BACTERIAL PEROXIDE 



109 



somewhat after the logarithmic phase of growth but does not reach the high levels 

 reached with streptococci and which correspond to peroxide formation. 



If, now, two further organisms are studied, namely, pneumococcus and staphy- 

 lococcus, it is found that the pneumococcus (fig. 13) behaves like hsemolytic strepto- 

 coccus, whilst the staphylococcus (Hewitt, 1930, 3) resembles C. divhthericB. It 

 is significant that streptococci and pneumococci can form peroxide in cultures 

 whilst C. diphthericB and staphylococci do not. 



o 



S3 



20 40 



100 120 140 



Time (hours) 



Fig. 21 



Peptone infusion broth cultures of C. diphtherice 



This brings us to an important phase in bacterial respiration and one which may 

 be particularly amenable to study by electrode potential measurements. 



BACTERIAL PEROXIDE AND CLASSIFICATION OF ORGANISMS 



Hydrogen peroxide is of much more frequent occurrence than has perhaps been 

 generally realised. The occurrence of hydrogen peroxide is supposed necessarily 

 to accompany the formation of activated hydrogen in the presence of molecular 

 oxygen. Much evidence has accumulated to prove the existence of dehydrogenating 

 enzymes in bacteria. These activate the hydrogen in a hydrogen donator so that it 

 is transferred to a hydrogen acceptor. Thus, in the presence of B. coli two atoms of 

 hydrogen may be transferre(] from lactic acid to fumaric acid, whereby the lactic acid 

 is oxidised to pyruvic acid and the fumaric acid is reduced to succinic acid ; thus : — 



CH3CHOH.COOH + COOH.CH : CH.COOH -> CH3.CO.COOH + (COOH.CHa)^ 

 lactic acid fumaric acid pyruvic acid succinic acid 



Oxygen itself may play the role of hydrogen acceptor and hydrogen peroxide 

 is formed. Thus, in the presence of xanthine oxidase, xanthine is oxidised in the 

 air to uric acid with concomitant formation of hydrogen peroxide : — 



Xanthine + O2 -> uric acid + HgOa- 



The evidence for peroxide formation (Thurlow, 1925) frequently depends on such 

 reactions as the oxidation of nitrate bv the reaction mixture when peroxidase is added. 



