1-11. NUTRITION AND METABOLISM OF MICROORGANISMS
Microorganisms require food for energy and for growth. Food is required for
energy for synthetic activities, for moving, and to maintain the living state. Food for
growth is required to manufacture protoplasm. Microorganisms must have their food in
solution in order for it to pass through their cell membranes. If they are not growing in a
liquid medium, then the microorganisms will secrete extracellular enzymes that will
liquefy their food.
Enzymes are organic substances that cause chemical reactions without being
consumed in the reaction; therefore, they are called organic catalysts. They are
produced by living cells and then become independent of the cells. They are incredibly
active; e.g., one molecule of the yeast enzyme can catalyze the conversion of an
inconceivably large number of sugar molecules into ethyl alcohol; and they are very
specific, that is, they act upon only one substance. Extracellular enzymes are formed
inside the cell and diffuse through the cell wall to cause their action. These enzymes
bring about digestion in the human body and putrefaction (decomposition) in fruits,
vegetables, and meats. Intracellular enzymes are formed in and remain within the cell.
a. Characteristics. Enzymes are usually named according to the kind of
substances upon which they act or the kind of chemical reaction they produce. They
are suffixed "ase" as in the case of "carbohydrase," an enzyme that acts upon
carbohydrate. As we have already stated, enzymes are specific; thus, maltase, a
carbohydrase, is the specific enzyme that converts maltose into glucose.
b. Effect of Temperature. Within certain limits, the speed of reactions caused
by enzymes is doubled for each 18F or 10C rise in temperature. A 50 percent
reduction in enzymatic action will result when the temperature is lowered 18F or 10C.
This is referred to as van't Hoff's law or temperature quotient (known as Q10). Activity
is best at temperatures between 32-104F (0 - 40C).
c. Example of Enzyme Action. As mentioned above, enzymes can initiate a
considerable amount of activity. They initiate reactions without being consumed. For
instance, the enzyme invertase (which changes sucrose into dextrose and levulose) will
invert one million times its own weight of sugar and will be capable of more activity.
d. Similarity to Living Cells. Enzymes possess some of the properties of living
cells. Living cells are destroyed by high temperatures. Enzymes are inactivated by
high temperatures and most of them are destroyed by a temperature of 165F (74C).
Living cells have optimum temperatures for their functions, and enzymes have optimum
temperatures for their actions. The actions of living cells are slowed at low
temperatures; the actions of enzymes are retarded by low temperatures. Enzymes and
living cells both require certain pH limits for their optimum actions.