Proline over-production results in enhanced osmotolerance in Salmonella typhimurium

Mutants of S. typhimurium with enhanced osmotolerance were isolated. These mutants were obtained as strains which over-produced proline due to regulatory mutations affecting proline biosynthesis. The mutations are located on F'proBa and upon transfer to other S. typhimurium strains, they confer enhanced osmotolerance on the recipients. The osmotolerant mutants not only have higher intracellular proline levels than the osmosensitive parental strain, but the proline levels in the osmotolerant mutants are regulated such that they increase in response to osmotic stress. Possibly reasons why elevated proline levels lead to enhanced osmotolerance are discussed.