THE ROLE OF PEPTIDE METABOLISM IN THE GROWTH OF LISTERIA-MONOCYTOGENES ATCC-23074 AT HIGH OSMOLARITY

The growth of Listeria monocytogenes ATCC 23074 in defined medium is s ensitive to high osmolarity when compared with its growth in complex m edia, such as brain heart infusion (BHI). The two major contributors t o this difference in growth rate are the availability in BHI of the os moprotectant glycine betaine and peptides. Peptone plays two major rol es: firstly as a nutritional supplement for protein synthesis, and sec ondly as a source of amino acids and peptides that serve as a mechanis m of maintaining turgor. In the presence of peptone the total amino ac id pool at high osmolarity is substantial and even in the presence of glycine betaine the amino acid pool makes a major contribution to turg or maintenance. At high osmolarity there is a general increase in amin o acid pools, with particularly substantial pools of glutamate, aspart ate, proline, hydroxyproline and glycine. Peptides are also accumulate d by cells from the peptone supplied in the medium, Glycine-containing peptides are accumulated in the cytoplasm under all conditions. Speci fic glycine- and proline-containing peptides stimulate growth at high osmolarity. The peptide prolyl-hydroxyproline accumulates in cells to high levels in response to growth at high osmolarity, and the pools of the derived amino acids also show a dependence on the external osmoti c pressure. However, proline only confers significant osmoprotection w hen supplied as peptides. The significance of these data in the contex t of the occurrence of L. monocytogenes in foods with high peptide con tent is discussed.