A comparative study of low-pH tolerance and chitinase activity between toxigenic and non-toxigenic strains of Vibrio cholerae
摘要
Survival of toxigenic and non-toxigenic strains of Vibrio cholerae involves adaptation to varying pH conditions, a mechanism which is poorly understood. Chitinase activity, which is essential for survival both inside and outside its human host at various pH levels, is not thoroughly profiled. We report on the growth and chitinase activity of two clinical isolates of V. cholerae: VC20, a ctx+ strain, and WO5, a ctx− strain, at different pH. We compared the expression of key genes between these strains. WO5, the non-toxigenic strain, showed robust growth and higher chitinase activity across a wide pH range compared to VC20. WO5 expressed higher ompK and toxT transcripts, implicated in host cell adhesion and virulence, respectively. We propose that lower hapR levels in WO5, in contrast to VC20, are key to its low-pH tolerance. A sequence-based homology search revealed a widespread presence of low-pH adaptation modules – lysine-cadaverine and ornithine-putrescine – in multiple representative species of the Vibrio genus. Further, the loss of a nitrite reductase gene, which confers low-pH tolerance, is specific to V. cholerae and V. mimicus. We propose that hapR expression and other low-pH adaptation factors reported here could be molecular predictors of low-pH tolerance in toxigenic and non-toxigenic V. cholerae.