CHAPTER VII 



THE NUTRITION OF THE HETEROTROPHIC 

 BACTERIA 



WHEN bacteria grow and reproduce there occurs a 

 synthesis of all the many cell constituents, the 

 proteins and nucleoproteins of the protoplasm, 

 polysaccharides, fats, phosphatides and a number of 

 other carbon compounds. The elements, mainly carbon, 

 nitrogen, hydrogen and oxygen, but also phosphorus, 

 sulphur and certain metals in smaller amount, required 

 for these syntheses have to be supplied in an available 

 form by the medium in which the organism is grown. 



As would be expected from an analysis of the ash 

 of bacteria, the inorganic constituents which must be 

 supplied are mainly phosphorus, sulphur, sodium, potas- 

 sium, magnesium, calcium, iron and chlorine. It is 

 probable that the metals needed in only small amount 

 form part of enzyme systems. Iron is an essential part 

 of the cytochrome complex ; phosphorus, potassium and 

 magnesium are also intimately involved in respiratory 

 mechanisms (see Chapter XII). Corynebacterium diph- 

 therioe, Clostridium tetani and CI. welchii need small 

 amounts of iron in order to produce their toxins. 



We have seen that the autotrophic bacteria derive 

 their carbon from carbon dioxide and their nitrogen from 

 ammonia, nitrites or nitrates ; accordingly, they must 

 possess a very complete equipment of the enzymes 

 necessary to carry on these syntheses from such simple 

 starting materials. It seems probable that the hetero- 

 trophic bacteria, which, in general, require much more 

 complicated sources of carbon and nitrogen, have lost some 



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