420 



PRINCIPLES OF SOIL MICROBIOLOGY 



this may be due to the direct assimilation of the amino acids for the 

 synthesis of microbial protoplasm. 



In summarizing the energy utilization by different groups of micro- 

 organisms, it may be said that fungi transform usually 30 to 60 per 

 cent of the substrate into mycelium, aerobic bacteria 10 to 20 per cent, 

 while anaerobic bacteria may transform only 1 per cent or less of the 

 nutrients into synthesized cells. 



Reduction of nitrates and sulfates and energy utilization. In addi- 

 tion to respiration by the agency of free oxygen (autotrophic and 

 heterotrophic) and intramolecular respiration or "fermentation," 

 there is another form of respiration whereby the oxygen in certain 

 inorganic compounds, namely nitrates and sulfates, is utilized. Just 

 as the oxidation phenomena are accompanied by the liberation of 



TABLE 29 



Influence of temperature upon growth and energy utilization of Bad. vulgar e 



energy, so are the reduction phenomena accompanied by the consump- 

 tion of energy. This energy is, however, returned even to a greater 

 extent in the accompanying oxidation. The oxygen rich compounds 

 are reduced and the oxygen is utilized for the oxidation of other sub- 

 stances, the latter process supplying the energy for the former. 

 Nitrification, which is #n oxidation process, is accompanied by the 

 reduction of C0 2 , which is used as a source of carbon; denitrification, 

 which is a reduction process, is accompanied by oxidation phenomena 

 (oxidation of carbohydrates, etc.), in which the combined oxygen is 

 used to produce energy. 



The oxygen obtained from the nitrate or the sulfate is utilized for 

 the oxidation of carbohydrates, organic acids or certain inorganic 

 substances. This may be accomplished by one organism, as in the case 

 of the denitrifying sulfur-oxidizing organism, or by the symbiotic 



