Influence of Environment on the Content and Composition of Microbial Free Amino Acid Pools

Abstract

SUMMARY: The free amino acid pool contents of Gram-negative bacteria (Aerobacter aerogenes, Erwinia carotovora, Pseudomonas fluorescens) were studied as functions of the growth environment and were compared with those from correspondingly grown cultures of Gram-positive bacteria (Bacillus subtilis var. niger, B. megaterium, B. polymyxa) and the yeast Saccharomyces cerevisiae. Although the pools of the Gram-positive bacteria and the yeast contained five to 20 times the concentration of free amino acids present in the pools of Gram-negative bacteria, all pools were similar in containing only a limited range of detectable amino acids. Glutamate invariably predominated and generally accounted for over 50% of the total amino acid content of the pool. The contents and composition of pools from micro-organisms maintained in steady states in chemostat cultures did not vary with time, but changed significantly with changes in either growth rate or the nature of the growth limitation. However, these pool variations were small compared with those resulting from addition of 2% (w/v) NaCl to a culture of growing bacteria. With cultures of Gram-negative bacteria, sudden changes in medium salinity effected marked and rapid changes in free glutamate content; with Gram-positive bacteria, similar changes occurred, but extremely slowly. Addition of 4% (w/v) NaCl to growing yeast cultures brought about no observed changes in pool size or composition. These results are discussed with reference to the involvement of free amino acids in synthesis and functioning of microorganisms.