MICROBIAL METABOLISM AND ITS INDUSTRIAL IMPLICATIONS 



parently puzzling situation has been unravelled to the extent that it 

 has become clear that we are dealing with mixed fermentations, or in 

 other words that one part of the substrate molecule undergoes a con- 

 version which differs from that to which a second part is subjected. 

 This obviously explains both the absence of stoichiometrical relation- 

 ships and the dependence of the results on external conditions. We 

 must, therefore, conclude that bacterial fermentations as a rule com- 

 prise a number of elementary processes; some of the more important 

 elementary processes occurring in sugar fermentations have been col- 

 lected in Table IV. 



TABLE IV 



Various types of fermentative glucose dissimilation by micro-organisms 

 Elementary processes 



C 6 H 12 O e -> 2CH 3 CH 2 OH+2C0 2 



ethyl alcohol 



C ft H 19 R -> 2CH, • CHOH • COOH 



J 6 AX 12 W 6 



acid 



i 1 / 2 C 6 H 12 6 ->2CH3-CH 2 -COOH+CH 3 -COOH+C0 2 +H 2 



propionic acid acetic acid 



C 6 H 12 6 -> CH 3 • CHOH • CHOH • CH 3 + 2 C0 2 +H 2 



2,3-butanediol 



3C 6 H 12 6 -> 2CH 3 • CHOH • CHOH • CH 3 +2CH 2 OH • CHOH • CH 2 OH 



2,3-butanediol glycerol +4.C0 2 



C 6 H 12 6 ^ CH 3 • CH 2 • CH 2 • COOH+ 2 C0 2 + 2H 2 



butvric acid 



7. C 6 H 12 6 + 4 CH 3 CO-CH 3 + 3 C0 2 + 4 H 2 



8. C 6 H 12 6 -> 3CH 3 ■ COOH 



acetic acid 



N.B. Most bacterial fermentations comprise two or more elementary processes. 



The separate elementary fermentation processes also present diffi- 

 cult riddles to the chemical mind. The only clear fact is that they show 

 a common characteristic, viz., that certain of the compounds formed 

 are in a reduced state as compared with the substrate, whilst other 

 compounds are oxidized. This is nowhere better shown than in the so- 

 called methane fermentation. Bus well has shown that his crude cul- 

 tures of methane bacteria succeeded in converting the most diverse 



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