10. Dynamics of Microbial Growth
Measuring Growth by Biomass
Measuring Growth by Biomass
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in this video, we're going to begin our lesson on measuring microbial growth by biomass. And so scientists can actually measure microbial growth by measuring its biomass, which is really just the mass of an organism. And so the biomass can actually be indirectly determined by using an instrument known as a spectra fella Tom Attar. And so a spectra for tom Attar is an instrument that acquires light absorb inTS values. And these light absorbent values are abbreviated with the capital letter A. As you see here, and the light absorbent values can be used to measure turbidity of a liquid solution, and the turbidity is really just referring to the cloudiness of a liquid sample due to microbial growth. And so the relationships that are important to note here is the hot. That high turbidity or high amount of cloudiness in the liquid culture is correlated with a high biomass of the organisms growing in the liquid culture. And that's because all of those organisms have high bio more organisms lead to higher biomass. And more organisms lead to a more cloudy or a higher turbidity, higher turbidity in the liquid culture. However high turbidity and high biomass is actually going to correspond with a low, a lower amount of detected light and a lower amount of detected light actually corresponds with higher absorbency values. And so there are some relationships here that are important to note high turbidity means high absorbency values. And so there is a limitation to using these spectra tata motors, because the liquid culture must have a relatively high concentration of cells in the culture, uh in order for it to be cloudy enough for the microbial biomass to be detected. And so if we take a look at this image down below, we can get a better understanding of the spectrum to Tom Attar and how it can be used to determine the biomass. And so we're talking about measuring the biomass of cell cultures using a spectrum for Tom Sawyer and so the spectrum saitama is really an instrument that is going to have a light source and it's going to shine a light source at a particular specimen here, the specimen is going to be a liquid culture. And what happens is as the light shines through the specimen, some of that light is going to be scattered, some of it is going to be absorbed by the specimen and some of it is going to be transmitted and basically just go directly through the specimen. And that light that goes directly through that's transmitted can be detected by this detector and the light that is detected can be turned into an absorb its value. And the absorbency value is just going to be a value between zero and one. And so here what we have is an absorbent value of 0.08, which is a relatively low absorbency value. And low absorbency values are going to dictate low biomass. And so notice that this test tube over here is not very turbid, it's not very very cloudy, especially in comparison to this one over here on the right, which is pretty turban and pretty cloudy because it has microbial growth. This one over here on the left does not really have much microbial growth at all. And so it has lower turbidity and the lower turbidity corresponds with lower biomass. And the low biomass is indicated by having low absorbency values. Now. Over here, on the right hand side, what we have is pretty much the opposite situation. We have a test tube here, a liquid culture with lots of microbial growth in it. And so it is quite turbid. It's very cloudy because of the amount of microbial growth. So we have a high turbidity over here, and the high turbidity corresponds with more biomass, there's more microbial growth, more biomass. And so that is what's leading to the turbidity. And so notice that the light source here from the spectrum utama is shining on the specimen, but notice that not as much light is passing through and so not as much light is going to be detected. Less light detected corresponds with higher absorbency values because the specimen is absorbing more light. And so notice that we have an absorbent value of 0.41 which is higher than the absorbent value of 0.8 And so basically what we're saying here is that higher absorbency values correspond with more biomass. And ultimately what we're saying is that using the spectral Tata meter to determine absorbency values can be used to determine the biomass. And so that is another way to measure microbial growth, because the higher the biomass, the more biomass, the more microbial growth and higher the absorb its. And so this year concludes our brief lesson on measuring microbial growth by biomass using a spectra for tom Attar, and we'll be able to get some more practice on these concepts as we move forward. So I'll see you all in our next video.
Measuring Total Weight
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in this video, we're going to talk about yet another way to measure microbial growth. And that is through measuring the total weight. And so once again, another method to measure microbial growth is to use the total weight of the sample. And so in order to measure the weight, the cells in a liquid culture can be centrifuge dazed and a centrifuge is really just an instrument that looks like this one down below that is going to spin the samples incredibly fast to create centrifugal forces that will pull the cells towards the bottom of the container that they are in and helped to form what is known as a cell pellet or just a pellet at the very bottom of the tube that is being spun. Now the liquid media that remains above the cell pellet is going to be removed and the cell pellet or the pellet ID cells can then be weighed. Now the liquid that is removed here after centrifuge ation is called the super Nadin. And so if we take a look at our image down below, we can get a better understanding of measuring microbial growth by weight. And so notice. Over here, on the far left hand side, we have a tube that contains a liquid culture with microbial growth. And so we need to obtain this liquid cell culture and then take the container and place the container into an instrument known as a centrifuge, which is once again going to be an instrument that spins the sample incredibly fast to create centrifugal forces and to pull all of the cells towards the bottom of the tube to create a pellet. And so ultimately what we're doing is we are spinning the cells by centrifuge ation. And this helps to create the cell pellet at the very bottom of the tube. And so once again all of these cells that are free floating in the liquid culture in the beginning. Get pulled towards the bottom to create a cell pellet at the very bottom of the tube. And that's exactly what we see over here is the cell pellet and the liquid that remains above the cell pellet is referred to as the super Nadin. And it is carefully removed or decanted or poured out very carefully in order not to disrupt the cell pellet at the bottom of the tube. And then of course, the cell pellet is going to remain inside of the tube all by itself. And at that point, we can actually weigh the cell pellet to get its mass. And of course, prior to weighing the cell pellet here, you would have had to have weighed the tube prior uh the empty tube previous, so that you can subtract the weight of the pellet and the tube from the weight of the empty tube in order to get the weight of just the pellet. But ultimately, this process allows for obtaining the weight of the pellet and the greater the weight, the more microbial growth there is. And so by weighing cell, pellets were able to measure microbial growth. And so this year concludes our brief lesson on measuring the total weight to obtain uh to measure microbial growth, 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.
A scientist wants to determine the biomass of the bacterial populations in his experiment using a spectrophotometer. He finds that population A has a higher turbidity than population B. What does this tell us about the bacterial populations?
More light was able to pass through population B than population A.
The liquid population A is being grown in is more cloudy than the liquid population B is being grown in.
Population A has more biomass than population B.
All of the above.
If a microbiologist wishes to determine the growth of her bacterial sample without removing the bacteria from the liquid they are growing in, which method should she use?
Spinning her population in a centrifuge and weighing the bacterial cell pellet.
Using a spectrophotometer to determine the biomass of the population in the liquid.
Passing the population through a membrane filter and counting the individual cells.
None of the above, all methods require the scientist to remove the bacteria from the liquid solution.