556 



M. ISHIMOTO AND F. EGAMI 



potential consideration, they, especially sulphate-reducing systems, resemble 

 systems for fermentation, i.e. oxidation of organic substances by organic sub- 

 stances. These characteristics were also reflected in pecuharly ünkcd donor 

 systems. 



Table i 



Free-energy changes in various reductions 



In the presence of nitrate, Escherichia coli grows anaerobically on media con- 

 taining succinate or lactate as a sole carbon source. However, without nitrate 

 it does not grow in the same conditions [3]. In this case, nitrate substitutes for 

 oxygen. 



The products of fermentation by resting cells of E. coli are changed greatiy 

 by the addition of nitrate. According to Verhoeven [4], added nitrate caused 

 decrease in the amount of ethanol, lactate and succinate and a remarkable in- 

 crease of carbon dioxide (Table 2). These results clearly indicate stimulation 

 by nitrate of more complete oxidation of substrates, and resemblance of the 

 nitrate reduction to respiration. 



Table 2 



Products of nitrate reduction by glucose in E. coli. {Percentage of C calculated on 

 carbon content of glucose consumed in fermentation.) 



The sulphate reduction as an energy-yielding reaction is quite confined to 

 special organisms, sulphate reducers Dcsulfovibrio They are strict anaerobes and 

 their growth depends on the oxidation of lactate with sulphate in many cases; 



