METABOLISM OF MICROORGANISMS 



383 



or, more probably, a decarboxylation product of succinic acid. The latter 

 may be formed by uptake of carbon dioxide with pyruvic to form oxal- 

 acetic acid, and subsequent reduction of this to succinic acid. 



CO2 + CH3-C0-C00H > HOOC-CH.CO-COOH > 



HOOC-CHo-CH,COOH + H2O 



The uptake of carbon dioxide by propionic acid bacteria was first demon- 

 strated by AVood and Werkman, and tliis mechanism is therefore desig- 

 nated as the Wood- Werkman reaction. 



Succinic acid is also assumed to be formed by oxidative condensation 

 of two molecules of acetic acid. The overall equation is 



HOOC CH3 + CH3COOH -^ HOOC CHoCHoCOOH + 2H 



The two hydrogens are not released as gas but are used for the reduction of 

 other compounds. 



Acetoin (acetylmethylcarbinol) is formed in both yeast and bacterial 

 fermentations. In yeast it is formed by condensation of pyruvic acid 

 and acetaldehyde, and in bacteria by condensation of two moles of 

 pyruvic acid. a-Acetolactic acid is an intermediate in each case. Equa- 

 tions for the formation by yeast may be expressed as follows: 



CH3CO • COOH + CH3CHO -> CHo • COH • COOH 



I- 



CO • CH3 

 CH3CO • COH • CH3 -^ CH3 • CO • CHOH • CH3 + COo 



COOH 



In the biosynthesis by bacteria the first equation involves both con- 

 densation and decarboxylation. 



2CH3CO • COOH -> CH3 • COH • COOH + CO. 



CO • CH3 



In the aerogenes fermentation, acetoin is reduced to give a major 

 product, 2,3-butylene glycol. 



CH3 • CO • CHOH • CH3 -f 2H -» CH3 • CHOH • CHOH • CH3 



In the colon-aerogenes fermentation, formic acid and hydrogen are 

 conspicuous products. These come from the hydrolytic cleavage of 

 pyruvic acid 



CH3CO • COOH + HoO^ CH3COOH + HCOOH 



and subsequent breakdown of formic acid by the enzyme, hydrogenlyase. 



HCOOH -> H., + CO., 



