96 OXIDATION-REDUCTION POTENTIALS 



As would be expected the lag in multiplication of bacteria newly subcultured is 

 longer if the inoculum consists of an old culture in which the cells have spent a long 

 time since multiplying, are therefore themselves " senile," and the enzymes, 

 themselves proteins, are likely to be partly denatured with labile prosthetic groups 

 decomposed . In this connection it should also be mentioned that many bacteria possess 

 a variety of proteolytic enzymes and under some conditions are subject to complete 

 autolysis. It requires little imagination to visuahse self-destruction of enzymes with 

 age. 



Hinshelwood (1948) in a stimulating discussion emphasises the possibility of 

 intermediate metabolites diffusing from the cells so that enzymic systems will not 

 have the necessary substrates preformed for their activities. 



Another point that will be developed later is the conditions in which the newly 

 subcultured bacterial cells find themselves. Their breakdown of carbohydrates 

 follows a plan roughly similar to that of the metabolic chains of glycolysis and 

 fermentation developed in the previous chapter. In these the glycolytic system starts 

 with the " reduced type " of reaction and ends up with the " oxidised type," and 

 finally oxygen gas itself enters the system through the intermediation of haemoglobin, 

 cytochrome, etc. The bacterial cell on the other hand is faced with the problem of 

 starting the metaboHc chain involving reduced reactants with conditions that are 

 oxidising. The Pasteur effect is relevant here ; the presence of oxidising conditions 

 inhibits fermentation activities. The bacterial cell, unlike the animal tissue cell has 

 to alter its environment before it can get into normal action. 



Finally the question of bacterial enzyme adaptation occurs ; the old cells 

 presumably have their enzyme systems adapted to dealing with conditions as they 

 are in an old partially exhausted culture medium and the sequential development of 

 enzymes now has to be begun for the utihsation of the substrates as they occur in a 

 fresh culture medium. This again differentiates bacteria from tissue cells — not only 

 do the bacteria have to adapt their own environment (they have no organised central 

 authority to work in concert with them for the delivery of supplies at the right time, 

 and concentration and no maintenance department for the engineering services), but 

 they have to adapt themselves to changing environment so that bacteria in cultures 

 of different ages have to have differently adjusted enzyme systems. This will be 

 discussed in greater detail later. 



There is also the possibility of stale cells producing poisons and inhibitors against 

 their own enzyme systems, but there is no evidence that diphtheria toxin, for instance, 

 will poison the cells that produced it. 



The lag in initiation of growth shown by aged cells of B. coli in a medium con- 

 taining ammonia as sole nitrogen source has been traced to the need for the production 

 from glucose of four-carbon compounds which can be aminated to yield essential 

 amino-acids. The lag almost vanishes when glutamic acid or a-ketoglutaric acid 

 is added (Morrison and Hinshelwood, 1949). 



LOGARITHMIC GROWTH PHASE 



Having surmounted its initial difficulties of adaptation to the fresh environment 

 the bacterial cell now enters the active multiplication stage. The reproduction rate is 

 now very high, the reproduction time may be as short as 20 minutes. That is to say 



