Microbiology, part 21: Metabolism - Cellular Respiration - Citric Acid Cycle & Oxidative Phosphorylation

Hi. I'm Cathy with Level Up RN. In this video, we will be discussing requirements for microbial growth. This includes oxygen, temperature, pH, and osmotic requirements. And we will also be talking about important elements that are required for microbial growth as well. At the end of the video, I'm going to give you guys a little quiz to test your knowledge of some of the key points I'll be covering, so definitely stay tuned for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcards on microbial growth requirements so you can follow along with me.

Let's first talk about oxygen requirements. So different microbes will require different levels of oxygen. Obligate aerobes are organisms that require oxygen to survive and grow. So they are obligated to use oxygen. And as you can see in the test tube, they are all at the top of the test tube where there is more oxygen. Conversely, obligate anaerobes are organisms that cannot survive in the presence of oxygen. So you'll notice in the tube that they are as far away as possible from the oxygen. Facultative anaerobes are organisms that grow best with oxygen, but can survive without it. So in the test tube, you'll notice that they are mostly at the top near the oxygen because that's what they prefer, but there are also microbes in other parts of the tube as well.

Aerotolerant anaerobes are organisms that do not require oxygen for growth but are not harmed by its presence. So they basically don't care. And you'll notice in the test tube, they are distributed all over the test tube without regard for oxygen. Microaerophiles are organisms that require low levels of oxygen for growth. So these microbes need a little oxygen, but not a lot. So they're kind of like the Goldilocks of microbes. And as you can see in the test tube, they are near the top of the test tube, but not all the way at the top. And then finally, capnophiles are organisms that require an increased concentration of carbon dioxide for growth.

Now let's talk about temperature requirements. Mesophiles are organisms that prefer a moderate temperature, typically between 20 and 45 degrees Celsius. So meso means middle, and phile means loving. So these organisms love a temperature that is middle of the road. The majority of human pathogens are mesophilic. Psychrotrophs are organisms that prefer cooler temperatures, so approximately 4 to 25 degrees Celsius. These microbes are responsible for the spoilage of refrigerated foods. Psychrophiles are cold-loving organisms that grow best around 15 degrees Celsius, but they can still grow in temperatures that are under 0 degrees Celsius. So psychro means cold. And I remember this because I'm not a huge fan of cold weather. And if you put me in cold weather, I will go psycho. The difference between psychrophiles and psychrotrophs is that psychrophiles are cold-loving, whereas psychrotrophs are tolerant of cold.

At the other end of the spectrum, we have thermophiles, which are heat-loving organisms. The prefix thermo means heat, and thermophiles grow best between 50 and 80 degrees Celsius. And then hyperthermophiles are organisms that grow in extreme heat, so between 80 and 110 degrees Celsius. Examples of thermophiles and hyperthermophiles include the microorganisms that can be found in the hot springs in Yellowstone National Park.

Moving on to pH requirements now. Neutrophiles are organisms that grow best in a neutral pH, so between 6.5 and 7.5. Acidophiles are organisms that grow best in an acidic environment, such as a pH under 5.5, whereas alkaliphiles are organisms that grow best in an alkaline environment, such as a pH over 9. In terms of osmotic requirements, halophiles are organisms that require a high concentration of salt for growth. So the prefix halo means salt. Halotolerant organisms are organisms that don't require a high concentration of salt for growth but can grow in the presence of high salt. So they are tolerant of salt.

In terms of chemical requirements, there are a variety of chemical elements required by microorganisms for growth. The first is carbon, which is the basic building block of life. Carbon is the primary component of all macromolecules, including carbohydrates, proteins, lipids, and nucleic acids. Nitrogen is another important chemical element needed for microbial growth. It is required for the synthesis of amino acids, nucleic acids, and ATP. It is also a major component of chlorophyll, which is a pigment required for photosynthesis. Phosphorus is another key element needed for growth. It is needed for the synthesis of nucleic acids, ATP, and phospholipids, which make up cell membranes. Sulfur is an element required for the synthesis of amino acids such as cysteine and methionine. It is also a key component of disulfide bonds in polypeptides and is a key component of enzymes such as coenzyme A. And then finally, cells also require trace elements for enzyme cofactors. Examples of trace elements include iron, copper, and zinc.

All right. It's quiz time, and I have five questions for you. Question number one, what do you call an organism that grows best with oxygen but can survive without it? The answer is, facultative anaerobe. Question number two, what do you call an organism that cannot survive in the presence of oxygen? The answer is, obligate anaerobe. Question number three, what do you call a cold-loving organism with an optimal growth temperature of approximately 15 degrees Celsius? The answer is, psychrophile. Question number four, what do you call an organism that grows best in moderate temperatures? The answer is, mesophile. And question number five, what do you call an organism that requires a high salt concentration for growth? The answer is, halophile.

All right. That's it for this video. I hope you did great with that quiz, and I hope you found this video to be helpful. Take care and good luck with studying.

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These type of microbes are responsible for the spoilage of [inaudible]. Acidophiles are organisms that grow best.