Edwardsiella tarda Sip2: A Serum-Induced Protein That Is Essential to Serum Survival, Acid Resistance, Intracellular Replication, and Host Infection

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.

HutZ is required for biofilm formation and contributes to the pathogenicity of Edwardsiella piscicida

“…The results showed that the amount of TX01Δ hutZ recovered from the entire (i.e., from the surface and the intracellular milieu) FG cell culture was significantly lower than that of TX01 after infecting for 1 h and 2 h (Figure 9A). It is known that E. piscicida is able to survive and replicate in host cells [29]. To examine whether the hutZ Ep mutation played any role in the intracellular survival of TX01, FG cells were incubated with E. piscicida , and extracellular bacteria were killed.…”

“…Chen et al [28] found that E. piscicida tunes the tricarboxylic acid cycle to evade complement-mediated killing, which reveals a previously unknown membrane potential-dependent mechanism of serum resistance. Two novel serum-induced proteins, Sip1 and Sip2, were found to be essential to serum resistance, which are also different from known mechanisms [29, 51]. Other virulence factors involved in resistance against the bactericidal effect of hos serum include the serine protease autotransporter Tsh, lysozyme inhibitor Ivy, and thioredoxin TrxH [34, 39, 52].…”

Edwardsiella piscicida: A versatile emerging pathogen of fish

“…Sip1, also named as Aur or aureolysin, is a seruminduced zinc metalloprotease implicated in serum resistance and is essential for fish infection [95]. In addition, Sip2 (homologue of HypB, a putative hydrogenase) protects E. piscicida in fish serum and significantly increases cellular and tissue infection by allowing the bacteria to cope with acidic stress [96]. Although the direct regulon is unclear, the cyclic AMP receptor protein (CRP) was shown to be essential for flagellar biosynthesis and motility, hemolytic activity, and in vivo virulence in E. piscicida [97].…”

Thioredoxin H (TrxH) contributes to adversity adaptation and pathogenicity of Edwardsiella piscicida

“…In this study, we also examined the effect of trxH Ep on E. piscicida pathogenicity. It is known that biofilm formation and serum resistance are important parts of the virulence in multiple pathogens such as E. piscicida [17, 35] and H. pylori [48, 49]. In the latter, the inability to acquire iron from serum has been suggested to block H. pylori virulence by weakening its growth and survival in the serum [48].…”

“…Cheng et al reported that this bacteria uses the tricarboxylic acid cycle to evade complement-mediated killing [16]. Another study showed that Sip2 in E. piscicida contributes to serum survival, acid resistance, intracellular replication, and host infection [17]. However, studies on the tolerance of E. piscicida to oxidative stress are limited.…”