MICROBIAL METABOLISM AND ITS INDUSTRIAL IMPLICATIONS 



portance, since it means that in both respiration and fermentation the 

 reaction 



AH 2 +B -> A+BH 2 



plays an essential role, and that the difference between the two is 

 restricted to the fact that in fermentation the molecule B is organic 

 and derived from the substrate itself, whilst in respiration the molecule 

 which ultimately acts as B is free oxygen. 



This throws a clear light on a series of dissimilatory processes which 

 for a long time have occupied a separate position in microbiology. I 

 refer to the processes of nitrate and sulphate reduction, and the proc- 

 ess to which I have earlier referred as methane fermentation. For - as 

 indicated in Table VII - there is now every reason to consider these 

 processes as reactions in which nitrate, sulphate and carbonate act 

 as the final hydrogen acceptor B of the general equation given, and in 

 doing so can be reduced to the ultimate hydrogenation stages of nitro- 

 gen, sulphur and carbon, which elements thus share the fate of oxygen 

 in respiration. 



TABLE VII 



The principle of transhydrogenation as the essence of dissimilation 

 processes 



AH 2 +B-^ A+BH, 



Fermentation : 



AH 2 -B-> A+BH 2 

 Respiration: 



AH 2 +V 2 2 -> A+OH 2 

 Nitrate reduction : 



4 AH 2 +HN0 3 -^ 4A+NH 3 +3H 2 

 Sulphate reduction : 



4AH 2 +H 2 S0 4 -> 4A+SH 2 + 4 H 2 

 Carbonate reduction: 



4AH 2 +H 2 C0 3 -^ 4A+CH 4 +3H 2 



This is another very impressive aspect of the great adaptability of 

 microbial life to potential sources of chemical energy and one is in- 

 clined to see this as the result of an evolutionary trend. For germs 



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