MICROBIAL METABOLISM AND ITS INDUSTRIAL IMPLICATIONS 



Metabolic activity is a common characteristic of all forms of life, 

 but to the physiologist who is conversant with the metabolism of 

 either animals or higher plants the results of the investigations on 

 microbial metabolism must be more or less bewildering. The follow- 

 ing expose may justify this statement. 



It is a general experience in all metabolic studies that part of the 

 components of the food which enter a living cell is excreted again in 

 the surrounding medium after having undergone a chemical conver- 

 sion. It is usual to designate this part of metabolism as 'catabolism' or 

 'dissimilation', in contrast to those chemical conversions of food com- 

 ponents which lead to the building-up of cell constituents, and which 

 are summed up in the terms 'anabolism' or 'assimilation'. It is ob- 

 vious that the so-called dissimilatory processes can only be important 

 for the cell from the point of view of energy supply. In the animal 

 kingdom these energy-yielding processes are on the whole of one and 

 the same type; broadly speaking they can be characterized as the slow 

 combustion of carbohydrates, fats, and amino-acids to carbon dioxide, 

 water and ammonia. This so-called respiration process is also encoun- 

 tered in the green plants, but here in all cases the primary energy- 

 yielding process is restricted to the photochemical conversion of car- 

 bon dioxide and water to a carbohydrate. 



The situation in the microbe world is fundamentally different; here 

 we encounter a diversity of dissimilatory processes which is most im- 

 pressive, because it tends to show that Nature has not neglected any 

 potential source of chemical energy on earth as a basis for sustaining 

 life. Without aiming at completeness, I should like to give some docu- 

 mentation of this almost overwhelming diversity in microbial dissim- 

 ilation. 



First consider the system glucose-oxygen which in higher organisms 

 as a rule is converted into carbon dioxide and water. A study of the 

 way in which different micro-organisms behave towards the system in 

 question has shown that certain species also bring about a complete 

 oxidation of the glucose, but that - at least under certain conditions - 

 in other species quite different conversions of the glucose occur. Table 

 I gives a survey of various ways of oxidative dissimilation of glucose 

 as encountered in the microbe world. 



A second remarkable point is that in the bacterial kingdom numer- 



447 



