Abstract
Edwardsiella tarda is a broad-host pathogen that can infect mammals, reptiles, and fish. E. tarda exhibits a remarkable ability to survive in host serum and replicate in host phagocytes, but the underlining mechanism is unclear. In this study, in order to identify E. tarda proteins involved in serum resistance, iTRAQ proteomic analysis was performed to examine the whole-cell protein profiles of TX01, a pathogenic E. tarda isolate, in response to serum treatment. Of the differentially expressed proteins identified, one (named Sip2) possesses a conserved hydrogenase domain and is homologous to the putative hydrogenase accessory protein HypB. When Sip2 was expressed in Escherichia coli, it significantly enhanced the survival of the host cells in serum. Compared to TX01, the sip2 knockout, TX01Δsip2, was dramatically reduced in the ability of hydrogenase activity, serum resistance, intracellular replication, dissemination in fish tissues, and causing mortality in infected fish. The lost virulence capacities of TX01Δsip2 were restored by complementation with the sip2 gene. Furthermore, TX01Δsip2 was significantly reduced in the capacity to grow under low pHs and iron-depleted conditions, and was unable to maintain its internal pH in acidic environment. Taken together, these results indicate that Sip2 is a novel serum-induced protein that is essential to serum resistance, cellular and tissue infection, and coping with acidic stress via its ability to modulate intracellular pH.
Highlights
Edwardsiella tarda is a Gram-negative bacterium of the family Enterobacteriaceae
Identification of Sip2 and Characterization of Its Effect on Serum Resistance iTraq analysis indicated that compared to the untreated E. tarda TX01, TX01 treated with serum exhibited differential expression in 124 proteins (Supplementary Table S1)
We found that contact with fish serum significantly altered the expression of 124 proteins of E. tarda, suggesting that serum stress had a global effect on the expression of E. tarda proteins, which is consistent with the concept that complement-mediated immunity is a dire challenge that has to be coped with by the pathogen
Summary
Edwardsiella tarda is a Gram-negative bacterium of the family Enterobacteriaceae. It is a zoonotic pathogen with a broad host range that includes mammals, reptiles, and fish (Mohanty and Sahoo, 2007; Leung et al, 2012). E. tarda is known to infect a large number of freshwater and marine fish including flounder, turbot, tongue sole, and tilapia (Matsuyama et al, 2005; Katharios et al, 2015; Wang and Sun, 2015; Zeng et al, 2017). E. tarda is counted one of the most severe fish pathogens. E. tarda is a human pathogen and has been reported to cause acute gastroenteritis, meningitis, septicemia, and wound infections in humans (Nelson et al, 2009; Park et al, 2012; Crosby et al, 2013; Suezawa et al, 2016).
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