Transcriptomic Analysis of Vibrio parahaemolyticus Underlying the Wrinkly and Smooth Phenotypes

Polyvinyl chloride microplastics facilitated the transmission of Vibrio parahaemolyticus from surrounding water to Litopenaeus vannamei

Microplastics (MPs) pose a major threat to marine life and ecosystems. However, the toxicological effects of MPs on crustaceans which are highly susceptible to MPs pollution are not fully understood. In addition, MPs can serve as the medium for pathogens, increasing the risk of disease outbreaks in shrimp aquaculture. To study the biological risks of MPs close to the aquacultural practice, the current study firstly focused on the impacts of MPs colonized by the pathogen Vibrio parahaemolyticus on shrimp Litopenaeus vannamei. The role of microplastics in facilitating pathogens infection of shrimps was firstly reported. Under this impact, the hepatopancreas of L. vannamei suffered severe damage. At 96 hpi, the shrimp mortality rate reached 100%. Dominant phyla altered in the intestinal and hepatopancreatic microbiota of L. vannamei. The characterization of the L. vannamei microbiota under the condition where the pathogens and MPs exist in the surroundings, to be used as a reference for comparison with healthy and diseased shrimp in the aquacultural system, is necessary.

Role of the TPR family protein VPA1365 in regulating type III secretion system 2 and virulence in Vibrio parahaemolyticus

Vibrio parahaemolyticus is a notable seafood-borne pathogen capable of colonizing the intestines of hosts and inducing acute gastroenteritis. The intestinal colonization and enterotoxicity of V. parahaemolyticus are highly reliant on the type III secretion system 2 (T3SS2), encoded within the pathogenicity island (Vp-PAI). The expression of Vp-PAI is strictly regulated by bile acid signals and transcriptional regulators VtrA/VtrB. In this study, we identified a tetratricopeptide repeat (TPR) family protein named VPA1365, which regulates the expression of T3SS2 and is indispensable for the intestinal colonization of V. parahaemolyticus. The expression and secretion of the T3SS2-dependent protein VopD2 were significantly reduced in Δvpa1365 compared to that of the wild type (WT), suggesting that VPA1365 positively regulates the function of T3SS2. Further research indicated that VPA1365 directly binds to the promoters of vtrA, thereby increasing the expression levels of T3SS2-associated genes. Additionally, the deletion of vpa1365 markedly reduced the cytotoxicity, adhesion ability, biofilm formation, and hemolytic activity of V. parahaemolyticus. VPA1365 was found to control the expression levels of these virulence-associated genes by binding to the promoters of scrG, pilA, and mshA. In a zebrafish infection model, the Δvpa1365 infected groups demonstrated a higher survival rate compared to the zebrafish infected with WT. In conclusion, this study identified a TPR family protein VPA1365, which regulates the expression levels of T3SS2 and virulence-associated genes in V. parahaemolyticus, further broadening our understanding of its virulence factors.

IMPORTANCE

The type III secretion system 2 (T3SS2) is of crucial significance for the pathogenicity of Vibrio parahaemolyticus; nevertheless, the biological functions of many genes within the T3SS2 gene cluster and the transcriptional regulatory network of T3SS2 remain ambiguous. In this study, we identified VPA1365, a tetratricopeptide repeat family regulator encoded in the T3SS2 gene cluster, which differs from other known T3SS2 regulatory factors, such as OmpR, ToxR, or LysR family proteins. VPA1365 not only positively regulated the expression and secretion of T3SS2-related proteins but also enhanced the virulence in infant rabbits and zebrafish. Moreover, we identified several novel functions of VPA1365, such as its contribution to hemolytic activity, biofilm formation, cytotoxicity, and adhesion ability, uncovering its global physiological role in V. parahaemolyticus. The putative VPA1365-binding site was predicted and identified through the MEME-Suite tool and electrophoretic mobility shift analysis. Collectively, these results broaden our understanding of the regulatory pathways of T3SS2 and virulence.

GepA, a GGDEF-EAL protein, regulates biofilm formation and swimming motility in Vibrio parahaemolyticus

Cyclic diguanylate monophosphate (c-di-GMP) is a second messenger that regulates multiple bacterial behaviors. It is synthesized by diguanylate cyclase (DGC) with the GGDEF domain, and degraded by phosphodiesterase (PDE) with the EAL or HD-GYP domain. The GepA (VP0117) protein in Vibrio parahaemolyticus contains both GGDEF and EAL domains, but its role remains unknown. This study found that deletion of the EAL domain or both the GGDEF and EAL domains in GepA increased intracellular c-di-GMP levels, enhanced biofilm formation, and inhibited polar flagellum-mediated swimming motility. Deletion of only the GGDEF domain had no such effects. Additionally, removing the EAL domain or both the GGDEF and EAL domains increased cpsA expression and decreased polar flagellar gene expression, while deleting the GGDEF domain alone had no impact on these genes. Overexpression of GepA or a GepA variant with a mutated GGDEF domain reduced biofilm formation but increased swimming motility. However, overexpression of GepA with a mutated EAL domain did not produce the expected phenotypic changes. In summary, GepA functions as a PDE to degrade c-di-GMP, thereby suppressing biofilm formation and enhancing swimming motility in V. parahaemolyticus.

GefB, a GGDEF domain-containing protein, affects motility and biofilm formation of Vibrio parahaemolyticus and is regulated by quorum sensing regulators

Vibrio parahaemolyticus (V. parahaemolyticus) stands as the predominant etiological agent responsible for gastroenteritis associated with the consumption of seafood. Cyclic di-guanosine monophosphate (c-di-GMP), a secondary messenger in bacteria, controls multiple bacterial behaviors including pathogenesis, the development of biofilms, and motility. The protein GefB (VPA1478), characterized by the presence of a GGDEF domain, inhibits the swarming motility of V. parahaemolyticus. In this study, we showed that deletion of gefB remarkably reduced cellular c-di-GMP level and biofilm formation by V. parahaemolyticus, but significantly enhanced the swimming and swarming motility. In addition, GefB inhibited the polar and lateral flagellar genes but activated genes associated with exopolysaccharide production of V. parahaemolyticus. The data also demonstrated that vpa1477 and gefB are co-transcribed as a single transcriptional unit, designated as vpa1477-gefB. Transcription of vpa1477-gefB was under the collective regulation of the master quorum sensing (QS) regulators AphA and OpaR, which function at low (LCD) and high cell density (HCD), respectively. AphA positively regulated vpa1477-gefB transcription at LCD, whereas OpaR negatively regulated its transcription at HCD. The findings significantly enhance our comprehension of the metabolism and regulatory mechanisms of c-di-GMP in V. 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.

VPA0198, a GGDEF domain-containing protein, affects the motility and biofilm formation of Vibrio parahaemolyticus and is regulated by quorum sensing associated regulators

Cyclic di-GMP (c-di-GMP), a ubiquitous secondary messenger in bacteria, affects multiple bacterial behaviors including motility and biofilm formation. c-di-GMP is synthesized by diguanylate cyclase harboring a GGDEF domain and degraded by phosphodiesterase harboring an either EAL or HD-GYP domain. Vibrio parahaemolyticus, the leading cause of seafood-associated gastroenteritis, harbors more than 60 genes involved in c-di-GMP metabolism. However, roles of most of these genes including vpa0198, which encodes a GGDEF-domain containing protein, are still completely unknown. AphA and OpaR are the master quorum sensing (QS) regulators operating at low (LCD) and high cell density (HCD), respectively. QsvR integrates into QS to control gene expression via direct regulation of AphA and OpaR. In this study, we showed that deletion of vpa0198 remarkably reduced c-di-GMP production and biofilm formation, whereas promoted the swimming motility of V. parahaemolyticus. Overexpression of VPA0198 in the vpa0198 mutant strain significantly reduced the swimming and swarming motility and enhanced the biofilm formation ability of V. parahaemolyticus. In addition, transcription of vpa0198 was under the collective regulation of AphA, OpaR and QsvR. AphA activated the transcription of vpa0198 at LCD, whereas QsvR and OpaR coordinately and directly repressed vpa0198 transcription at HCD, thereby leading to a cell density-dependent expression of vpa0198. Therefore, this work expanded the knowledge of synthetic regulatory mechanism of c-di-GMP in V. parahaemolyticus.

Virulence phenotypes differ between toxigenic Vibrio parahaemolyticus isolated from western coasts of Europe

Vibrio parahaemolyticus is the leading bacterial cause of gastroenteritis associated with seafood consumption worldwide. Not all members of the species are thought to be pathogenic, thus identification of virulent organisms is essential to protect public health and the seafood industry. Correlations of human disease and known genetic markers (e.g. thermostable direct hemolysin (TDH), TDH-related hemolysin (TRH)) appear complex. Some isolates recovered from patients lack these factors, while their presence has become increasingly noted in isolates recovered from the environment. Here, we used whole-genome sequencing in combination with mammalian and insect models of infection to assess the pathogenic potential of V. parahaemolyticus isolated from European Atlantic shellfish production areas. We found environmental V. parahaemolyticus isolates harboured multiple virulence-associated genes, including TDH and/or TRH. However, carriage of these factors did not necessarily reflect virulence in the mammalian intestine, as an isolate containing TDH and the genes coding for a type 3 secretion system (T3SS) 2α virulence determinant, appeared avirulent. Moreover, environmental V. parahaemolyticus lacking TDH or TRH could be assigned to groups causing low and high levels of mortality in insect larvae, with experiments using defined bacterial mutants showing that a functional T3SS1 contributed to larval death. When taken together, our findings highlight the genetic diversity of V. parahaemolyticus isolates found in the environment, their potential to cause disease and the need for a more systematic evaluation of virulence in diverse V. parahaemolyticus to allow better genetic markers.

Effect of capsular polysaccharide phase variation on biofilm formation, motility and gene expression in Vibrio vulnificus

Vibrio vulnificus, a significant marine pathogen, undergoes opaque (Op)-translucent (Tr) colony switching based on whether capsular polysaccharide (CPS) is produced. CPS phase variation is sometime accompanied by genetic variation or down-regulation of particular genes, such as wzb. In addition, CPS prevents biofilm formation and is important to the virulence of V. vulnificus. However, the extent to which there is a difference in gene expression between Tr and Op colonies and the impact of CPS phase variation on other behaviors of V. vulnificus remain unknown. In this work, the data have shown that CPS phase variation of V. vulnificus is affected by incubation time. Tr and Op strains exhibited similar growth rates. However, Tr strains had enhanced biofilm formation capacities but reduced swimming motility compared to Op strains. The RNA-seq assay revealed 488 differentially expressed genes, with 214 downregulated and 274 upregulated genes, between Tr and Op colonies. Genes associated with Tad pili and CPS were downregulated, whereas those involved in flagellum were upregulated, in Tr colonies compared with Op colonies. In addition, 9 putative c-di-GMP metabolism-associated genes and 28 genes encoding putative regulators were significantly differentially expressed, suggesting that CPS phase variation is probably strictly regulated in V. vulnificus. Moreover, 8 genes encoding putative porins were also differentially expressed between the two phenotypic colonies, indicating that bacterial outer membrane was remodeled during CPS phase variation. In brief, this work highlighted the gene expression profiles associated with CPS phase variation, but more studies should be performed to disclose the intrinsic mechanisms in the future.

IcmF2 of the type VI secretion system 2 plays a role in biofilm formation of Vibrio parahaemolyticus

Vibrio parahaemolyticus possesses two distinct type VI secretion systems (T6SS), namely T6SS1 and T6SS2. T6SS1 is predominantly responsible for adhesion to Caco-2 and HeLa cells and for the antibacterial activity of V. parahaemolyticus, while T6SS2 mainly contributes to HeLa cell adhesion. However, it remains unclear whether the T6SS systems have other physiological roles in V. parahaemolyticus. In this study, we demonstrated that the deletion of icmF2, a structural gene of T6SS2, reduced the biofilm formation capacity of V. parahaemolyticus under low salt conditions, which was also influenced by the incubation time. Nonetheless, the deletion of icmF2 did not affect the biofilm formation capacity in marine-like growth conditions, nor did it impact the flagella-driven swimming and swarming motility of V. parahaemolyticus. IcmF2 was found to promote the production of the main components of the biofilm matrix, including extracellular DNA (eDNA) and extracellular proteins, and cyclic di-GMP (c-di-GMP) in V. parahaemolyticus. Additionally, IcmF2 positively influenced the transcription of cpsA, mfpA, and several genes involved in c-di-GMP metabolism, including scrJ, scrL, vopY, tpdA, gefA, and scrG. Conversely, the transcription of scrA was negatively impacted by IcmF2. Therefore, IcmF2-dependent biofilm formation was mediated through its effects on the production of eDNA, extracellular proteins, and c-di-GMP, as well as its impact on the transcription of cpsA, mfpA, and genes associated with c-di-GMP metabolism. This study confirmed new physiological roles for IcmF2 in promoting biofilm formation and c-di-GMP production in V. parahaemolyticus.

Environmental magnesium ion affects global gene expression, motility, biofilm formation and virulence of Vibrio parahaemolyticus

Vibrio parahaemolyticus is widely distributed in marine ecosystems. Magnesium ion (Mg2+) is the second most abundant metal cation in seawater, and plays important roles in the growth and gene expression of V. parahaemolyticus, but lacks the detailed mechanisms. In this study, the RNA sequencing data demonstrated that a total of 1494 genes was significantly regulated by Mg2+. The majority of the genes associated with lateral flagella, exopolysaccharide, type III secretion system 2, type VI secretion system (T6SS) 1, T6SS2, and thermostable direct hemolysin were downregulated. A total of 18 genes that may be involved in c-di-GMP metabolism and more than 80 genes encoding putative regulators were also significantly and differentially expressed in response to Mg2+, indicating that the adaptation process to Mg2+ stress may be strictly regulated by complex regulatory networks. In addition, Mg2+ promoted the proliferative speed, swimming motility and cell adhesion of V. parahaemolyticus, but inhibited the swarming motility, biofilm formation, and c-di-GMP production. However, Mg2+ had no effect on the production of capsular polysaccharide and cytoxicity against HeLa cells. Therefore, Mg2+ had a comprehensive impact on the physiology and gene expression of V. parahaemolyticus.

The effect of environmental calcium on gene expression, biofilm formation and virulence of Vibrio parahaemolyticus

Calcium (Ca2+) can regulate the swarming motility and virulence of Vibrio parahaemolyticus BB22. However, the effects of Ca2+ on the physiology of V. parahaemolyticus RIMD2210633, whose genomic composition is quite different with that of BB22, have not been investigated. In this study, the results of phenotypic assays showed that the biofilm formation, c-di-GMP production, swimming motility, zebrafish survival rate, cytoxicity against HeLa cells, and adherence activity to HeLa cells of V. parahaemolyticus RIMD2210633 were significantly enhanced by Ca2+. However, Ca2+ had no effect on the growth, swarming motility, capsular polysaccharide (CPS) phase variation and hemolytic activity. The RNA sequencing (RNA-seq) assay disclosed 459 significantly differentially expressed genes (DEGs) in response to Ca2+, including biofilm formation-associated genes and those encode virulence factors and putative regulators. DEGs involved in polar flagellum and T3SS1 were upregulated, whereas majority of those involved in regulatory functions and c-di-GMP metabolism were downregulated. The work helps us understand how Ca2+ affects the behavior and gene expression of V. parahaemolyticus RIMD2210633.

QsvR and OpaR coordinately regulate the transcription of cpsS and cpsR in Vibrio parahaemolyticus

Vibrio parahaemolyticus, the leading cause of seafood-associated gastroenteritis, has a strong capacity to form biofilms on surfaces, which is strictly regulated by the CpsS-CpsR-CpsQ regulatory cascade. OpaR, a master regulator of quorum sensing, is a global regulator that controls multiple cellular pathways including biofilm formation and virulence. QsvR is an AraC-type regulator that works coordinately with OpaR to control biofilm formation and virulence gene expression of V. parahaemolyticus. QsvR and OpaR activate cpsQ transcription. OpaR also activates cpsR transcription, but lacks the detailed regulatory mechanisms. Furthermore, it is still unknown whether QsvR regulates cpsR transcription, as well as whether QsvR and OpaR regulate cpsS transcription. In this study, the results of quantitative real-time PCR and LacZ fusion assays demonstrated that deletion of qsvR and/or opaR significantly decreased the expression levels of cpsS and cpsR compared to the wild-type strain. However, the results of two-plasmid lacZ reporter and electrophoretic mobility-shift assays showed that both QsvR and OpaR were unable to bind the regulatory DNA regions of cpsS and cpsR. Therefore, transcription of cpsS and cpsR was coordinately and indirectly activated by QsvR and OpaR. This work enriched our knowledge on the regulatory network of biofilm formation in V. parahaemolyticus.

Molecular Aspects of the Functioning of Pathogenic Bacteria Biofilm Based on Quorum Sensing (QS) Signal-Response System and Innovative Non-Antibiotic Strategies for Their Elimination

One of the key mechanisms enabling bacterial cells to create biofilms and regulate crucial life functions in a global and highly synchronized way is a bacterial communication system called quorum sensing (QS). QS is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small signalling molecules called autoinducers (AIs). In bacteria, QS controls the biofilm formation through the global regulation of gene expression involved in the extracellular polymeric matrix (EPS) synthesis, virulence factor production, stress tolerance and metabolic adaptation. Forming biofilm is one of the crucial mechanisms of bacterial antimicrobial resistance (AMR). A common feature of human pathogens is the ability to form biofilm, which poses a serious medical issue due to their high susceptibility to traditional antibiotics. Because QS is associated with virulence and biofilm formation, there is a belief that inhibition of QS activity called quorum quenching (QQ) may provide alternative therapeutic methods for treating microbial infections. This review summarises recent progress in biofilm research, focusing on the mechanisms by which biofilms, especially those formed by pathogenic bacteria, become resistant to antibiotic treatment. Subsequently, a potential alternative approach to QS inhibition highlighting innovative non-antibiotic strategies to control AMR and biofilm formation of pathogenic bacteria has been discussed.

The phase variation between wrinkly and smooth colony phenotype affects the virulence of Vibrio parahaemolyticus

Vibrio parahaemolyticus, the causative agent of seafood-associated gastroenteritis, undergoes wrinkly and smooth colony switching on the plate. The wrinkly spreader grew faster, had stronger motility and biofilm capacity when compared with the smooth one. However, whether the two phenotypes differ in their virulence still needs to be further investigated. In this study, the data showed that the smooth spreader had stronger virulence phenotypes, including the cytotoxicity against HeLa cells, antibacterial activity against E. coli, adhesive capacity toward HeLa cells, and lethality in zebrafish, relative to the wrinkly one. However, the colony morphology variation had no influence on the haemolytic activity. The mRNA levels of major virulence genes including T3SS1, T6SS1, and T6SS2 were significantly enhanced in the smooth colonies relative to those in the wrinkly colonies. Taken together, the presented work highlighted the different virulence profiles of the wrinkly and smooth colony phenotypes.

L-arabinose affects the growth, biofilm formation, motility, c-di-GMP metabolism, and global gene expression of Vibrio parahaemolyticus

The L-arabinose inducible pBAD vectors are commonly used to turn on and off the expression of specific genes in bacteria. The utilization of certain carbohydrates can influence bacterial growth, virulence factor production, and biofilm formation. Vibrio parahaemolyticus, the causative agent of seafood-associated gastroenteritis, can grow in media with L-arabinose as the sole carbon source. However, the effects of L-arabinose on V. parahaemolyticus physiology have not been investigated. In this study, we show that the growth rate, biofilm formation capacity, capsular polysaccharide production, motility, and c-di-GMP production of V. parahaemolyticus are negatively affected by L-arabinose. RNA-seq data revealed significant changes in the expression levels of 752 genes, accounting for approximately 15.6% of V. parahaemolyticus genes in the presence of L-arabinose. The affected genes included those associated with L-arabinose utilization, major virulence genes, known key biofilm-related genes, and numerous regulatory genes. In the majority of type III secretion system, two genes were upregulated in the presence of L-arabinose, whereas in those of type VI secretion system, two genes were downregulated. Ten putative c-di-GMP metabolism-associated genes were also significantly differentially expressed, which may account for the reduced c-di-GMP levels in the presence of L-arabinose. Most importantly, almost 40 putative regulators were significantly differentially expressed due to the induction by L-arabinose, indicating that the utilization of L-arabinose is strictly regulated by regulatory networks in V. parahaemolyticus. The findings increase the understanding of how L-arabinose affects the physiology of V. parahaemolyticus. Researchers should use caution when considering the use of L-arabinose inducible pBAD vectors in V. parahaemolyticus. IMPORTANCE The data in this study show that L-arabinose negatively affects the growth rate, biofilm formation, capsular polysaccharide production, motility, and c-di-GMP production of V. parahaemolyticus. The data also clarify the gene expression profiles of the bacterium in the presence of L-arabinose. Significantly differentially expressed genes in response to L-arabinose were involved in multiple cellular pathways, including L-arabinose utilization, virulence factor production, biofilm formation, motility, adaptation, and regulation. The collective findings indicate the significant impact of L-arabinose on the physiology of V. parahaemolyticus. There may be similar effects on other species of bacteria. Necessary controls should be established when pBAD vectors must be used for ectopic gene expression.

Effect of sublethal dose of chloramphenicol on biofilm formation and virulence in Vibrio parahaemolyticus

Vibrio parahaemolyticus isolates are generally very sensitive to chloramphenicol. However, it is usually necessary to transfer a plasmid carrying a chloramphenicol resistance gene into V. parahaemolyticus to investigate the function of a specific gene, and the effects of chloramphenicol on bacterial physiology have not been investigated. In this work, the effects of sublethal dose of chloramphenicol on V. parahaemolyticus were investigated by combined utilization of various phenotypic assays and RNA sequencing (RNA-seq). The results showed that the growth rate, biofilm formation capcity, c-di-GMP synthesis, motility, cytoxicity and adherence activity of V. parahaemolyticus were remarkably downregulated by the sublethal dose of chloramphenicol. The RNA-seq data revealed that the expression levels of 650 genes were significantly differentially expressed in the response to chloramphenicol stress, including antibiotic resistance genes, major virulence genes, biofilm-associated genes and putative regulatory genes. Majority of genes involved in the synthesis of polar flagellum, exopolysaccharide (EPS), mannose-sensitive haemagglutinin type IV pilus (MSHA), type III secretion systems (T3SS1 and T3SS2) and type VI secretion system 2 (T6SS2) were downregulated by the sublethal dose of chloramphenicol. Five putative c-di-GMP metabolism genes were significantly differentially expressed, which may be the reason for the decrease in intracellular c-di-GMP levels in the response of chloramphenicol stress. In addition, 23 genes encoding putative regulators were also significantly differentially expressed, suggesting that these regulators may be involved in the resistance of V. parahaemolyticus to chloramphenicol stress. This work helps us to understand how chloramphenicol effect on the physiology of V. parahaemolyticus.

Quorum sensing signal synthases enhance Vibrio parahaemolyticus swarming motility

Vibrio parahaemolyticus is a significant food-borne pathogen that is found in diverse aquatic habitats. Quorum sensing (QS), a signaling system for cell-cell communication, plays an important role in V. parahaemolyticus persistence. We characterized the function of three V. parahaemolyticus QS signal synthases, CqsAvp , LuxMvp , and LuxSvp , and show that they are essential to activate QS and regulate swarming. We found that CqsAvp , LuxMvp , and LuxSvp activate a QS bioluminescence reporter through OpaR. However, V. parahaemolyticus exhibits swarming defects in the absence of CqsAvp , LuxMvp , and LuxSvp , but not OpaR. The swarming defect of this synthase mutant (termed Δ3AI) was recovered by overexpressing either LuxOvp D47A , a mimic of dephosphorylated LuxOvp mutant, or the scrABC operon. CqsAvp , LuxMvp , and LuxSvp inhibit lateral flagellar (laf) gene expression by inhibiting the phosphorylation of LuxOvp and the expression of scrABC. Phosphorylated LuxOvp enhances laf gene expression in a mechanism that involves modulating c-di-GMP levels. However, enhancing swarming requires phosphorylated and dephosphorylated LuxOvp which is regulated by the QS signals that are synthesized by CqsAvp , LuxMvp , and LuxSvp . The data presented here suggest an important strategy of swarming regulation by the integration of QS and c-di-GMP signaling pathways in V. parahaemolyticus.