ANAEROBES 



117 



At different levels of E^ it can well be imagined that different hydrogen donators 

 (AH2) and different hydrogen acceptors (B) come into use, and that these require 

 different enzymes ; so that the powers of bacteria to utilise such systems as sources 

 of energy and hence to multiply at different levels of E^ depend on the enzymic 

 activities which they are able to call into play. 



^^ 



o 

 



+ A 



+ 2 



O --2 -4 



Fig. 27 

 Reducing activities at different levels of E^ of hypothetical aerobe and anaerobe 



The anaerobes present in an acute form the difference between bacteria and 

 multicellular organisms. " Coarse" growing organisms, like Esch. coli, possess such 

 a wealth of varied enzyme systems that they are able to adapt themselves to a wide 

 variety of conditions, that is to say they are able to utilise many different substrates to 

 obtain energy, and one or other of their enzyme systems are able to function under 

 most cultural conditions. The anaerobes on the other hand probably have deficiencies 

 in their armoury. They are deficient in cytochromes and oxygen utiHsing systems so 

 they are unable to effect metabolic reactions and are unable to obtain the resulting 

 supplies of free energy for synthetic reactions at high oxidation-reduction potential 

 levels. This defect is cumulative ; not only are they unable to start processes under 

 oxidising conditions but they are unable as a result to start the synthetic and reductive 

 processes which would assist in providing the energy and raw materials for anaerobic 

 processes. When components of an enzyme reaction are kept permanently in an 

 oxidised condition things may be brought to a standstill for lack of activated radicals 

 which require to be partly reduced. 



In addition, the type of reation which anaerobes are able to effect probably 

 require SH activation and in the presence of air these may be all oxidised; 



In the terms of the Pasteur effect mentioned in the previous chapter, anaerobic 

 fermentations are inhibited by aerobic oxidation of various intermediates in the 

 glycol}i}ic chain, and since the anaerobe is deficient in the enzymes which can, in 

 parallel reactions, effect reductions, the anaerobic fermentations are permanently 

 stagnated. 



To summarise, therefore, the Clostridia are incapable of aerobic growth at a high 

 oxidation-reduction potential because they are deficient in enzymes capable of 

 utiHsing oxygen ; they are deficient in iron porphyrin enzyme systems such as catalase 

 and cytochrome. Not only does this prevent them obtaining energy by the oxidation 

 of nutrient material at the relating high oxidation-reduction potentials at which they 

 function but also oxygen is not passed on to other enzyme systems not containing iron 

 porphyrins, so that there may be a scarcity of acceptable hydrogen acceptors for 



