Cloning, sequencing, and functional studies of the rpoS gene from Vibrio harveyi

The Vibrio harveyi rpoS gene which encodes an alternative sigma factor (σ s or σ 38), has been cloned and characterized. The predicted protein sequence is closely related to RpoS proteins in other bacteria with up to 86% sequence identity. A rpoS null mutant of V. harveyi was constructed and the phenotype studied. Comparison of the properties of the V. harveyi wild type and rpoS deletion mutant showed that rpoS affected the ability of the cells to survive only under specific types of environmental stresses. The rpoS null mutant had a lower survival rate compared to the wild type parental strain at high concentrations of ethanol and in the stationary phase. In contrast to other bacteria, deletion of rpoS in V. harveyi did not affect the resistance of the cells to high osmolarity or hydrogen peroxide, suggesting the existence of alternative systems in V. harveyi responsible for resistance to these stresses. RpoS appears not to be involved in the control of luminescence in V. harveyi even though it is implicated in regulation of other acyl-homoserine dependent quorum sensing systems.