CHAPTER VI 



BACTERIOLOGICAL APPLICATIONS 



Why do bacterial cultures often develop strongly reducing conditions during 

 growth ? The answer is not perhaps obvious at once, but, as will be seen later, 

 reduction follows as a necessary result of the metabolism of the organisms. In order 

 to understand the origin of the electrode potentials developed it is necessary to consider 

 briefly the nature of the metabolic processes occurring in bacterial cultures and also 

 how these diifer from the metaboUc systems of highly organised multicellular 

 organisms. 



LAG PHASE 



When bacteria are subcultured into fresh media there is usually a lag phase 

 before the number of bacteria present begins to multiply appreciably. It is imtriguing 

 to speculate why normal multiplication does not start immediately. It is evident 

 that the spores of spore-bearing bacteria will require time to " germinate " before 

 normal multiplication gets into its stride, but it is not so obvious that non-sporulating 

 organisms should, when freshly subcultured and presented with abundant fresh food, 

 undergo a phase lasting sometimes several hours before they begin to multiply at an 

 appreciable rate. It is found that in this initial non-multiplying phase bacteria are 

 generally increasing in size. Thus Wilson (1926) found the average size oi Salmonella 

 typhimurium cells to be 2-35 x 0-79 after 4 hours incubation and 1-13 X 0-49 after 

 26 hours. The volume of the lag phase cells is therefore more than five times that of 

 their successors. The metabolic activities of the bacteria are intense during the lag 

 phase (Winslow and Walker, 1939) and the oxidation-reduction potential of the 

 culture is falling, as is seen in curves given later in this chapter. 



At this stage it is necessary to draw attention to a concept that will be returned 

 to more than once and that is the great difference between the life-problems of 

 unicellular bacteria immersed in a foreign medium and the cells of multicellular 

 higher organisms with their carefully adjusted environment with " everything laid 

 on." The difference suggests that between an explorer setting up his bivouac and a 

 town dweller returning to his service flat. Modern work of the last two decades has 

 brought out with remarkable success the similarities and identities of bacteriological 

 and "physiological " processes, but it appears necessary to emphasise that enthusiasm 

 for recognising the analogies should not blind us to the differences. 



The cell of a higher animal generally is highly specialised and is presented with 

 nutriment exactly adjusted to his needs ; the unicellular bacterium is faced with 

 great difiiculties and many things seem badly adjusted for him when he is freshly 

 subcultured. Glucose may be available in quantity and also oxygen, but many stages 

 must be gone through before 



CeHi^Oe + 6 O2 -> 6CO2 -f 6H2O 



The delicately adjusted aerobic and anaerobic glycolysis systems require many 

 enzymes and coenzymes to function in tune under carefully controlled conditions. 

 Glucose and oxygen are at the opposite ends of the metabolic chain. The initial 

 stages of glycolysis tend to be anaerobic and oxygen is required in the later stages. 



