294 BACTERIAL VARIATION 



insufficient ; it must be utilized by the metabolizing cell. Thus, the production 

 of the enzyme hydrolysing the specific polysaccharide of Type III pneumococcus 

 by Dubos and Avery's (1931) bacillus was retarded when nutrients more readily 

 assimilable than the polysaccharide were added to the culture (see also Dubos 

 1940). 



It should be noted that the appearance of an enzyme does not necessarily imply its 

 increased production ; the effect may be due to activation of an enzyme aheady existing 

 in considerable quantity. It may also be due to the removal of an inhibitor, rather than 

 the addition of a substrate. For instance, the tryptophanase system of Bad. coli is 

 adajjtive, but when tryptophan is present, glucose and phenylalanine wiU inhibit the 

 production of the enzyme system by resting bacteria (Evans, Handley and Happold 1940). 

 Dawson and Happold (1943) suggest that the phenylalanine may act by competing with 

 tryptophan for a labile component common to two enzyme systems, one the tryptoi:)hanase, 

 the other concerned with carbohydrate storage in the cell. 



Kocholaty and his colleagues (Kocholaty and Hoogerheide 1938, Kocholaty and 

 Weil 1938) report enzyme adaptations to variations in pH. They produced a shift in 

 the pH optima of, for example, the alanine and pyruvic dehydrogenases of CI. sporogenes 

 by varying the pH of the culture media ; and found that CI. histolyticum grown in a 

 casein medium produced proteinases with an optimum activity at pH 7-0, but when 

 grown in a casein -glucose medium at a lower pH, produced proteinases with an optimum 

 at pH 60. Cells from glucose -casein cultures, when transplanted to the plain casein 

 medium within 20 hours, had produced the proteinase with an optimum at pH 7 0. They 

 were also able to train CI. histolyticum to attack casein or gelatin alone, though normally 

 it attacks both equally well. This specificity was very labile, however, for when amino- 

 acids not present in the homologous protein were added to the medium the resulting 

 enzymes attacked both proteins. To explain these phenomena, they sought to combine 

 Yudkin's mass action theory with Quastel's theory of enzymes as metabolites by assuming 

 that relatively few colloidal carriers are available for a number of enzymes, and that 

 under different conditions these combine with different active groupings to form enzymes 

 of different activity or specificity. On this basis Yudkin's precursor may be a colloidal 

 carrier in equilibrium with various prosthetic groups of enzymes. On the other hand, 

 this type of pH adaptation may depend on a multiplicity of enzymes, van Heyningen 

 (1940), for example, described two proteinases in CI. histolyticum, one activated by cysteine, 

 appearing in the first 12 hours of growth, one appearing later which was inhibited by 

 cysteine. 



In other organisms, a close relation is demonstrable between the pH optima 

 of enzymes and the cultural conditions in which the enzymes come into play. 

 Thus, Bad. coli, Str. fcBcalis and certain Clostridia produce amines from amino- 

 acids by specific decarboxylases that act only between the limits pH 2-5 and 5-5. 

 These decarboxylases are formed only when the organisms are grown in acid 

 media (Gale 1940, 1941). Again, at a pH in the vicinity of 5-0, Bad. aerogenes 

 decomposes pyruvic acid with the formation of acetylmethylcarbinol ; at a 

 higher pH, this activity is entirely suppressed, and decomposition proceeds by 

 breakdown into acetic and formic acids (Silverman and Werkman 1941). Extend- 

 ing these investigations, Gale and Epps (1942) showed that Bad. coli could grow 

 in a casein digest at any pH between 4-5 and 9-0 and that, though with changing 

 growth pH, the enzymic constitution of the bacteria changed, there was no evidence 

 of any shift in the pH optima of individual enzymes. The enzymes concerned 

 fell into two groups. The formation of those in the first group increased as the 

 growth pH deviated from the pH at which their action was maximum, so that 

 in each cell the drop in activity due to the pH change was compensated by the 



