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Learn the toughest concepts covered in Microbiology with step-by-step video tutorials and practice problems by world-class tutors.

10. Dynamics of Microbial Growth

Osmolarity Factors for Microbial Growth


Osmolarity Factors for Microbial Growth

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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 saw you concentrations can actually control the direction of osmosis across a cell membrane. And so 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 hype a tonic environments towards hyper tonic environments to dilute the solution across the membrane. Now saw utes such as table salt, like N A C L, sodium chloride can actually interact with water molecules. And so when these salts like sodium chloride interact with water molecules, it makes the water molecules unavailable. And so the cell can no longer use those water molecules for the purposes in which it may need them. And so having a specific amount of salt can actually impact the growth of these particular cells. And so down below, we're going to talk about salt tolerant classes of microbes and so different microbes can have different tolerances to salt concentrations in their environments. And really there are four groups of microbes that are classifying the microbes based on their salt tolerance. And so the first group that we have are the non halo tolerance, which really cannot tolerate moderate salt concentrations at all. And so really they do not like salty environments at all. Then what we have are the halo tolerance and the halo tolerance can, as their name implies, tolerate moderate salt concentration, so not too too high, but they can tolerate some moderate levels. Like for example your skin can have salt, can provide a salty environment where halo tolerance may survive. Now the next group that we have are the halo files and halo files do require quite high levels Of salt somewhere between one and 14% salt concentrations in order to survive. And so this includes organisms such as marine bacteria that live in salty seawater and things like that. And then the fourth and final group that we have here are the extreme halo fouls which require very high levels of salt even higher than the levels of salt for halo files. So they require greater Than 15% salt concentrations in order to survive. And so if we take a look at this image down below, we're showing you a graph of the salt tolerant classes of microbes. And so notice in this graph on the Y. Axis, what we have is the cell growth rate. And so once again the higher the Y. Value is, the higher the cell growth is and the better those organisms grow. And then on the X. Axis this time, what we have is the environmental sodium chloride concentration or environmental salt concentration. And so notice that we have these four 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. And so each of these curves corresponds with one of the four groups or classes of salt tolerant microbes. And so the very first one that we have over here, this one in blue, which will notice is that these are the non halo tolerant organisms and so they cannot really tolerate salt at all. And so notice that they are only able to survive or they survive best. Their highest growth rate is when there's pretty much 0% salt concentration. And as more and more salt starts to get added. Noticed that they cannot survive in salty environments. Uh Then what we have next is this orange curve right here and the orange curve is referring to the halo tolerant organisms which again can tolerate moderate levels of salt and so notice that they can grow best uh in regions where there is like salt water, for example where the salt concentrations are somewhere between Around three or 4%, something like that. And um notice that as the salt concentration start to get above 10 ISH, that the halo tolerance cannot tolerate higher levels of salt. However, the next group that we have are the halo files And the Halo files can tolerate high levels of salt somewhere between zero and 14 And so um notice that they have a optimal salt concentration that is right around 6%. And they can tolerate higher levels of salt than the halo tolerant ones. And then the last group that we have over here are going to be the extreme halo files and the extreme Hello files noticed they only grow And salt concentrations that are extremely high, their optimal growth is going to be above 15% salt concentration. Uh and so these can grow in the Great Salt Lakes where there is about 25% salt concentration. And so really this year concludes our introduction to the osmolarity factors of microbial growth and the salt tolerant classes of 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.

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