The Role of L-Proline in Response to Osmotic Stress in Salmonella Typhimurium: Selection of Mutants with Increased Osmotolerance as Strains which Over-Produce L-Proline

Abstract

When bacteria of a wide variety of species are stressed by high osmolarity in the growth medium, a common response they exhibit is that there is a pronounced elevation in the intracellular concentration of free L-proline, or L-glutamate, or, in a few instances, γ-amino butyric acid.1 In a number of cases in which the bacteria were grown in the absence of exogenously added amino acids this accumulation was due to the enhanced net rate of synthesis of these metabolites (Tempest et al-, 1970; Brown and Stanley, 1972; Makemson and Hastings, 1979), but in others, in which the cells were grown in a complex media it was not clear whether the increases in concentration were due to the stimulation of the synthesis or uptake of these compounds (Measures, 1975; Koujima et al., 1978). It was shown by Britten and McClure,(1962) that in E. coli the accumulation of L-proline the medium is stimulated in direct proportion to the external osmolarity. An explanation offered for the elevation of the concentration of these compounds is that it serves to balance the intracellular osmolarity against the osmolarity of the growth medium (Brown and Stanley, 1972; Measures, 1975).