THE CHEMICAL CHANGES PRODUCED BY BACTERIA 53 



(see Werkman 1939) and from Bad. coli by Endo (1938) ; moreover, it is formed during 

 the breakdown of hexose diphosphate. 



The difficulty of obtaining active cell -free extracts of bacteria similar to those of the 

 nmch more extensively studied yeasts has been overcome by disintegrating bacteria by 

 ultra-sonic vibrations (see Chapter 5) or in special crushing mills (Booth and Green 1938). 

 By the latter means, for example. Still (1940) has demonstrated that cell-free preparations 

 of Bad. coli wiU catalyse the oxidation of triosephosphate (3-phosphoglyceraldehyde) to 

 3-phosphoglyceric acid. 



It must be emphasized that this is one example only of the possible ways of 

 anaerobic glycolysis. Indeed, it is probable that two or more processes of glyco- 

 lysis, only one of them involving phosphorylation, may occur at the same time 

 in a bacterial culture (see Tasman and Brandwijk 1938). The applicabihty of 

 the Embden-Meyerhof-Parnas scheme to bacteria is by no means fully established, 

 but it serves to illustrate not only the complexity of the mechanisms, but their 

 dependence, in certain cases at any rate, on a number of enzymes and carriers, 

 which themselves may be intermediaries between stages on other metaboUc paths. 



Among the intermediate products of the carbohydrate metabolism of bacteria, pyruvic 

 acid holds an important place, whether the metabolic path actually followed corresponds 

 to the Embden-Meyerhof-Parnas scheme or to one of the alternative schemes that have 

 been proposed. It is a source of acetic, succinic, butyi'ic and fumaric acids, of ethyl 

 and iso-propyl alcohol, acetone, glycerol, acetylmethylcarbinol, butylene glycol, carbon 

 dioxide and hydrogen. Werkman (1939) lists the following examples of anaerobic dis- 

 similation of pyruvic acid produced by bacteria and yeasts. 



1. Decarboxylation, giving acetaldehyde and COg {Sarcina veniriculi, Smit 1930). 



CH3COCOOH -^ CH3CHO + CO2. 



2. Hydrolysis, giving acetic and formic acids {Baderiacece, Tikka 1937). 



CH3COCOOH + HOH -> CH3COOH + HCOOH. 



3. Dismutation of the acetaldehyde produced by decarboxylation, giving acetic acid 

 and alcohol (?many acetic acid bacteria.) 



2CH3CHO -> CH3COOH ; C2H5OH. 



4. Condensation of the acetaldehyde to produce acetylmethylcarbinol, and reduction, 

 giving butylene glycol {Bad. aerogenes, Neuberg and Reinfurth 1923-24). 



2CH3CHO —> CH3COCHOHCH3. 

 CH3COCHOHCH3 + 2H — J- CHg-CHOHCHOHCHa. 



5. Dismutation and reduction, giving acetic and lactic acids, and COj (lactic acid 

 bacteria. Nelson and Werkman 1936, Staph, aureus, Krebs, 1937). 



CH3COCOOH + HOH -^ CH3COOH + 2H + CO2. 

 CH3COCOOH + 2H ^- CH3CHOHCOOH. 



The metabolism of pyruvic acid is closely connected with thiamin (vitamin B^). The 

 co-enzyme necessary for reaction 1, a cocarboxylase, has been identified as the diphosphate 

 of thiamin and is necessary for the breakdown of pyruvic acid by Bad. acidificans longis- 

 simum (Lipmann 1937), Staph, aureus (Hills 1938), propionic acid bacteria (Silverman 

 and Werkman 1939), and Str. hcBmolyticus and gonococci (Barron and Lyman 1939). 



As noted above (p. 45), for the purposes of classification of bacteria the power of 

 a species to break down a given carbohydrate is usually measured by the production of 

 acid or of acid and gas. The gases produced in macroscopic quantities from small volumes 

 of fluid medium are usually COj and Hj. We have noted a number of ways in which 

 hexose sugars may be supjjosed to give rise to various acids and COg. Pakes and JoUy- 

 man (1901) tested certain members of the Baderium group and showed that all those 



