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Edwardsiella piscicida (E. piscicida) is a common pathogen in freshwater and marine environments and an important intestinal pathogen of fish. Fucose large presence in the intestines could possibly regulate relevant genes to promote bacterial infectivity. In this study, the wild-type E. piscicida and the fucP gene-deleted strain ΔfucP were used to identify its virulence-regulating pathway and colonization. The results showed that the gene transcription levels of key FusKR and type III secretion system (T3SS) in E. piscicida were upregulated by different concentrations of fucose. Both the wild-type and the ΔfucP strain grew faster with 30 mM fucose added than that without fucose added. In addition, the penetration of the wild-type E. piscicida with fucose added was significantly stronger than that of both ΔfucP with fucose and the wild-type E. piscicida without fucose. Meanwhile, the gene transcription levels of T3SS-related genes eseB, eseC, eseD, eseE, and eseG in E. piscicida were significantly downregulated after the fucP gene mutant. Finally, tilapia infected with the wild-type strain showed a significant increase in the E. piscicida colonization compared to those infected with the mutant strain. All results indicate that FucP of E. piscicida mediated fucose to promote the growth, motility, and intestinal colonization in tilapia.

Edwardsiella piscicida (E. piscicida) is an important fish pathogen. However, the mechanism of Glu6P transport regulatory protein UhpA how to affect the virulence gene expression in E. piscicida is still unclear. The results in this study showed that the metabolism-related gene expression of cysteine synthase (orf 1134) and sulphate transporter (ychM) in the uhpA mutant strain ΔuhpA was 0.76-fold and 0.68-fold lower than the ones in the wild strains (p < .05). The gene expression of ethA and ethB in the ΔuhpA strain was 0.80-fold and 0.72-fold lower than the ones in the wild strains (p < .05). However, the gene expression of fliC and flgN in the ΔuhpA was 1.51-fold and 1.21-fold higher than the ones in the wild strains (p < .05). The gene expression of T3SS (esrB and esrC) and T6SS (evpB and evpC) in the ΔuhpA was 1.27-fold, 1.13-fold, 1.28-fold and 1.23-fold higher than the ones in the wild strains (p < .05). This suggested that the uhpA gene could regulate the key virulence gene expression, and the uhpA gene was associated with the pathogenicity of E. piscicida in fish.

Edwardsiella piscicida (E. piscicida) is an important zoonotic pathogen that infects fish by colonizing the intestines. The intestine provides nutrition including Glucose 6-phosphate (Glu6P) and a competitive environment for the microbiota. Although the transport system regulatory protein gene uhpA has been reported in E. piscicida genomes, whether the uhpA gene is involved in the pathogenicity of E. piscicida remains largely unknown. Therefore, the uhpA gene mutants strain E. piscicida ΔuhpA was constructed to elucidate the functions of Glu6P and the uhpA gene in E. piscicida. The results demonstrated that Glu6P significantly increased the gene expression of uhpC/uhpB/uhpA than without adding Glu6P in the culture. The gene expression of uhpC and uhpB was down regulated in the mutant strain than that of in the wild type strain. E. piscicida ΔuhpA exhibited an increase in virulence compared to that of E. piscicida EIB202 [LD50 value: (3.98 × 106 CFU/fish) and LD50 value: (1.45 × 107 CFU/fish) respectively]. Besides, although TNF-α did not show significant differences (p > 0.05) in the spleen of tilapia infected with ΔuhpA and EIB202 in the whole observed period, the gene expression of IL-1β and TGF-β in the spleen of tilapia infected with ΔuhpA showed significantly higher (p

Edwardsiella piscicida (E. piscicida) is one of the main pathogens of fish, which could invade the host through the gut. Glucose 6-phosphate (Glu6P) within the gut provides environmental stresses that affect the pathogenicity of bacteria. Here we focus on a novel two-component chemical signal transduction system, named UhpB/UhpA in E. piscicida, including the key component hexose phosphate transport system regulatory protein (UhpA) coded by the uhpA gene. This study will elucidate the functions of the uhpA gene in the pathogenicity of E. piscicida and the immune response in zebrafish when infected with E. piscicida. The results showed that the wild type strain of E. piscicida EIB202 demonstrated significant increases in growth compared to the mutant strain ΔuhpA with or without 20 mM Glu6P (P < 0.05). The LD₅₀ of E. piscicida △uhpA strain (2 × 10⁴ CFU/fish) for zebrafish was significantly lower than the wild-type strain (1 × 10⁵ CFU/fish), which suggested the uhpA gene deletion could increase its virulence. Besides, fish infected with ΔuhpA showed significantly higher (p < 0.05) gene expression of IL-1β and TGF-β in spleen than fish infected with EIB202 at 6 h, 12 h, 24 h, and 48 h after infection, TNF-α in spleen of fish infected with ΔuhpA showed significantly higher (p < 0.05) than fish infected with EIB202 at 24 h, 48 h, and 72 h after infection, and IFN-γ in spleen of fish infected with ΔuhpA showed significantly higher (p < 0.05) than fish infected with EIB202 at 12 h, 24 h and 72 h after infection. In summary, these results suggest that the uhpA gene deletion in E. piscicida affects Glu6P usage; most important, which could enhance the pathogenicity of E. piscicida in zebrafish, particularly increase the induction of the gene expression of IL-1β, TNF-α, IFN-γ and TGF-β in the spleens of zebrafish after infection.

Edwardsiella piscicida (E. piscicida) is an important zoonotic pathogen, which infects animals by colonizing the intestine. Glucose 6-phosphate (Glu6P) was an important carbohydrate in intestine and could be used as a regulate signal. Here we identify a virulence-regulating pathway named Glu6P transport regulatory protein UhpA, which affects the virulent genes of hemolysins, flagellar, T3SS, T6SS and metabolism related genes how to promote E. piscicida infect the host. The results showed that the metabolism related gene expression of cysteine synthase (orf 1134) and sulfate transporter (ychM) in the uhpA mutant strain ΔuhpA was 0.76-fold and 0.68-fold lower than the ones in the wild strains (P < 0.05), the gene expression of ethA and ethB in the ΔuhpA strain was 0.80-fold and 0.72-fold lower than the ones in the wild strains (P < 0.05). However, the gene expression of fliC and flgN in the ΔuhpA was 1.51-fold and 1.21-fold higher than the ones in the wild strains (P < 0.05), the gene expression of T3SS (esrB and esrC) and T6SS (evpB and evpC) in the ΔuhpA was 1.27-fold, 1.13-fold 1.28-fold and 1.23-fold higher than the ones in the wild strains (P < 0.05). Besides, the survival rate of fish challenged with E. piscicida EIB202 and ΔuhpA was 50% and 30% respectively. These suggested that although the uhpA gene deletion decreased the metabolic level and the hemolysins related gene expression in E. piscicida, the uhpA gene could down regulate the key virulent gene expression to decrease the pathogenicity of E. piscicida in fish.

Edwardsiella piscicida (E. piscicida) is a significant bacterial pathogen of cultured fish, which infected fish meanly through the intestine. Glucose 6-phosphate (Glu6P) in the intestine is nutritious to the pathogen, Meanwhile, Glu6P was found using as a virulent regulating signal for bacteria. The UhpA, one of the Glu6P transport system regulatory proteins could down-regulate the uhpC/uhpB/uhpA system and decrease its pathogenicity. However, the motility and the colonization of E. piscicida affected by UhpA were still unclear. In this study, the motility and the colonization of E. piscicida were monitored. The result demonstrated that the motility of EIB202 was significantly stronger than that of in ΔuhpA according to fractions 4, 8 and 9. However, the motility of ΔuhpA was significantly stronger than that of EIB202 according to the total number at the whole experiment. Although, there was no difference in the number of bacteria in the posterior intestine of tilapia after infected with E. piscicida EIB202 and ΔuhpA. The number of bacteria in the anterior and the middle intestine of fish infected with ΔuhpA were significantly higher than that of in fish infected with EIB202 at the whole experiment (P