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Fueling in Heterotrophs – Bacteria

by Vincent Racaniello, PhD
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    00:00 Let's take a look at these three lifestyles in just a little bit more detail. Here is fueling in heterotrophs, again these are bacteria that need to acquire the building blocks.

    00:12 As you can see here the organic substrates that they require outside of the cell, they are imported into the cell by some of the transport mechanisms we talked about, so now they're in the cytosol. They get put into central metabolic pathways which are shown in color here and these include glycolysis, the TCA or the Kreb cycle and the pentose phosphate pathway. These use electron transport to generate energy in the form of NADH or ATP and precursor metabolites. The precursor metabolites then go to make the amino acids, which then are used for larger molecules. So these are examples of bacteria that need to acquire the organic substrates preformed, they can't make them. The chemoautotrophs can take inorganic ions and import them into the cell and use them to make energy by an electron flow that's in the membrane of the cell. They can also take carbon dioxide and feed that into the central metabolic pathways and make all of the precursor metabolites that they need.

    01:24 All of those chemicals that are then going to go on and make amino acids and lipids and so forth, these bacteria can synthesize, it is quite remarkable. So remember, in comparison, the heterotrophs have to import the precursor molecules that they need, these bacteria can synthesize them on their own. And finally the photoautotrophs, they use light to make energy in the form of ATP or NAD, they import carbon dioxide and they make all the precursor metabolites that they need, very much like the autotrophs, except that here light is used to make energy.

    02:00 So three remarkably different and flexible and versatile ways to build new bacteria.

    02:07 Now along with these metabolic differences, we also classify microbes according to how they respond to oxygen and I want to review that with you here. We have one class of bacteria that we called aerobes. Another way of describing these are strict aerobes, these bacteria will grow in air, but if you take away oxygen they will not grow at all. So they are strict aerobes, they need oxygen; an example is the soil growing bacteria, Bacillus subtilis. Another class is the anaerobe, also known as the strict anaerobe, it will not grow in air, if you want to grow these bacteria in the laboratory, you have to grow them in a vacuum without air. They will grow without oxygen, they don't need it and in fact it's bad for them to have it, an example of this is Clostridium botulinum, a bacterium that makes a very potent toxin, botulism toxin. We then have facultative bacteria, these bacteria can grow in air or they can grow without oxygen, they can go either way, that's why we call them facultative. An example is Escherichia coli, that common inhabitant of our intestinal tracts. We also have another class which we called indifferent, it's a funny name to give a bacteria, we also call these aerotolerant anaerobes, they will grow in air and they will grow without oxygen, an example is Streptococcus pneumoniae, the agent of pneumonia in human. Now you may wonder what's the difference between a facultative and an indifferent bacterium? Well there are other chemical differences and metabolic differences that distinguish these two. And finally we have what we call microaerophilic bacteria. These will grow a little bit in air, they don't do so well, but they do fine without oxygen, so they'd rather not have air present, but if they happen to have, it won’t inhibit their growth. An example is Campylobacter jejuni.


    About the Lecture

    The lecture Fueling in Heterotrophs – Bacteria by Vincent Racaniello, PhD is from the course Microbiology: Introduction.


    Included Quiz Questions

    1. Cell membrane
    2. Cell wall
    3. Cytosol
    4. Nucleus
    5. Flagellum
    1. Bacillus subtilis
    2. Clostridium botulinum
    3. Clostridium tetni
    4. E.coli
    5. Streptococcus pneumoniae
    1. Campylobacter jejuni
    2. Clostridium botulinum
    3. Clostridium tetni
    4. E.coli
    5. Streptococcus pneumoniae

    Author of lecture Fueling in Heterotrophs – Bacteria

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD


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