Proline Over-Production Enhances Nitrogenase Activity Under Osmotic Stress in Klebsiella Pneumoniae
In 1955, J. H. B. Christian made the interesting observation that proline, added exogenously at low concentrations, specifically stimulated the growth rate (Christian, dy1955a,b) and respiration rate (Christian and Waltho, 1966) of some bacteria in media of inhibitory osmolarity. In order to test whether, in general, the accumulation of proline at high intracellular concentrations would directly result in enhanced osmotolerance, we isolated mutants of Salmonella typhimurium which over-produce proline (L. N. Csonka, manuscript in preparation). Some of the proline over-producing strains were indeed found to grow faster than the wild type organism in media of elevated osmolarity. These mutants were obtained as strains which were resistant to the toxic proline analogue: L-azetidine-2-carboxylic acid. The mutations in these strains were shown to be closely linked to proB + A + , the genes for the enzymes that catalyze the first two reactions of proline biosynthesis. The strain used for the isolation of the mutants was one in which the proB + A + region (of E. coli K12) was carried on an autonomously replicating, self-transmissible plasmid F’128. Therefore, the mutations conferring enhanced osmotolerance could be transferred easily to other strains of Salmonella typhimurium and related bacteria.
KeywordsKlebsiella Pneumoniae Osmotic Dehydration High Intracellular Concentration Nitrogen Fixation Activity Strain JL2468
Unable to display preview. Download preview PDF.