In this video, we're going to begin reviewing the environmental factors of microbial growth. And so in this video, once again, we're only going to review information that we've already covered in our previous lesson videos. And so if you're already feeling good, then feel free to skip this video if you'd like. However, if you need a little bit of extra help, then stick around because this video could be very helpful for you. And so here in this example problem, it wants us to fill in the following blanks throughout the flowchart that's down below, reviewing all of those environmental factors of microbial growth that created these different classes.

And so over here on the far left, what we have is the classification of microbes by growth temperature. And notice that there are these 5 groups that are classifying these microbes based on their growth temperature. And so the first group that we have over here are the psychrophiles. And the psychrophiles are going to be organisms that love the cold because 'psychro' is a root that means cold and 'phile' is a root that means loving. These are going to grow between negative 5 degrees Celsius to 15 degrees Celsius in extremely cold environments. Then what we have are the psychrotrophs. And the psychrotrophs also have that root 'psychro', so they're going to also grow in cold environments. But 'trophs' is a root that means nutrients. And so these are gonna grow in cool environments such as your refrigerator, for example, which is going to have temperatures between 0 and 35 degrees Celsius.

Then, what we have next are the mesophiles. And the mesophiles also grow on me and you, as they grow in temperatures between 10 and 45 degrees Celsius, and human body temperature is right around 35 degrees Celsius approximately. Then what we have next are the thermophiles. And the thermophiles are going to grow in hotter temperatures, between 40 and 80 degrees Celsius. And last but not least, what we have are the hyperthermophiles, which are going to grow in even hotter environments than the thermophiles. They grow between 65 and 115 degrees Celsius. Next, what we have are the classification of microbes based on their oxygen requirements. And so recall that for the electron transport chain, a lot of microbes require oxygen as the final electron acceptor. And those that require oxygen are called aerobes, whereas those that do not require oxygen are referred to as anaerobes.

We've got these 5 groups here. So the first one that we have are the obligate aerobes. And obligate aerobes are going to be obligated to aerobic conditions. So they require oxygen in order to grow, and they will not grow in any other regions that do not have oxygen. Then what we have next are the facultative anaerobes. And the facultative anaerobes can grow in the presence or the absence of oxygen. However, they grow better in the presence of oxygen, and that's simply because oxygen allows for more energy, more ATP to be generated, and that allows for better and more growth. However, facultative anaerobes, they will grow in both the presence and absence of oxygen, but they grow better in the presence of oxygen. Then next, what we have are the microaerophiles, and micro is a root that means small. So these require a small amount of oxygen in order to survive.

Too much oxygen is toxic, and no oxygen is also going to not be good for them. So, it needs a small amount of oxygen. Next, what we have are the obligate anaerobes. And the obligate anaerobes are practically the opposite of the obligate aerobes because the obligate anaerobes cannot grow with oxygen. They can only grow in anaerobic environments. They are obligated to anaerobic environments that lack oxygen. Then last but not least, what we have are the aerotolerant anaerobes, and these can grow equally in, with or without oxygen. And so, oxygen is not toxic to these organisms, and they really will grow equally with or without oxygen.

Then what we have over here are the classification of microbes by the pH requirement. And so we have 3 groups here. We have the acidophiles, and the acidophiles are going to have an optimum pH of less than 5.5. So they have an acidic optimum pH. Next, what we have are the neutrophiles which, as their name implies, they are going to have an optimum pH near neutral, between 5.5 and about 7.9, close to neutral. And then, the last group that we have here are the alkalophiles. And the alkalophiles are going to have a pH that is about, or is a basic or alkali, pHs above, equal to or greater than 8.

So they have basic pHs or alkali pHs, optimum pHs. Then last but not least, what we have over here are the classification of microbes by salt tolerance. And we've got these 4 different groups here. First, we have the nonhalotolerant organisms, which do not tolerate salt concentrations. They really don't tolerate sodium chloride concentrations. So they must grow in areas that do not have salt or do not have a lot of salt concentration at all. Then what we have are the halotolerant organisms. The halotolerant organisms, as their name implies, are capable of tolerating medium or moderate concentrations of salt, such as your skin, for example. Then we have the halophiles. And once again, philes means is a root that means loving.

So these grow in high concentrations of salt between 1 and 14% sodium chloride concentration. And then last but not least, what we have are the extreme halophiles, which are going to be growing in salt concentrations that are greater than 15% sodium chloride here. So they grow in even saltier environments than the halophiles. And so, really, this is just a recap and a review of all of the information that we talked about in our previous lesson videos. And so, I'll see you all in our next video.