The Role of Proline in Osmoregulation in Salmonella Typhimurium and Escherichia Coli
A variety of strategies have evolved for the regulation of the internal osmotic strength of organisms, but the details of these osmoregulatory mechanisms are poorly understood. In bacteria, internal osmolarity is maintained mainly by the accumulation of amino acids (3,10,16) and inorganic ions (4,9), such that it exceeds the osmolarity of the growth medium. A discovery made a quarter of a century ago by J. H. B. Christian suggested that proline has a special role in osmoregulation: in media of inhibitory osmolarity the growth and respiration rates of Salmonella orianenburg were stimulated specifically by the addition of proline (5,6). Using this observation as motivation, we have selected proline overproducing mutants of Salmonella typhimurium and found that some, as a result, have acquired an increased growth rate in media of inhibitory osmolarity (8; L. Csonka, manuscript in preparation). We found that in these proline over-producing mutants, the intracellular proline levels were regulated such that they increased with increasing osmotic stress. Here, we present experimental results which suggest that in the over-producing mutants, and in wild type strain, the proline permeases play an important role during osmotic stress for the regulation of the intracellular proline levels.
KeywordsOsmotic Stress Glutamate Dehydrogenase Free Proline Osmotic Dehydration Amino Acid Pool
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