Microbes Must Eat 63 



to carry out their assigned functions extracellularly. Once the food 

 has been broken down to a size permitting passage through the 

 semi-permeable covering of the organism, then the absorbed food 

 is further attacked within the cell by the endo-enzymes, which 

 convert the food into an available form. A rebuilding process 

 mav also be employed by intracellular enzvmes to convert the 

 food into chemical configurations required in the metabolism of 

 the specific microbe. 



Enzymology is a complex science, and a book of this nature 

 is not intended to do much more than introduce the beginning 

 student to general concepts needed to familiarize him with the 

 underlying technics employed by single-celled, mouthless, micro- 

 scopic organisms when they are faced with the problem of obtain- 

 ing food "too tough to chew" without some preliminary breakdown. 



The action of enzymes may be influenced by many of the same 

 forces affecting other chemical reactions. Temperature, moisture, 

 acid balance (pH), presence of chemical poisons, and other factors 

 have their effect on enzymes. Enzymes are highly specific for 

 given substrates. Enzyme "A" only works on substrate "A," and 

 substrate "B" can only be attacked by enzyme "B." Since phys- 

 iological reactions determine to a great degree where organisms 

 are placed in classification schemes, it becomes apparent that there 

 is a close relationship between enzymes which initiate physiological 

 reactions and taxonomy. Higher plants have the advantage over 

 bacteria in that the former possess chloroplujU, that green pigment 

 so essential to higher plant life. Chlorophyll is another example 

 of a catalyst, where the cholorphyll is activated by sunlight to 

 allow water and carbon dioxide gas to combine into plant substance 

 in a process called photosynthesis ( putting together in the presence 

 of light). 



Much of the food taken in by bacteria must be drawn upon 

 for respiration. When free gaseous atmospheric oxygen is involved 

 in respiration, we speak of this as aerobic respiration, in con- 

 trast to ANAEROBIC RESPIRATION which iuvolvcs the breakdown or 

 re-arrangement of molecules in a food substrate as a means of 



