CHAPTER VII 



PKOVISION OF ENEKGY: FERMENTATION 



In the last chapter we considered the materials which are 

 essential for the growth of various bacterial species. The 

 growth process involves assimilation of these materials and 

 their elaboration into the constituents of the living cell. These 

 cellular constituents are often far more complex than the 

 nutrient materials; for example, the autotrophic bacteria 

 synthesise protein molecules from ammonia and carbon 

 dioxide. In other words, the energy content of the cell 

 constituents is higher than that of the raw materials and, con- 

 sequently, energy has to be suppHed before cell synthesis and 

 growth can occur. The gain in energy of the cell constituents 

 is obtained by degradation of other energy-rich materials in 

 the environment. The bacterial cell often obtains its energy 

 by the degradation of carbohydrates in the environment, and 

 this degradation can be accompUshed anaerobically, in which 

 case the process is called " fermentation," or aerobically by 

 oxidation processes. In this chapter we shall consider the 

 fermentation process. 



The products of bacterial fermentation are many and varied, 

 and it has been shown in Chap. II that bacteria can often be 

 '^: separated and differentiated on the basis of their fermentation 

 reactions considered with respect to the sugars fermented and 

 the products formed from those sugars. It is undesirable to 

 deal here with the whole range of bacterial fermentations and, 

 indeed, many have not yet been worked out in detail. In 

 some cases bacterial fermentation provides an easily controlled 

 method for the production of a commercially valuable sub- 

 stance such as butyl alcohol, and in others the production of 

 an easily identified and specific product can be used as a 

 characterisation test. In these cases detailed investigations 

 have been carried out with the intention of elucidating the 

 metabolism involved. The problem is also of interest to the 

 biochemist interested in carbohydrate metabolism, and the 

 fermentation of Esch. coli and Aerobacter aerogenes has received 



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