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VUMIE Bacterial Physiology:  Sugar Metabolism

Microbial metabolism is always studied from the perspective of the use of sugars to generate energy.  Part of the reason for this is because sugars are common in nature.  Glucose and fructose and sucrose are all sugars made by plants as products of photosynthesis and metabolism.  They are used to fuel cell metabolism once the sun goes down.  Likewise, sugars are the fuel used by muscle, meaning a ready supply is always found in the bloodstream.

There are MANY different sugars, some with 4, 5, 6, or even 7 carbons.  The enzyme pathway we call glycolysis is actually one of several collections of enzymes that work together making small changes to convert the sugars into end products like pyruvate (pyruvic acid).  Getting the various sugars to that end molecule involves glycolytic pathway enzymes making a series of small changes, taking out molecule parts, making rearrangements of the atoms present, and deriving some energy along the way.

As parts are removed from the sugars, acidic molecules are often generated (like pyruvic acid, for instance).  These acidic products can be detected using pH indicators to show increased acidity in the culture medium.  So, it is possible to determine whether a specific sugar has been metabolized by the glycolytic pathways of an organism by giving it that sugar in a sterile growth medium at neutral pH and then looking for a pH change following growth.  If the sugar is not used by the microbe, no acids are produced and the pH does not drop.  This is at the heart of all sugar tests used in microbiology.

To explore this in greater detail, go to VUMIEtm 2012 and follow the directions in MDM Exercise 12 "Carbohydrate Fermentation Tests" (sugars are simple carbohydrates).  Your instruction will clarify what documentation should be turned in - Virtual Lab Report, MDM Exercise 12, or other.

When this has been completed, you may be asked to take a quiz over sugar metabolism.