Hfq, a global regulator contributes to the virulence of Vibrio splendidus AJ01

Abstract Hfq acts as an RNA-binding protein that ubiquitously exists in bacteria and contributes to global regulation of a wide range of gene expression. Vibrio splendidus is an important pathogen of sea cucumber Apostichopus japonicus, therefore, an hfq gene mutant strain, Δhfq, was constructed to explore its regulation on the virulence of V. splendidus. Our result showed that both the growth and virulence of Δhfq were reduced. To further reveal the pathways regulated by Hfq, the difference in transcriptomics between wild type and Δhfq was analyzed. Results showed that the expression of more than 1/8 of the total genes was affected by Hfq. KEGG analysis showed that the differentially expressed genes in Δhfq were enriched mainly in the bacterial secretion system, quorum sensing system, bacterial biofilm formation and flagellar assembly system, which were commonly related to virulence. Six genes in chemotaxis pathway (cheA, cheB, cheR, cheV, cheY and mcp) and twelve genes in flagellar assembly pathway (flgK, flgF, flgI, fliD, fliC, flgE, flgD, motY, flgG, flgB, flgC and fliS) were significantly down-regulated in Δhfq. Consistent with the transcriptomic analysis, the flagellum of Δhfq was almost undetectable under transmission electron microscopy. The main virulence-related factors of adhesion ability, biofilm formation and swimming motility that were regulated by chemotaxis and flagellar assembly were all attenuated in Δhfq. In conclusion, Hfq contributes to the virulence of V. splendidus AJ01 mainly through its positive regulation of adhesion, biofilm formation, and swimming motility via flagellar assembly system and chemotaxis system.