In this video we're going to begin our lesson on the osmolarity factors of microbial growth. And so first we need to recall from our previous lesson videos that solute concentrations can actually control the direction of osmosis across a cell membrane. If you don't remember this idea too much, make sure to go back and check out our older lesson videos on osmosis before you continue here. Now that being said, recall that water during osmosis will always flow from hypotonic environments towards hypertonic environments to dilute the solution across the membrane.
Now, solutes such as table salt, like NaCl (sodium chloride), can actually interact with water molecules. When these salts like sodium chloride interact with water molecules, it makes the water molecules unavailable. The cell can no longer use those water molecules for the purposes in which it may need them. Having a specific amount of salt can actually impact the growth of these particular cells. Down below, we're going to talk about salt tolerant classes of microbes. Different microbes can have different tolerances to salt concentrations in their environments. Really there are 4 groups of microbes, classifying the microbes based on their salt tolerance.
The first group that we have are the nonhalotolerants, which really cannot tolerate moderate salt concentrations at all. They do not like salty environments at all. Then what we have are the halotolerants. As their name implies, halotolerants can tolerate moderate salt concentrations. Not too high, but they can tolerate some moderate levels. For example, your skin can provide a salty environment where halotolerants may survive.
The next group that we have are the halophiles. Halophiles do require quite high levels of salt, somewhere between 1 and 14% salt concentrations in order to survive. This includes organisms such as marine bacteria that live in salty seawater and similar environments. The fourth and final group that we have here are the extreme halophiles, which require very high levels of salt, even higher than the levels of salt for halophiles. They require greater than 15% salt concentrations in order to survive.
If we take a look at this image down below, we're showing you a graph of the salt tolerant classes of microbes. Notice in this graph on the y-axis, what we have is the cell growth rate. Once again, the higher the y value is, the higher the cell growth is and the better those organisms grow. On the x-axis this time, what we have is the environmental sodium chloride concentration, or environmental salt concentration. Notice that we have these 4 different curves. We've got this light blue curve right here. Then, we've got this orange curve right here. This red curve right here. And then, we've got this dark blue curve, over here. Each of these curves corresponds with one of the 4 groups or classes of salt tolerant microbes.
In blue, notice these are the nonhalotolerant organisms. They cannot really tolerate salt at all. Notice that they are only able to survive, or they survive best, when there's pretty much 0% salt concentration. And, as more and more salt starts to get added, notice that they cannot survive in salty environments. Next is this orange curve right here. The orange curve is referring to the halotolerant organisms, which again can tolerate moderate levels of salt. Notice that they can grow best in regions where, for example, the salt concentrations are somewhere between around 3 or 4%. Notice that as the salt concentrations start to get above 10-ish, the halotolerants cannot tolerate higher levels of salt.
However, the next group that we have are the halophiles. Halophiles can tolerate high levels of salt, somewhere between 0 and 14%. Notice that they have an optimal salt concentration that is right around 6 percent, and they can tolerate higher levels of salt than the halotolerants. The last group that we have over here are going to be the extreme halophiles. Extreme halophiles notice they only grow in salt concentrations that are extremely high. Their optimal growth is going to be above 15% salt concentration. These can grow in the great salt lakes where there is about 25% salt concentration. Really, this here concludes our introduction to the osmolarity factors of microbial growth and the salt tolerant classes of microbes. 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.
