12 MICROORGANISMS IN SOILS AND WATER BASINS 



NUTRITION OF MICROORGANISMS IN 

 NATURAL SUBSTRATES 



It was at first assumed that bacteria and other microorganisms possess 

 a simpler type of metabolism than do higher plants and animals j al- 

 though some can obtain all the nutrients required for cell synthesis and 

 energy from simple elements and compounds, others need for their nu- 

 trition certain highly complicated organic substances. Recently it has 

 been recognized that various "growth-promoting" substances or vita- 

 mins play an important role in the nutrition of many microorganisms. It 

 has also been established that highly complicated enzyme systems are 

 produced by these lower forms of life, and that many interrelationships 

 exist among their metabolic processes, the composition of the medium, 

 and the environmental conditions. One thus begins to realize that the 

 metabolism of these microbes is also highly complicated. Most of the in- 

 formation on their nutrition is based upon their growth on artificial cul- 

 ture media. In nature, however, these organisms live in associations and 

 vary considerably in the degree of their interdependence. As yet no 

 laboratory method has been developed that duplicates these conditions. 



Microorganisms vary considerably in their nutrition and energy 

 utilization, as well as in the breakdown and transformation of the avail- 

 able nutrients. Certain elements or compounds are required for cell 

 synthesis. In some cases, certain trace elements as well as varying con- 

 centrations of growth-promoting substances are also essential. Among 

 the nutrient elements, nitrogen occupies a prominent place. Consider- 

 able variation exists in the ability of microorganisms to utilize different 

 types of nitrogen compounds: some can obtain their nitrogen from a 

 wide variety of substances; others are restricted to the use of a single 

 group of compounds such as proteins, amino acids, urea, ammonia, or 

 nitrate; a few are able to use atmospheric nitrogen. The variety of or- 

 ganic nitrogenous bodies supplied to microorganisms in soils and in 

 water basins is limited only by the number of such compounds synthe- 

 sized by plants and animals. The complex forms of nitrogen are broken 

 down to simpler compounds; these may be assimilated by organisms 

 and again built up into complex forms, or they may be utilized only by 

 other organisms. Microbial activity thus regulates the state of the nitro- 



