MICROBE AND LIFE 



its surroundings. It are these latter conversions that constitute the basis 

 for the energy-requiring functions of the living organism. 



In surveying the situation in green plants and higher animals from 

 this point of view the following main features can be delineated. The 

 green plant derives its energy primarily from solar radiation which 

 permits it to synthesize its cell material from the inorganic carbon 

 dioxide and a few other mineral ingredients. In contrast, life in the 

 animal kingdom has exploited an entirely different source of energy; 

 the chemically so extremely varied plant material provides the animal's 

 nutrition, and part of the food components furnish the requisite energy 

 as a result of the slow combustion during the so-called respiratory 

 process. These oxidizable substrates tend to belong primarily to the 

 groups of carbohydrates, fats, and proteins, quite familiar to us from 

 human dietetics. 



Now the scientist who, armed with this knowledge of the basis on 

 which rests the life of plants and animals, investigates the correspond- 

 ing situation in the world of the microbes, is apt to experience one 

 shock after another. It is true that occasionally he will encounter 

 some groups of micro-organisms whose metabolic features correspond 

 essentially to those of the green plants and animals, respectively, but 

 for the vast majority of microbial types that also multiply profusely 

 in the absence of light the conditions for animal metabolism appear 

 not to be realized in the least. A first surprise comes with the finding 

 that for many bacteria the organic foodstuff, and hence also the sub- 

 strate for respiration, may be limited to one single organic substance, 

 and that this may even be a member of some class far removed from 

 the groups of carbohydrates, fats, and proteins. 



Far more surprizing is, however, the fact that frequently any one of 

 a vast number of compounds, quite divergent in chemical respect, 

 can serve as the sole organic food constituent for one and the same 

 bacterial species. If one ponders the nature of such nutrient sub- 

 strates, the astonishment ever increases. For what should one think 

 of bacteria that apparently feel quite comfortable if they are provided 

 with carbon monoxide as the exclusive respiratory substrate, i.e., with 

 the substance, designated as 'coal gas', that has acquired such a bad 

 reputation in human society because its presence in very low concen- 

 tration in the air soon terminates all human and animal life? Still 

 more astounding is perhaps the demonstration that among the accept- 



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