The minimum low-salt stimulon in Vibrio parahaemolyticus

Global gene expression profiles of V. parahaemolyticus grown under 2% and 0.66% NaCl were compared to define the minimum low-salt stimulon. The ectABC-lysC operon for synthesis of the compatible solute ectoine, as well as three compatible-solute transport systems, namely ProU (glycine betaine), OpuD1 (glycine betaine) and Pot2 (spermidine), was up-regulated under 2% NaCl in relative to 0.66% NaCl. The 2% NaCl condition favored the inducible expression of OmpW, OmpN and OmpA2, while repressed the expression of OmpA1, OmpU and VP1008. These results indicated that, to master the hyperosmotic stress of saline environments, V. parahaemolyticus might not only accumulate osmoprotectants through uptake or endogenous synthesis of compatible solutes, but also remodel its profiles of outer membrane protein to restore its cell membrane. The above differentially regulated genes will provide novel candidates for the further investigation of the molecular mechanisms of osmoadaptation in V. parahaemolyticus. A cDNA microarray imprinted with 4669 genes representing about 97% of V. parahaemolyticus genome was used for transcriptome analysis . For two-sample (reference vs. test) microarray hybridization, four independent bacterial cultures from each condition were prepared as biological replicates for RNA isolation . Accordingly, for each time point, four dual-fluorescence-labeled cDNA probes were prepared to hybridize with four slides, respectively. Pairwise comparisons were made using dye swaps to avoid labeling bias. A ratio of mRNA levels (test/reference) was calculated for each gene. Significant changes of gene expression were identified with the SAM software . After the SAM analysis, only genes with at least 2-fold changes in expression were collected for further analysis.