METHANE FORMATION 155 



The organism \vill not attack methyl alcohol but will grow on 



ethyl alcohol, when the rate of growth bears a linear relation 



to the acetic acid production, and the greater part of the 



carbon of the organism is derived from the acetate so formed. 



Proof that methane arises from carbon dioxide was obtained 



by carrying out the oxidation of alcohol in the presence of 



carbon dioxide enriched with isotopic-C, when it was found 



that the carbon dioxide was converted to methane and the 



bulk of the isotopic-carbon appeared in the methane produced, 



although small amounts were assimilated by the organism. 



The strictly anaerobic Clostridia obtain their energy in 



many cases by oxido-reduction reactions. In some cases 



the hydrogen donator and acceptor are both amino-acids, 



so that a reaction occurs in which one amino-acid is oxidised 



to the corresponding keto-acid, while the other is reduced 



to the corresponding fatty acid, both amino-acids becoming 



deaminated : 



R X R X 



I III 



CHNH2 + H2O + CHNH3— ^ CO + 2NH3 + CHo 



I I I I " 



COOH COOH COOH COOH 



This reaction is called the Stickland reaction and is discussed 

 in further detail in Chap. IX. 



Alcohol is a hydrogen donator in the case of CI. kluyverii 

 studied by Barker and his co-workers (pp. 145-7). This organism 

 cannot attack glucose or pyruvic acid but obtains its energy by 

 the metabolism of ethanol and acetate. The growth requires 

 CO2, and isotopic studies have shown that the amount of CO2 

 assimilated is proportional to the amount of acetate meta- 

 bolised, but that 70 per cent, of the carbon of the CO2 appears 

 in the cellular material and none in the other products. The 

 main products of the metabolism of the ethanol and acetate are 

 butyric and caproic acids, but gaseous hydrogen is also formed 

 and this arises from oxidation of ethanol : 



CH3CH2OH + HgO-^CHg.COOH + 2H2. 



