CHAPTER VIII 



PROVISION OF ENERGY: OXIDATION 



In the last chapter we dealt in detail with the anaerobic 

 decomposition of carbohydrates. In this chapter we shall 

 proceed to study the liberation of energy by oxidative pro- 

 cesses. As explained in Chap. Ill, oxidation does not 

 necessarily involve molecular oxygen since any substance 

 AHg can be oxidised by the general oxido-reduction reaction : 



AH2 + B ^ A + BH2. 



Oxygen can take the place of the hydrogen-acceptor B. 

 Oxidation reactions thus do not depend upon the presence of 

 atmospheric oxygen and can be carried out by anaerobic as 

 well as aerobic organisms. However, where the organism is 

 living an aerobic existence and a substrate AHg can be oxidised 

 directly, or indirectly through a chain of reactions, by oxygen, 

 the accumulation of reduced products is avoided and the 

 provision of energy by such complete oxidation is obviously 

 greater than by a fermentation process. Consequently a 

 facultative anaerobe grows more efficiently in air than 

 anaerobically. 



The oxidation of carbon substances is too wide and complex 

 a subject to deal with in detail here, and we shall restrict the 

 discussion to the mechanisms employed by typical examples of 

 aerobic, facultatively anaerobic, and anaerobic bacteria to 

 carry out key oxidations centring on alcohol as substrate. 



OXIDATIONS IN ACETOBAGTER 



The commercial production of acetic acid as vinegar has 

 been based for many years on the power of certain strictly 

 aerobic- bacteria, Acetohacter, to oxidise ethyl alcohol. The 

 process has been commonly called " acetic fermentation," 



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