Role of VcrD1 protein in expression and secretion of flagellar components 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.

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.

Targeted phytogenic compounds against Vibrio parahaemolyticus biofilms

As one of main culprit of seafood-associated human illness, Vibrio parahaemolyticus can readily accumulate on biotic or abiotic surfaces to form biofilms in the seafood processing environment. Biofilm formation on various surfaces can provide a protective barrier for viable bacterial cells that are resistant to most traditional bacteriostatic measures. This underscores the necessity and urgency of developing effective alternative strategies to control V. parahaemolyticus biofilms. Plants have always provided an extensive and infinite source of biologically active compounds for "green" antibiofilm agents. This review summarizes recent developments in promising multitargeted phytogenic compounds against V. parahaemolyticus biofilms. This review provides valuable insights into potential research targets that can be pursued further to identify potent natural antibiofilm agents in the food industry.

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.

The quorum sensing regulator OpaR is a repressor of polar flagellum genes in Vibrio parahaemolyticus

Vibrio parahaemolyticus possesses two types of flagella: a single polar flagellum (Pof) for swimming and the peritrichous lateral flagella (Laf) for swarming. Expression of Laf genes has previously been reported to be regulated by the quorum sensing (QS) regulators AphA and OpaR. In the present study, we showed that OpaR, the QS regulator at high cell density (HCD), acted as a negative regulator of swimming motility and the transcription of Pof genes in V. parahaemolyticus. OpaR bound to the promoter-proximal DNA regions of flgAMN, flgMN, and flgBCDEFGHIJ within the Pof gene loci to repress their transcription, whereas it negatively regulates the transcription of flgKL-flaC in an indirect manner. Thus, this work investigated how QS regulated the swimming motility via direct action of its master regulator OpaR on the transcription of Pof genes in V. parahaemolyticus.

Motility of Vibrio spp.: regulation and controlling strategies

Flagellar motility in bacteria is a highly regulated and complex cellular process that requires high energy investment for movement and host colonization. Motility plays an important role in the lifestyle of Vibrio spp. in the aquatic environment and during host colonization. Flagellar motility in vibrios is associated with several cellular processes, such as movement, colonization, adhesion, biofilm formation, and virulence. The transcription of all flagella-related genes occurs hierarchically and is regulated positively or negatively by several transcription factors and regulatory proteins. The flagellar regulatory hierarchy is well studied in Vibrio cholerae and Vibrio parahaemolyticus. Here, we compared the regulatory cascade and molecules involved in the flagellar motility of V. cholerae and V. parahaemolyticus in detail. The evolutionary relatedness of the master regulator of the polar and lateral flagella in different Vibrio species is also discussed. Although they can form symbiotic associations of some Vibrio species with humans and aquatic organisms can be harmed by several species of Vibrio as a result of surface contact, characterized by flagellar movement. Thus, targeting flagellar motility in pathogenic Vibrio species is considered a promising approach to control Vibrio infections. This approach, along with the strategies for controlling flagellar motility in different species of Vibrio using naturally derived and chemically synthesized compounds, is discussed in this review. KEY POINTS: • Vibrio species are ubiquitous and distributed across the aquatic environments. • The flagellar motility is responsible for the chemotactic movement and initial colonization to the host. • The transition from the motile into the biofilm stage is one of the crucial events in the infection. • Several signaling pathways are involved in the motility and formation of biofilm. • Attenuation of motility by naturally derived or chemically synthesized compounds could be a potential treatment for preventing Vibrio biofilm-associated infections.

Stress Response of Vibrio parahaemolyticus and Listeria monocytogenes Biofilms to Different Modified Atmospheres

The sessile biofilms of Vibrio parahaemolyticus and Listeria monocytogenes have increasingly become a critical threat in seafood safety. This study aimed to evaluate the effects of modified atmospheres on the formation ability of V. parahaemolyticus and L. monocytogenes biofilms. The stress responses of bacterial biofilm formation to modified atmospheres including anaerobiosis (20% carbon dioxide, 80% nitrogen), micro-aerobiosis (20% oxygen, 80% nitrogen), and aerobiosis (60% oxygen, 40% nitrogen) were illuminated by determining the live cells, chemical composition analysis, textural parameter changes, expression of regulatory genes, etc. Results showed that the biofilm formation ability of V. parahaemolyticus was efficiently decreased, supported by the fact that the modified atmospheres significantly reduced the key chemical composition [extracellular DNA (eDNA) and extracellular proteins] of the extracellular polymeric substance (EPS) and negatively altered the textural parameters (biovolume, thickness, and bio-roughness) of biofilms during the physiological conversion from anaerobiosis to aerobiosis, while the modified atmosphere treatment increased the key chemical composition of EPS and the textural parameters of L. monocytogenes biofilms from anaerobiosis to aerobiosis. Meanwhile, the expression of biofilm formation genes (luxS, aphA, mshA, oxyR, and opaR), EPS production genes (cpsA, cpsC, and cpsR), and virulence genes (vopS, vopD1, vcrD1, vopP2β, and vcrD2β) of V. parahaemolyticus was downregulated. For the L. monocytogenes cells, the expression of biofilm formation genes (flgA, flgU, and degU), EPS production genes (Imo2554, Imo2504, inlA, rmlB), and virulence genes (vopS, vopD1, vcrD1, vopP2β, and vcrD2β) was upregulated during the physiological conversion. All these results indicated that the modified atmospheres possessed significantly different regulation on the biofilm formation of Gram-negative V. parahaemolyticus and Gram-positive L. monocytogenes, which will provide a novel insight to unlock the efficient control of Gram-negative and Gram-positive bacteria in modified-atmosphere packaged food.