CHAPTER V 



GROWTH: SYNTHESIS OF BACTERIAL PROTOPLASM 



When a bacterium is inoculated into a nutrient medium 

 it first begins to increase in size, and this increase in cell- 

 material is eventually followed by binary fission, the two 

 daughter-cells proceeding to increase in size until they divide, 

 and so on. The speed at which this process takes place 

 depends upon the particular organism concerned and on the 

 physico-chemical constitution of the environment. Esch. coli 

 will divide once every twenty minutes when inoculated into a 

 nutrient broth at ^H 7 and 37° C. This means that each cell 

 synthesises its own weight of protoplasm including proteins, 

 enzymes, prosthetic groups, essential metabolites, etc., in 

 twenty minutes. In this chapter we intend to survey the 

 synthetic abihties of various organisms. 



For synthesis to occur an organism requires (1) inorganic 

 salts, (2) a source of carbon, (3) a source of nitrogen, and (4) a 

 source of energy. Table VII summarises sources of carbon, 

 nitrogen, and energy which are either commonly available in 

 nutrient media or which are known to be essential for the 

 growth of particular organisms. Some organisms can 

 synthesise all their protoplasm from simple sources such as 

 carbon dioxide and ammonia, plus a source of energy, and 

 must therefore be equipped with all the enzymes necessary 

 for the formation of the essentials of their existence from 

 these simple sources. This is not the case with all bacteria, 

 as many organisms are lacking in enzymes necessary for 

 certain synthetic processes. When this occurs the organism 

 in question is unable to synthesise some essential constituent 

 and is consequently unable to grow unless and until that parti- 

 cular constituent is supplied ready made in the environment. 

 When an organism has such a synthetic disability it is said 

 to be nutritionally "exacting" towards the substance which 

 it is unable to synthesise. It is by a study of the synthetic 

 disabilities of the more exacting organisms that we gain our 



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