Proteins variations in Listeria monocytogenes exposed to high salinities

Listeria monocytogenes Scott A grown in the minimal chemically defined medium M6LT was challenged to a concentration of either 35 or 65 g l−1 of NaCl for 1 h in the presence of a [35S]cysteine–[35S]methionine labelling mix. The protein patterns were analysed by 2D-electrophoresis in the two conditions and isoosmotic condition (5 g l−1 of NaCl in M6LT). A great number of proteins which were synthesized under isoosmotic conditions were either completely repressed or expressed at a reduced level, at 65 g l−1 and to a lesser extent at 35 g l−1 of NaCl. At 35 g l−1 of NaCl, six proteins were up-regulated, five proteins showed no change in expression level and five were repressed. Among the proteins up-regulated at 35 g l−1 of NaCl, a single one (18.7 kDa, pI 5.05) was up-regulated at 65 g l−1 too. We observed 21 proteins which were repressed at 65 g l−1 of NaCl, among which 11 completely disappeared. Some of the up-regulated proteins have characteristics of molecular weight and isoelectric point close to those of stress proteins reported elsewhere: the protein induced both at 35 and 65 g l−1 might correspond to a previously proposed universal stress protein of Listeria. Some proteins which were repressed at 65 g l−1 have molecular weights close to those of virulence proteins.