The serine protease autotransporter Tsh contributes to the virulence of Edwardsiella tarda.

The temperature-sensitive hemagglutinin (Tsh), identified as serine protease autotransporters of the Enterobacteriaceae (SPATEs) proteins, is an important virulence factor for avian-pathogenic Escherichia coli (APEC) and uropathogenic E. coli . However, little is known about the role of Tsh as a virulence factor in Edwardsiella tarda , a severe fish pathogen. In this study, we characterized the Tsh of E. tarda (named Tsh Et ) and examined its function and vaccine potential. Tsh Et is composed of 1224 residues and has three functional domains typical for autotransporters. Quantitative real-time reverse transcriptase-PCR analysis showed that expression of tsh Et was upregulated under conditions of high temperature, increased cell density, high pH, and iron starvation and during the infection of host cells. A markerless tsh in-frame mutant strain, TX01Δ tsh , was constructed to determine whether Tsh Et participates in the pathogenicity of E. tarda , Compared to the wild type TX01, TX01Δ tsh exhibited (i) retarded biofilm growth, (ii) decreased resistance against serum killing, (iii) impaired ability to block the host immune response, (iv) attenuated tissue and cellular infectivity. Introduction of a trans -expressed tsh gene restored the lost virulence of TX01Δ tsh . The passenger domain of Tsh Et contains a putative serine protease (PepS) that exhibits apparent proteolytic activity when expressed in and purified from E. coli as a recombinant protein (rPepS). When used as a subunit vaccine to immunize Japanese flounder, rPepS was able to induce effective immune protection. This is the first study of Tsh in a fish pathogen, and the results suggest that Tsh Et exerts pleiotropic effects on the pathogenesis of E. tarda . [ABSTRACT FROM AUTHOR]