HtpG is involved in the pathogenesis of Edwardsiella tarda.

Hsp90 is a molecular chaperone that is involved in diverse cellular processes including protein folding/repairing and signal transduction. Edwardsiella tarda is a serious fish pathogen that affects fish aquaculture worldwide. The aim of this study was to investigate the potential importance of HtpG, the prokaryotic homologue of Hsp90, in the pathogenesis of E. tarda. E. tarda HtpG is 627-residue in length and contains domain structures that are conserved among Hsp90 family members. Quantitative real time RT-PCR analysis indicated that expression of htpG is induced by heat shock and oxidative stress. Recombinant HtpG (rHtpG) purified from Escherichia coli exhibits apparent ATPase activity, which is optimal at 40°C. Mutation of htpG (i) affects bacterial growth at elevated temperature and renders the cells more sensitive to stress induced by reactive oxygen species, (ii) causes dramatic reduction in blood dissemination and general bacterial virulence, (iii) weakens the ability of E. tarda to block head kidney macrophage activation and to resist against the bactericidal effect of macrophages, and (iv) upregulates the expression of pro-inflammatory cytokines in macrophages. Taken together, these results indicate that HtpG is a biologically active protein that is required for E. tarda to cope with various stress conditions especially that encountered in vivo the host system during infection.