. But when in aerobic environments where oxygen is present, the microbe says "this is amazing," and the presence of oxygen is going to be its number one option to be able to grow best. So there is microbial growth throughout the entire test tube; however, there's going to be a lot more towards the regions that have higher oxygen because oxygen allows for the generation of more ATP, more energy. More energy means more growth, and that's why they're able to grow more and better in aerobic environments.
The third group we have here are the microaerophiles. The root "micro" means small. These aerobes, microaerophiles, do not need much oxygen at all. In fact, too much oxygen is actually toxic to these microaerophiles. They require oxygen; however, they need only small amounts of oxygen because, if it's too high, it's going to be toxic to them. They grow right here in this very specific region where there's a small amount of oxygen. But notice that they're not at the very top where there's the most amount of oxygen, and they also do not grow where there's no oxygen. They do require oxygen but only a small amount of oxygen gas.
The next group we have here are the obligate anaerobes. Obligate anaerobes are practically the opposite of obligate aerobes. That's because obligate anaerobes can only survive where there is no oxygen. Oxygen is pretty much toxic to these obligate anaerobes. Notice that this obligate anaerobe is saying "get away from me," and he's got his protective shield and sword because oxygen is toxic to these obligate anaerobes. They cannot grow in the presence of oxygen. They require anaerobic environments, environments that have no oxygen, in order to grow. That's why all of the microbial growth is towards the very bottom for the obligate anaerobes.
The fifth and final group we have here are the aerotolerant anaerobes. The aerotolerant anaerobes really grow equally in oxygen and areas that have no oxygen. They grow equally in aerobic and anaerobic environments. Notice that the microbial growth is evenly distributed. They do not grow better in one or the other; they grow equally in both. So here what we're saying is that these aerotolerant anaerobes are tolerant to both oxygen and regions that have no oxygen as well. So they grow in the presence or the absence of oxygen equally.
This wraps up our introduction to oxygen requirements for microbes, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.