Relative changes in incorporation rates of leucine and methionine during starvation survival of two bacteria isolated from marine waters

Two copiotrophic Gram-negative bacteria isolated from marine waters, S14 and Vibrio sp. DW1, were examined for changes in the rate of protein synthesis in the initial phase of energy and nutrient deprivation. The incorporation of [³H] leucine into the trichloroacetic acid (TCA)-insoluble material was examined as a method for estimating rates of protein synthesis. The incorporation of methionine was measured and compared with the results of leucine incorporation. Protein synthesis was demonstrated throughout a period of 120 h of starvation. The incorporation rate was related to the time of starvation and decreased subsequent to an initial increase during the first few hours of dormancy. Control experiments with proteinase K and chloramphenicol demonstrated that the labelled amino acids were preferentially incorporated into proteins. It was also demonstrated that the uptake of amino acids was not a rate-limiting step. During the first hours of starvation the ratio of the protein to the dry weight of the S14 cells increased parallel to the increase in the amino acid incorporation rate. The increased activity of the protein-synthesising system during the first hours of nutrient and energy depletion indicates the presence of an active cellular response to the downshift conditions. Furthermore, these findings are consistent with the increased respiratory activity during the first hours of starvation, which has previously been observed for the bacteria examined in this study.