76 BACTERIAL METABOLISM 



(c) Betaimidazoleethylamine from histidine. 



H C NH V H C NH V 



\r*t \r | fi 



II //^- II //^* 



C N * = C N * + CO 2 



I I 



CH 2 CH 2 



I I 



CHNH 2 CH 2 NH 2 



I 

 COOH 



Histidine. Betaimidazoleethylamine. 



According to Vaughan, 1 betaimidazoleethylamine is possibly the 

 active poisonous principle of the protein molecule. Recent investiga- 

 tions would suggest that its liberation in the intestinal tract as the 

 result of bacterial decomposition of protein there and its absorption 

 into the body may be associated with symptoms of considerable 

 severity. The substance is not formed as a product of bacterial 

 metabolism in media containing utilizable carbohydrates. 



B. Reactions of Bacteria in Media Containing Both Utilizable 

 Nitrogenous Substances (Protein and Their Derivatives) and Carbo- 

 hydrates. Carbohydrates contain no nitrogen; consequently pure 

 carbohydrate solutions are not complete foods for bacteria, they 

 are important chiefly as sources of energy to them. Generally speak- 

 ing, carbohydrates containing two, four, five, seven or eight carbon 

 atoms are not readily fermentable by bacteria. Those containing 

 six carbon atoms, particularly dextrose, are most readily utilizable, 

 those with three carbon atoms, generally speaking, somewhat less 

 so. Bioses, containing twelve carbon atoms, and starches appear to 

 be hydrolyzed to sugars containing six carbon atoms before they are 

 finally oxidized. 



The final utilization of sugars for energy by bacteria varies accord- 

 ing to the type of organism; the following qualitative reactions are 

 illustrative of some of the general types of decomposition usually met 

 with. It must be remembered that the exact quantitative utilization 

 of carbohydrates by bacteria and the nature and composition of many 

 of the intermediary products formed from them are still uncertain. 



1. C 12 H 22 On + H 2 O = C 6 H 12 O 6 + C 6 H 12 O 6 . 



Lactose. Dextrose. Galactose. 



Hydrolytic cleavage of a biose to two molecules of hexose sugar. 



2. C 6 Hi 2 O 6 = 3CH 3 COOH. Pure acetic acid fermentation. 



3. C 6 H 12 O 6 = 2CH 3 CHOHCOOH. Pure lactic acid fermentation. 



1 Protein Split Products. 



