8 BACTERIA AS CHEMICAL AGENTS 



It will be seen as we go along that it is often possible to 

 predict how a given organism may react to a given chemical 

 environment or how to arrange the chemical environment in 

 such a way that bacteria might be expected to carry out a 

 desired chemical task — although only experiment will tell 

 whether they will actually do so. 



Before embarking on this problem we must first have some 

 understanding of the reasons why bacteria attack their 

 environment at all. When an organism is inoculated into a 

 suitably nutrient medium, it begins to grow, synthesising 

 new bacterial protoplasm with consequent increase in size 

 until eventually division takes place with the formation of 

 two cells from one. The rate at which subsequent divisions 

 occur depends to a large extent upon the nature of the medium 

 but an organism such as Escherichia coli living in a rich 

 medium such as a tryptic digest of casein can divide once 

 every ten or fifteen minutes. At this rate one organism can 

 give rise to over one million organisms in five hours. Con- 

 sequently one organism can synthesise over one million times 

 its own weight of bacterial protoplasm in five hours. This 

 high rate of synthesis must take place at the expense of the 

 environment which has to supply all the raw materials 

 including major requirements of carbon and nitrogen; minor 

 requirements of phosphorus, sulphur, and iron, and traces of 

 many other elements. Since these elements may be present 

 in the medium in a form not primarily utilisable by the 

 organism, it must attack the complex substances present in 

 the medium so as to render the raw materials available in an 

 assimilable and utiHsable form. Secondly, the synthesis of 

 this chemical complex of the bacterial cell involves the 

 expenditure of energy and this the organism obtains by the 

 degradation of energy-rich substances in the environment. 

 Thirdly, if the physico-chemical properties of the environment 

 vary to any significant extent during the synthesis, then the 

 organism reacts by speeding up those reactions tending to 

 stabilise the internal environment. For example, the decom- 

 position of carbohydrate for energy purposes usually results in 



