CHAPTER VI 



ABSORPTION OF AMINO-ACIDS BY 

 MICRO-ORGANISMS 



The amino-acids required for growth are either synthesized 

 by the organism itself or derived from its environment. 

 Consequently the mechanisms controlling the absorption of 

 amino-acids are of fundamental importance, especially to 

 exacting organisms who must perforce rely entirely on their 

 environment for supplies of compounds which they are un- 

 able to synthesize. The factors influencing the passage of 

 amino-acids into and out of micro-organisms, particularly 

 those exacting towards amino-acids, have been investigated 

 by Gale and his colleagues [6]. Whilst using the bacterial 

 decarboxylases [4] (p. 27) for the analysis of the amino-acid 

 composition of bacterial proteins [3], Gale found that 

 Gram-positive bacteria contained large amounts of free 

 amino-acids. This discovery arose from the fact that hydro- 

 lysates of whole cells, and not isolated proteins, were being 

 analysed, and it was realized that serious errors would result 

 if there were appreciable amounts of free amino-acids in 

 the experimental material prior to hydrolysis. Such amino- 

 acids might be adsorbed on to the cell surface or be present 

 inside the cells. In order to determine the significance of 

 these possibilities, washed cells of Strep, faecalis were dis- 

 integrated by shaking with glass beads, a procedure which 

 ruptured the cells but caused no significant degradation of 

 the proteins. Analysis of the disintegrated cells revealed the 

 presence of relatively high concentrations of certain amino- 

 acids (cf. columns h and a—hm Table 6.1). Although the 

 latter were also found in disintegrated cells of Staph, aureus, 

 there were no significant amounts in those of two Gram- 

 negative organisms, Esch. colt and Aerobacter aerogenes [5]. 

 Further experiments showed that the greater proportion of 

 these amino-acids was located inside the cells. 



There was therefore an indication that only Gram- 

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