The GntR-like transcriptional regulator HutC involved in motility, biofilm-forming ability, and virulence in Vibrio parahaemolyticus

TssL2 of T6SS2 is required for mobility, biofilm formation, wrinkly phenotype formation, and virulence of Vibrio parahaemolyticus SH112

Type VI secretion system 2 (T6SS2) of Vibrio parahaemolyticus is required for cell adhesion and autophagy in macrophages; however, other phenotypes conferred by this T6SS have not been thoroughly investigated. We deleted TssL2, a key component of T6SS2 assembly, to explore the role of the T6SS2 in environmental adaptation and virulence. TssL2 deletion reduced Hcp2 secretion, suggesting that TssL2 played an important role in activity of functional T6SS2. We found that TssL2 was necessary for cell aggregation, wrinkly phenotype formation, and participates in motility and biofilm formation by regulating related genes, suggesting that TssL2 was essential for V. parahaemolyticus to adapt changing environments. In addition, this study demonstrated TssL2 significantly affected adhesion, cytotoxicity, bacterial colonization ability, and mortality in mice, even the levels of the proinflammatory cytokines IL-6 and IL-8, suggesting that TssL2 was involved in bacterial virulence and immunity. Proteome analysis revealed that TssL2 significantly affected the expression of 163 proteins related to ABC transporter systems, flagellar assembly, biofilm formation, and multiple microbial metabolism pathways, some of which supported the effect of TssL2 on the different phenotypes of V. parahaemolyticus. Among them, the decreased expression of the T3SS1 and T2SS proteins was confirmed by the results of gene transcription, which may be the main reason for the decrease in cytotoxicity. Altogether, these findings further our understanding of T6SS2 components on environmental adaption and virulence during bacterial infection. KEY POINTS: • The role of T6SS2 in V. parahaemolyticus was far from clear. • TssL2 participates in cell aggregation, wrinkly phenotype formation, motility, and biofilm formation. • TssL2 is essential for cell bacterial colonization, cytotoxicity, virulence, and proinflammatory cytokine production.

CalR Inhibits the Swimming Motility and Polar Flagellar Gene Expression in Vibrio parahaemolyticus

Vibrio parahaemolyticus has two flagellar systems, the polar flagellum and lateral flagella, which are both intricately regulated by a multitude of factors. CalR, a LysR-type transcriptional regulator, is sensitive to calcium (Ca) and plays a crucial role in regulating the virulence and swarming motility of V. parahaemolyticus. In this study, we have demonstrated that the deletion of calR significantly enhances the swimming motility of V. parahaemolyticus under low Ca conditions but not under high Ca conditions or in the absence of Ca. CalR binds to the regulatory DNA regions of flgM, flgA, and flgB, which are located within the polar flagellar gene loci, with the purpose of repressing their transcription. Additionally, it exerts an indirect negative control over the transcription of flgK. The overexpression of CalR in Escherichia coli resulted in a reduction in the expression levels of flgM, flgA, and flgB, while having no impact on the expression of flgK. In summary, this research demonstrates that the negative regulation of V. parahaemolyticus swimming motility by CalR under low Ca conditions is achieved through its regulation on the transcription of polar flagellar genes.

H-NS-Mediated Regulation of Swimming Motility and Polar Flagellar Gene Expression in Vibrio parahaemolyticus

Vibrio parahaemolyticus is equipped with two distinct flagellar systems: a polar flagellum and numerous lateral flagella. The polar flagellum plays a role in propelling swimming in liquids, while the lateral flagella serve to enhance swarming on surfaces or in viscous environments. H-NS is a histone-like nucleoid structuring protein that plays a regulatory role in both the swimming and swarming motility of V. parahaemolyticus. However, the detailed mechanisms have not been fully understood. In this study, we have demonstrated that the deletion of hns hindered the growth rate of V. parahaemolyticus during the logarithmic growth phase and significantly decreased the swimming motility. H-NS directly activated the transcription of flgMN, flgAMN, flgBCDEFGHIJ, and flgKL-flaC located within the polar flagellar gene clusters. The expression of H-NS in Escherichia coli led to a marked elevation in the expression levels of flgM, flgA, flgB, and flgK, suggesting the positive effect of H-NS on the expression of polar flagellar genes in E. coli. This work demonstrates that the positive regulation of H-NS on the swimming motility in V. parahaemolyticus may be achieved through its regulation of polar flagellar gene expression and bacterial growth.

BolA-like protein (IbaG) promotes biofilm formation and pathogenicity of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a gram-negative halophilic bacterium widespread in temperate and tropical coastal waters; it is considered to be the most frequent cause of Vibrio-associated gastroenteritis in many countries. BolA-like proteins, which reportedly affect various growth and metabolic processes including flagellar synthesis in bacteria, are widely conserved from prokaryotes to eukaryotes. However, the effects exerted by BolA-like proteins on V. parahaemolyticus remain unclear, and thus require further investigation. In this study, our purpose was to investigate the role played by BolA-like protein (IbaG) in the pathogenicity of V. parahaemolyticus. We used homologous recombination to obtain the deletion strain ΔibaG and investigated the biological role of BolA family protein IbaG in V. parahaemolyticus. Our results showed that IbaG is a bacterial transcription factor that negatively modulates swimming capacity. Furthermore, overexpressing IbaG enhanced the capabilities of V. parahaemolyticus for swarming and biofilm formation. In addition, inactivation of ibaG in V. parahaemolyticus SH112 impaired its capacity for colonizing the heart, liver, spleen, and kidneys, and reduced visceral tissue damage, thereby leading to diminished virulence, compared with the wild-type strain. Finally, RNA-sequencing revealed 53 upregulated and 71 downregulated genes in the deletion strain ΔibaG. KEGG enrichment analysis showed that the two-component system, quorum sensing, bacterial secretion system, and numerous amino acid metabolism pathways had been altered due to the inactivation of ibaG. The results of this study indicated that IbaG exerts a considerable effect on gene regulation, motility, biofilm formation, and pathogenicity of V. parahaemolyticus. To the best of our knowledge, this is the first systematic study on the role played by IbaG in V. parahaemolyticus infections. Thus, our findings may lead to a better understanding of the metabolic processes involved in bacterial infections and provide a basis for the prevention and control of such infections.

QsvR represses the transcription of polar flagellum genes in Vibrio parahaemolyticus

Vibrio parahaemolyticus produces dual flagellar systems, i.e., the sheathed polar flagellum (Pof) and numerous lateral flagella (Laf), both of which are strictly regulated by numerous factors. QsvR is an AraC-type regulator that controls biofilm formation and virulence of V. parahaemolyticus. In the present study, we showed that deletion of qsvR significantly enhanced swimming motility of V. parahaemolyticus, while the swarming motility was not affected by QsvR. QsvR bound to the regulatory DNA regions of flgAMN and flgMN within the Pof gene loci to repress their transcription, whereas it negatively controls the transcription of flgBCDEFGHIJ and flgKL-flaC in an indirect manner. However, over-produced QsvR was also likely to possess the binding activity to the regulatory DNA regions of flgBCDEFGHIJ and flgKL-flaC in a heterologous host. In summary, this work demonstrated that QsvR negatively regulated the swimming motility of V. parahaemolyticus via directly action on the transcription of Pof genes.

Biological and transcriptional studies reveal VmeL is involved in motility, biofilm formation and virulence in Vibrio parahaemolyticus

Vibrio parahaemolyticus is a marine pathogen thought to be the leading cause of seafood-borne gastroenteritis globally, urgently requiring efficient management methods. V. parahaemolyticus encodes 12 resistance/nodulation/division (RND) efflux systems. However, research on these systems is still in its infancy. In this study, we discovered that the inactivation of VmeL, a membrane fusion protein within the RND efflux systems, led to reduction of the ability of biofilm formation. Further results displayed that the decreased capacity of Congo red binding and the colony of ΔvmeL is more translucent compared with wild type strains, suggested reduced biofilm formation due to decreased production of biofilm exopolysaccharide upon vmeL deletion. In addition, the deletion of vmeL abolished surface swarming and swimming motility of V. parahaemolyticus. Additionally, deletion of vmeL weakened the cytotoxicity of V. parahaemolyticus towards HeLa cells, and impaired its virulence in a murine intraperitoneal infection assay. Finally, through RNA-sequencing, we ascertained that there were 716 upregulated genes and 247 downregulated genes in ΔvmeL strain. KEGG enrichment analysis revealed that quorum sensing, bacterial secretion systems, ATP-binding cassette transporters, and various amino acid metabolism pathways were altered due to the inactivation of vmeL. qRT-PCR further confirmed that genes accountable to the type III secretion system (T3SS1) and lateral flagella were negatively affected by vmeL deletion. Taken together, our results suggest that VmeL plays an important role in pathogenicity, making it a good target for managing infection with V. parahaemolyticus.