AUTOMATIC ADJUSTMENT MECHANISMS 

 IN BACTERIAL CELLS 



A. C. R. Dean and Sir Cyril Hinshelwood 

 Physical Chemistry Laboratory, Oxford 



1. Introduction 



Variations in the growth cycle 



Unicellular organisms are inevitably exposed to changes of 

 environment sometimes the result of the vicissitudes of their 

 existence, sometimes the direct outcome of their own activity. 

 In many ways they can undergo adjustments minimizing the 

 adverse effects of the changed circumstances and tending to 

 maintain the functioning of the cell as near as possible to an 

 optimum. Such changes may have the appearance of being 

 purposeful, but are in fact automatic and are brought about 

 by the operation of what are in effect cybernetic mechanisms. 



In a very common set of laboratory conditions a small 

 number of cells are introduced into a medium of defined com- 

 position. They multiply, consuming nutrients, causing 

 changes in pH, sending toxic products into the surroundings, 

 and sometimes depleting the oxygen supply. Eventually 

 growth stops, only to be renewed when some of the cells are 

 again transferred to fresh medium. The sequence of events 

 constitutes a growth cycle. Throughout this cycle continuous 

 adjustments occur. 



Changing concentration of nutrients demands, in fact, little 

 compensation since the rate of growth is nearly independent 

 of the concentration of substrate until this concentration falls 

 to values in the region of 1 mg./l. The surface of the relevant 

 enzymes is usually saturated with substrate at concentrations 

 exceeding these very low values. 



Changed pH, changed nature of the nutrients, transfer from 



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