138 PROVISION OF energy: fermentation 



Some strains of Aerobacter can effect a reduction of acetyl- 

 methylcarbinol to 2.3.butylene glycol: 



CH3.CO.CHOH.CH3+2H^— CH3.CHOH.CHOH.CH3 (10) 



This fermentation product is of considerable commercial 

 interest as it is a comparatively simple matter to convert it 

 by chemical means to butadiene, CH2=CH — CH^CHg, 

 which is one of the materials used to produce synthetic rubber 

 by polymerisation. Acetylmethylcarbinol also undergoes 

 oxidation by oxygen to diacetyl CH3.CO.CO.CH3, which is 

 the substance imparting the "buttery" smell to butter. 



Acetylmethylcarbinol is produced by species of Pseudomonas 

 and Bacillus as well as by Aerobacter. 



THE FERMENTATION OF PYRUVIC ACID BY 

 PR OPIONI BACTERIA 



Certain bacteria found in Gruyere and Emmentaler cheeses 

 produce propionic acid amongst their fermentation products. 

 These Propionibacteria ferment pyruvic acid to form propionic 

 acid, and since they also reduce lactic acid to this same 

 product, it has been suggested in the past that lactic acid 

 forms an intermediate stage in the reduction of pyruvic acid 

 to propionic acid. However, Barker and Lipmann have 

 found that the decomposition of lactate is inhibited by sodium 

 fluoride at a concentration considerably less than that required 

 to prevent the formation of propionic acid from pyruvic acid. 

 This indicates that lactic acid cannot act as an intermediate 

 in the latter reaction, but that the following scheme is involved. 



2H 2H 

 CH3.CO.COOH > X > CH3.CH2.COOH 



\x t 



^ I NaF 



^CH^.CHOH.COOH 



where the nature of X is unknown. 



The Propionibacteria form succinic acid from pyruvic acid 

 by the fixation of carbon dioxide in the same way as that 



