EXTRACELLULAR SIGNAL MOLECULE(S) INVOLVED IN THE CARBON STARVATION RESPONSE OF MARINE VIBRIO SP. STRAIN S14

The role of exogenous metabolites as putative signal molecules mediati ng and/or regulating the carbon starvation adaptation program in Vibri o sp. strain S14 was investigated. Addition of the stationary-phase su pernatant extract (SSE) of Vibrio sp. strain S14 to logarithmic-phase cells resulted in a significant number of carbon starvation-induced pr oteins being up-regulated. Halogenated furanones, putative antagonists of acylated homoserine lactones (AHLs), inhibited the synthesis of pr oteins specifically induced upon carbon starvation. The effect of the furanone was the opposite of that caused by SSE with respect to the up -and do,vn-regulation of protein expression, indicating that both the furanone and the putative signalling molecules were acting on the same regulatory pathway. Culturability was rapidly lost when Vibrio sp. st rain S14 was starved in the presence of the furanone at a low concentr ation. The furanone also had a negative effect on the ability of carbo n-starved cells to mount resistance against UV irradiation and hydroge n peroxide exposure. The SSE of Vibrio sp. strain S14 had the ability to provide cross-protection against the loss in viability caused by th e furanone. We have further demonstrated that the SSE taken from low-a s well as high-cell-density cultures of Vibrio sp. strain S14 induced luminescence in Vibrio harveyi. Taken together, the results in this re port provide evidence that Vibrio sp. strain S14 produces extracellula r signalling metabolites during carbon and energy starvation and that these molecules play an important role in the expression of proteins c rucial to the development of starvation-and stress-resistant phenotype s.