GLOBAL ANALYSIS OF THE CARBON STARVATION RESPONSE OF A MARINE VIBRIO SPECIES WITH DISRUPTIONS IN GENES HOMOLOGOUS TO RELA AND SPOT

The stringent control response, which involves a rapid accumulation of ppGpp, is triggered if the marine Vibrio sp. strain S14 is subjected to carbon and energy starvation. By means of high-resolution two-dimen sional gel electrophoresis analysis, we addressed the role of the majo r ppGpp-synthesizing enzyme (RelA) in the regulation of the carbon sta rvation response of vibrio sp. strain S14. The finding that a large nu mber of the carbon starvation-induced proteins were underexpressed in the Vibrio sp. S14 relA mutant strain after the onset of glucose starv ation suggests that a rapid accumulation of ppGpp is required for indu ction of many of the carbon starvation-induced proteins. However, it w as also found that a majority of the carbon starvation-induced protein s were significantly less induced if the stringent control response wa s provoked by amino acid starvation. We therefore also addressed the n otion that a carbon starvation-specific signal transduction pathway, c omplementary to the stringent control, may exist in Vibrio sp, strain S14. It was found that a majority of the proteins that were underexpre ssed in the relA mutant strain were also underexpressed in the Vibrio sp. S14 spoT mutant strain (csrS1). Interestingly, a large proportion of these underexpressed proteins were found to belong to a group of pr oteins that are not, or significantly less, induced by starvation cond itions that do not promote starvation survival. On the basis of these observations and the finding that the csrS1 strain survives poorly but accumulates ppGpp in a fashion similar to the wild type during carbon and energy source starvation, the gene product of the csrS gene is su ggested to be responsible for the mediation of a signal which is compl ementary to ppGpp and essential for the successful development of the starvation- and stress-resistant cell. This conclusion was also suppor ted by experiments in which changes in phenotypic characteristics know n to be induced during carbon starvation were studied. The starvation induction of the high-affinity glucose uptake system was found to be d ependent on the csrS gene but not relA, and the synthesis of carbon st arvation-specific periplasmic space proteins was dependent, at differe nt times of starvation, on both the relA and the csrS gene products.