248 BACTERIOLOGICAL CHEMISTRY 



carboxyl group of pyruvic acid when Esch. coli acts on 

 pyruvic acid and " labelled " sodium bicarbonate, 

 NaHCi^Og. 



Some bacteria, such as Lactobacillus delbrilckii, 

 Neisseria gonorrhcece and Streptococcus hcemolyticus , con- 

 tain pyruvic oxidase which catalyses the conversion of 

 pyruvic acid to carbon dioxide and acetic acid : — 



CH3CO.COOH — > CO2 + CH3COOH. 

 Probably acetaldehyde is formed as an intermediate 

 step and its oxidation takes place with f la vine adenine 

 dinucleotide as co -enzyme or carrier ; the decarboxyla- 

 tion and oxidation are linked processes and do not occur 

 independently. Pyruvic oxidase is inhibited by cyanide 

 or fluoride, but yeast carboxylase is not. 



The anaerobic dismutation of pyruvic acid to lactic 

 and acetic acids and carbon dioxide probably also involves 

 pyruvic oxidase and a carrier : — 



CH3CO.COOH H2 CH3CHOH.COOH 



+ +11 — > + 



CH3CO.COOH CH3COOH + CO2 



Esch. coli yields a certain amount of ethyl alcohol 

 during fermentation as well as the main acid products. 

 It is thought that the alcohol arises as the result of a 

 dismutation (the term applied to the enzymatic equivalent 

 of the Cannizzaro reaction) of acetaldehyde : — 



CH3CHO CH3COOH (acetic acid) 





 + + II > + 



Ha 

 CH3CHO CH3.CH2OH (ethyl alcohol) 



Before the end of the nineteenth century it was shown 

 by Hoppe-Seyler that the gas production by bacteria was 

 almost certainly due to the breakdown of formic acid or 

 of formates. He showed that organisms producing gas 

 from glucose all fermented formates, whilst those which 

 were not gas producers did not ferment formates. Harden 

 showed that Esch. coli and Eberth. typhosa when grown 

 anaerobically on glucose broke down half the sugar to 



