Cloning, Expression And Functional Analysis Of Edwardsiella Tarda Sialidases

Bacterial sialidases are a class of glycosyl hydrolases that are known to play an importantrole in invasion of host cells and tissues. In this study, we examined in a model of Japaneseflounder (Paralichthys olivaceus) the potential function of NanA, a sialidase from the importantfish pathogen Edwardsiella tarda. NanA is composed of670residues and shares low sequenceidentities with known bacterial sialidases. In silico analysis indicated that NanA possesses asialidase domain and an autotransporter domain, the former containing five Asp-boxes, a RIPmotif, and the conserved catalytic site of bacterial sialidases. Purified recombinant NanA (rNanA)corresponding to the sialidase domain exhibited glycohydrolase activity against sialic acidsubstrate in a manner that is pH and temperature dependent. Mutation of nanA caused drasticattenuation in the ability of E. tarda to disseminate into and colonize fish tissues and to inducemortality in infected fish. Likewise, cellular study showed that the nanA mutant was significantlyimpaired in the infectivity against flounder macrophages. Immunoprotective analysis showedthat rNanA in the form of a subunit vaccine conferred effective protection upon flounder againstlethal E. tarda challenge. Together these results indicate that as a virulenee-rclated faetor, NanAplays an important role in the pathogenesis of E. tarda and may be exploited for the control of E.tarda infection in aquaculture.