Identification of proteins secreted via Vibrio parahaemolyticus type III secretion system 1

Vibrio alginolyticus Reprograms CIK Cell Metabolism via T3SS Effector VopS to Promote Host Cell Ferroptosis

Vibrio alginolyticus is a Gram-negative pathogen of both marine animals and humans, resulting in significant losses for the aquaculture industry. Emerging evidence indicates that V. alginolyticus manipulates cell death for its pathogenicity, but the underlying molecular mechanisms remain unclear. Here, a gene designated vopS in V. alginolyticus HY9901 was identified, which was predicted to encode the T3SS effector protein. To determine whether VopS contributes to the pathogenesis of V. alginolyticus, the ΔvopS mutant strain was constructed and phenotypically characterized. The deletion of VopS not only reduced the ability to secrete extracellular proteases and virulence but also affected the expression of the T3SS genes. Furthermore, VopS was cytotoxic and induced apoptosis, as confirmed by elevated LDH and the activation of caspase-3. Metabolomic analysis revealed considerable metabolomic disruptions upon V. alginolyticus infection. The VopS effector induced host cell ferroptosis by promoting the synthesis of adrenic acid, depleting cellular glutathione, and subsequently increasing the accumulation of ferrous (Fe2+). Taken together, our findings provide that the VopS effector is an essential virulence factor of V. alginolyticus, which can lead to ferroptosis.

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.

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.

Genetic Insights into Biofilm Formation by a Pathogenic Strain of Vibrio harveyi

The Vibrio genus includes bacteria widely distributed in aquatic habitats and the infections caused by these bacteria can affect a wide range of hosts. They are able to adhere to numerous surfaces, which can result in biofilm formation that helps maintain them in the environment. The involvement of the biofilm lifestyle in the virulence of Vibrio pathogens of aquatic organisms remains to be investigated. Vibrio harveyi ORM4 is a pathogen responsible for an outbreak in European abalone Haliotis tuberculata populations. In the present study, we used a dynamic biofilm culture technique coupled with laser scanning microscopy to characterize the biofilm formed by V. harveyi ORM4. We furthermore used RNA-seq analysis to examine the global changes in gene expression in biofilm cells compared to planktonic bacteria, and to identify biofilm- and virulence-related genes showing altered expression. A total of 1565 genes were differentially expressed, including genes associated with motility, polysaccharide synthesis, and quorum sensing. The up-regulation of 18 genes associated with the synthesis of the type III secretion system suggests that this virulence factor is induced in V. harveyi ORM4 biofilms, providing indirect evidence of a relationship between biofilm and virulence.

Expression regulation of type III secretion system 2 in Vibrio parahaemolyticus by catabolite activator protein

Vibrio parahaemolyticus has two sets of type III secretion systems that are major pathogenic factors: T3SS1 (cytotoxicity) and T3SS2 (enterotoxicity). V. parahaemolyticus mainly colonizes the distal small intestine after oral infection and may be exposed to carbon-limiting stress due to the lack of readily available carbohydrates in this environment. Catabolite activator protein (CAP), a transcription factor involved in carbon-limiting metabolism in many Gram-negative bacteria, is well known to be involved in the regulation of the expression of many virulence factors. In this study, we determined the effects of CAP on the expression of T3SSs in this bacterium. Based on a lactate dehydrogenase-based cytotoxicity assay, CAP was found to have a greater contribution to the expression of T3SS2-dependent cytotoxicity than to that of T3SS1. Reverse transcription quantitative PCR revealed decreased expression of many T3SS2-related genes, including vpa1348, in the cap gene deletion mutant compared to the parent strain. CAP was demonstrated to bind near the T-rich elements within the vpa1348 promoter region in an electrophoretic mobility shift assay and DNase I footprinting. CAP also enhanced the expression of vpa1348 in a β-galactosidase reporter assay. Collectively, these results suggest that CAP is involved in T3SS2-mediated virulence by regulating the expression of vpa1348 in V. parahaemolyticus.

ArcB orchestrates the quorum-sensing system to regulate type III secretion system 1 in Vibrio parahaemolyticus

In many Vibrio species, virulence is regulated by quorum sensing, which is regulated by a complex, multichannel, two-component phosphorelay circuit. Through this circuit, sensor kinases transmit sensory information to the phosphotransferase LuxU via a phosphotransfer mechanism, which in turn transmits the signal to the response regulator LuxO. For Vibrio parahaemolyticus, type III secretion system 1 (T3SS1) is required for cytotoxicity, but it is unclear how quorum sensing regulates T3SS1 expression. Herein, we report that a hybrid histidine kinase, ArcB, instead of LuxU, and sensor kinase LuxQ and response regulator LuxO, collectively orchestrate T3SS1 expression in V. parahaemolyticus. Under high oxygen conditions, LuxQ can interact with ArcB directly and phosphorylates the Hpt domain of ArcB. The Hpt domain of ArcB phosphorylates the downstream response regulator LuxO instead of ArcA. LuxO then activates transcription of the T3SS1 gene cluster. Under hypoxic conditions, ArcB autophosphorylates and phosphorylates ArcA, whereas ArcA does not participate in regulating the expression of T3SS1. Our data provides evidence of an alternative regulatory path involving the quorum sensing phosphorelay and adds another layer of understanding about the environmental regulation of gene expression in V. parahaemolyticus.

Non-clinical isolates of Vibrio parahaemolyticus harbouring traits of potential pathogenicity and fitness: A molecular analysis

Here we investigated the distribution of virulence and fitness attributes V. parahaemolyticus isolated from marine environment (n = 105). We discovered ∼1% of isolates positive for tdh, 8.57% for trh, and 4.76% had tdh and trh genes. More than 50% of the isolates had pathogenicity islands specific to pandemic clones and secretion systems which are detected partially or entirely. VPaI-1 found in 59.04%; VPaI-4 in 60%; VPaI-5 in 34.28%; VPaI-2 in 99.04%; VPaI-3 in 91.42% and VPaI-6 in 99.04% isolates. Also, 34.28% of the isolates harboured T3SS2 encoding VPaI 7; T3SS1 in 98.09%; T6SS2 in 99.04% isolates and T6SS1 in 60.95% isolates. The cytotoxicity analysis showed a significant effect by causing when infected with trh⁺ environmental isolates. The expression of the trh, VopC, and VopA genes during infection showed a significant upregulation. This suggests the presence of virulence traits among V. parahaemolyticus that could threaten public health.

The Missing Pieces: The Role of Secretion Systems in Campylobacter jejuni Virulence

Campylobacter jejuni is likely the most common bacterial cause of gastroenteritis worldwide, responsible for millions of cases of inflammatory diarrhea characterized by severe abdominal cramps and blood in the stool. Further, C. jejuni infections are associated with post-infection sequelae in developed countries and malnutrition and growth-stunting in low- and middle-income countries. Despite the increasing prevalence of the disease, campylobacteriosis, and the recognition that this pathogen is a serious health threat, our understanding of C. jejuni pathogenesis remains incomplete. In this review, we focus on the Campylobacter secretion systems proposed to contribute to host-cell interactions and survival in the host. Moreover, we have applied a genomics approach to defining the structural and mechanistic features of C. jejuni type III, IV, and VI secretion systems. Special attention is focused on the flagellar type III secretion system and the prediction of putative effectors, given that the proteins exported via this system are essential for host cell invasion and the inflammatory response. We conclude that C. jejuni does not possess a type IV secretion system and relies on the type III and type VI secretion systems to establish a niche and potentiate disease.

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.

VscF in T3SS1 Helps to Translocate VPA0226 in Vibrio parahaemolyticus

In Vibrio parahaemolyticus, type III secretion system 1 (T3SS1) is a major virulence factor that delivers effectors into the host eukaryotic cytoplasm; however, studies on its infection mechanism are currently limited. To determine the function of the vscF gene, we constructed the vscF deletion mutant ΔvscF and complementation strain CΔvscF. Compared with those of wild-type POR-1 and CΔvscF, the cytotoxic, adherent, and apoptotic abilities of ΔvscF in HeLa cells were significantly reduced (P < 0.01). Furthermore, in infected HeLa cells, the mutant strain reduced the translocation rates of VP1683 and VP1686 effectors compared to the wild-type and complementation strains. A BLAST search showed that vscF is homologous to the MixH needle protein of Shigella flexneri, indicating that the vscF gene encodes the needle protein of T3SS1 in V. parahaemolyticus. Additional translocation assays showed that VPA0226 translocated into the HeLa eukaryotic cytoplasm via T3SS1, secretion assays showed that VPA0226 can be secreted to supernatant by T3SS1, indicating that VPA0226 belongs to the unpublished class of T3SS1 effectors. In conclusion, our data indicate an essential role of vscF in V. parahaemolyticus T3SS1 and revealed that VPA0226 can be secreted into the host cell cytoplasm via T3SS1. This study provides insights into a previously unexplored aspect of T3SS1, which is expected to contribute to the understanding of its infection mechanism.

Analysis of Secreted Proteins and Potential Virulence via the ICEs-Mediated Pathway of the Foodborne Pathogen Vibrio parahaemolyticus

Vibrio parahaemolyticus uses bacterial secretion systems and integrative and conjugative elements (ICEs) to induce various diseases and to adapt to harsh environments, respectively. Information pertaining to the identity of secreted proteins and functional characterization of ICEs has been previously reported, but the relationship between these elements remains unclear. Herein we investigated secreted proteins of V. parahaemolyticus strains JHY20 and JHY20△ICE using two-dimensional gel electrophoresis and LC-MS/MS, which led to the identification of an ICE-associated secreted protein – dihydrolipoamide dehydrogenase (DLDH). Considering the data related to its physical and biochemical characterization, we predicted that DLDH is a novel immunogenic protein and associated with virulence in JHY20. Our findings indicate a potential relationship between ICE-associated transport and secreted proteins and shed light on the function of such transport mechanisms. We believe that our data should enhance our understanding of mobile genetic elements.

Manipulation of IRE1-Dependent MAPK Signaling by a Vibrio Agonist-Antagonist Effector Pair

Diverse bacterial pathogens employ effector delivery systems to disrupt vital cellular processes in the host (N. M. Alto and K. Orth, Cold Spring Harbor Perspect Biol 4:a006114, 2012, https://doi.org/10.1101/cshperspect.a006114). The type III secretion system 1 of the marine pathogen Vibrio parahaemolyticus utilizes the sequential action of four effectors to induce a rapid, proinflammatory cell death uniquely characterized by a prosurvival host transcriptional response (D. L. Burdette, M. L. Yarbrough, A Orvedahl, C. J. Gilpin, and K. Orth, Proc Natl Acad Sci USA 105:12497-12502, 2008, https://doi.org/10.1073/pnas.0802773105; N. J. De Nisco, M. Kanchwala, P. Li, J. Fernandez, C. Xing, and K. Orth, Sci Signal 10:eaa14501, 2017, https://doi.org/10.1126/scisignal.aal4501). Herein, we show that this prosurvival response is caused by the action of the channel-forming effector VopQ that targets the host V-ATPase, resulting in lysosomal deacidification and inhibition of lysosome-autophagosome fusion. Recent structural studies have shown how VopQ interacts with the V-ATPase and, while in the ER, a V-ATPase assembly intermediate can interact with VopQ, causing a disruption in membrane integrity. Additionally, we observed that VopQ-mediated disruption of the V-ATPase activates the IRE1 branch of the unfolded protein response (UPR), resulting in an IRE1-dependent activation of ERK1/2 MAPK signaling. We also find that this early VopQ-dependent induction of ERK1/2 phosphorylation is terminated by the VopS-mediated inhibitory AMPylation of Rho GTPase signaling. Since VopS dampens VopQ-induced IRE1-dependent ERK1/2 activation, we propose that IRE1 activates ERK1/2 phosphorylation at or above the level of Rho GTPases. This study illustrates how temporally induced effectors can work as in tandem as agonist/antagonist to manipulate host signaling and reveals new connections between V-ATPase function, UPR, and MAPK signaling.IMPORTANCE Vibrio parahaemolyticus is a seafood-borne pathogen that encodes two type 3 secretion systems (T3SS). The first system, T3SS1, is thought to be maintained in all strains of V. parahaemolyticus to maintain survival in the environment, whereas the second system, T3SS2, is linked to clinical isolates and disease in humans. Here, we found that first system targets evolutionarily conserved signaling systems to manipulate host cells, eventually causing a rapid, orchestrated cells death within 3 h. We have found that the T3SS1 injects virulence factors that temporally manipulate host signaling. Within the first hour of infection, the effector VopQ acts first by activating host survival signals while diminishing the host cell apoptotic machinery. Less than an hour later, another effector, VopS, reverses activation and inhibition of these signaling systems, ultimately leading to death of the host cell. This work provides example of how pathogens have evolved to manipulate the interplay between T3SS effectors to regulate host signaling pathways.

[Mechanisms of action of Vibrio parahaemoltyicus cytotoxins]

Vibrio parahaemolyticus, one of the Gram-negative common enteric pathogens, was first isolated in Japan in 1950. Since its discovery, this bacterium has been a major cause of food-poisoning in Japan, and its infection has recently undergone a global expansion. V. parahaemolyticus possesses a classical exotoxin, thermostable direct hemolysin, and two sets of type III secretion systems (T3SSs) that are able to inject effectors directly into host cells, which are its key virulence factors. Exotoxin/effector is exploited by many Gram-negative pathogens, and plays critical roles in pathogenesis by damaging host cells or by modulating host cell functions, through its activity on/in host cells. In recent years, functional activities of T3SS effectors produced by V. parahaemolyticus have been extensively studied, which has substantially increased our understanding of the pathogenic mechanisms of the bacterium. In paricular, some T3SS effectors of V. parahaemolyticus act as cytotoxins and thereby damage host cells. Here, I focus on these cytotoxic effectors of V. parahaemolyticus and describe recent advances in our understanding of their mechanisms of action.

Characterization of Vibrio parahaemolyticus strains isolated from clinically asymptomatic seafood workers

Vibrio parahaemolyticus (VP) is a major cause of gastroenteritis outbreaks in Thailand and other countries due to the consumption of contaminated and undercooked seafood. However, there have been few reports of the molecular epidemiology of VP isolates from asymptomatic seafood handlers. Here, we report the phenotypic and genetic characterization of 61 VP isolates obtained from asymptomatic workers in two seafood-processing plants. We found 24 O:K serotypes, of which O11:KUT, O1:KUT and O3:KUT were the dominant serotypes. Analysis by PCR showed that 12 isolates harbored either tdh or trh genes with the potential to be pathogenic VP strains. The presence of T3SS2α and T3SS2β genes was correlated with the presence of tdh and trh, respectively. Four tdh+ isolates were positive for pandemic marker. In this study, VP isolates were commonly resistant to ampicillin, cephazolin, fosfomycin and novobiocin. Phylogenetic analysis of VP1680 loci in 35 isolates from 17 asymptomatic workers, 6 gastroenteritis patients, 7 environmental samples and 5 genomes from a database showed 22 different alleles. Gene VP1680 was conserved in tdh+ isolates and pandemic strains, while that of trh + isolates was diverse. Asymptomatic workers carrying VP were the most likely source of contamination, which raises concerns over food safety in seafood-processing plants.

Vibrio parahaemolyticus: Basic Techniques for Growth, Genetic Manipulation, and Analysis of Virulence Factors

Vibrio parahaemolyticus is a Gram-negative, halophilic bacterium and opportunistic pathogen of humans and shrimp. Investigating the mechanisms of V. parahaemolyticus infection and the multifarious virulence factors it employs requires procedures for bacterial culture, genetic manipulation, and analysis of virulence phenotypes. Detailed protocols for growth assessment, generation of mutants, and phenotype assessment are included in this article. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Assessment of growth of V. parahaemolyticus Alternate Protocol 1: Assessment of growth of V. parahaemolyticus using a plate reader Basic Protocol 2: Swimming/swarming motility assay Basic Protocol 3: Genetic manipulation Alternate Protocol 2: Natural transformation Basic Protocol 4: Secretion assay and sample preparation for mass spectrometry analysis Basic Protocol 5: Invasion assay (gentamicin protection assay) Basic Protocol 6: Immunofluorescence detection of intracellular V. parahaemolyticus Basic Protocol 7: Cytotoxicity assay for T3SS2.

Delineating the key virulence factors and intraspecies divergence of Vibrio harveyi via whole-genome sequencing

Vibrio harveyi is one of the major pathogens in aquaculture. To identify the key virulence factors affecting pathogenesis of V. harveyi towards fish, we conducted a field investigation for three representative fish farms infected with V. harveyi. Multilocus sequence typing (MLST) and whole-genome sequencing were conducted to delineate the phylogenetic relationship and genetic divergence of V. harveyi. A total of 25 V. harveyi strains were isolated from the diseased fish and groundwater and were subtyped into 12 sequence types by MLST. Five virulence genes, mshB, pilA, hutR, ureB, and ureG, were variably presented in the sequenced strains. The virulence gene profiles strongly correlated with the distinct pathogenicity of V. harveyi strains, with a strain harboring all five genes exhibiting the highest virulence towards fish. Phenotype assay confirmed that reduced virulence correlated with decreased motility and biofilm formation ability. Additionally, three types of type VI secretion system, namely T6SS1, T6SS2, and T6SS3, were identified in V. harveyi strains, which can be classified into six, four, and 12 subtypes, respectively. In conclusion, the results indicated that the virulence level of V. harveyi is mainly determined by the above virulence genes, which may play vital roles in environmental adaptation for V. harveyi.

Type III Secretion 1 Effector Gene Diversity Among Vibrio Isolates From Coastal Areas in China

Vibrios, which include more than 120 valid species, are an abundant and diverse group of bacteria in marine and estuarine environments. Some of these bacteria have been recognized as pathogens of both marine animals and humans, and therefore, their virulence mechanisms have attracted increasing attention. The type III secretion system (T3SS) is an important virulence determinant in many gram-negative bacteria, in which this system directly translocates variable effectors into the host cytosol for the manipulation of the cellular responses. In this study, the distribution of the T3SS gene cluster was first examined in 110 Vibrio strains of 26 different species, including 98 strains isolated from coastal areas in China. Several T3SS1 genes, but not T3SS2 genes (T3SS2α and T3SS2β), were universally detected in all the strains of four species, Vibrio parahaemolyticus, Vibrio alginolyticus, Vibrio harveyi, and Vibrio campbellii. The effector coding regions within the T3SS1 gene clusters from the T3SS1-positive strains were further analyzed, revealing that variations in the effectors of Vibrio T3SS1 were observed among the four Vibrio species, even between different strains in V. harveyi, according to their genetic organization. Importantly, Afp17, a potential novel effector that may exert a similar function as the known effector VopS in T3SS1-induced cell death, based on cytotoxicity assay results, was found in the effector coding region of the T3SS1 in some V. harveyi and V. campbellii strains. Finally, it was revealed that differences in T3SS1-mediated cytotoxicity were dependent not only on the variations in the effectors of Vibrio T3SS1 but also on the initial adhesion ability to host cells, which is another prerequisite condition. Altogether, our results contribute to the clarification of the diversity of T3SS1 effectors and a better understanding of the differences in cytotoxicity among Vibrio species.

Taking Control: Campylobacter jejuni Binding to Fibronectin Sets the Stage for Cellular Adherence and Invasion

Campylobacter jejuni, a foodborne pathogen, is one of the most common bacterial causes of gastroenteritis in the world. Undercooked poultry, raw (unpasteurized) dairy products, untreated water, and contaminated produce are the most common sources associated with infection. C. jejuni establishes a niche in the gut by adhering to and invading epithelial cells, which results in diarrhea with blood and mucus in the stool. The process of colonization is mediated, in part, by surface-exposed molecules (adhesins) that bind directly to host cell ligands or the extracellular matrix (ECM) surrounding cells. In this review, we introduce the known and putative adhesins of the foodborne pathogen C. jejuni. We then focus our discussion on two C. jejuni Microbial Surface Components Recognizing Adhesive Matrix Molecule(s) (MSCRAMMs), termed CadF and FlpA, which have been demonstrated to contribute to C. jejuni colonization and pathogenesis. In vitro studies have determined that these two surface-exposed proteins bind to the ECM glycoprotein fibronectin (FN). In vivo studies have shown that cadF and flpA mutants exhibit impaired colonization of chickens compared to the wild-type strain. Additional studies have revealed that CadF and FlpA stimulate epithelial cell signaling pathways necessary for cell invasion. Interestingly, CadF and FlpA have distinct FN-binding domains, suggesting that the functions of these proteins are non-redundant. In summary, the binding of FN by C. jejuni CadF and FlpA adhesins has been demonstrated to contribute to adherence, invasion, and cell signaling.

Type III Secretion Effector VopQ of Vibrio parahaemolyticus Modulates Central Carbon Metabolism in Epithelial Cells

The metabolic response of host cells upon infection is pathogen specific, and infection-induced host metabolic reprogramming may have beneficial effects on the proliferation of pathogens. V. parahaemolyticus contains a range of virulence factors to manipulate host signaling pathways and metabolic processes. In this study, we identified that the T3SS1 VopQ effector rewrites host metabolism in conjunction with the inflammation and cell death processes. Understanding how VopQ reprograms host cell metabolism during the infection could help us to identify novel therapeutic strategies to enhance the survival of host cells during V. parahaemolyticus infection.

Vibrio parahaemolyticus is a Gram-negative halophilic pathogen that frequently causes acute gastroenteritis and occasional wound infection. V. parahaemolyticus contains several virulence factors, including type III secretion systems (T3SSs) and thermostable direct hemolysin (TDH). In particular, T3SS1 is a potent cytotoxic inducer, and T3SS2 is essential for causing acute gastroenteritis. Although much is known about manipulation of host signaling transductions by the V. parahaemolyticus effector, little is known about the host metabolomic changes modulated by V. parahaemolyticus. To address this knowledge gap, we performed a metabolomic analysis of the epithelial cells during V. parahaemolyticus infection using capillary electrophoresis-time of flight mass spectrometry (CE-TOF/MS). Our results revealed significant metabolomic perturbations upon V. parahaemolyticus infection. Moreover, we identified that T3SS1’s VopQ effector was responsible for inducing the significant metabolic changes in the infected cells. The VopQ effector dramatically altered the host cell’s glycolytic, tricarboxylic acid cycle (TCA), and amino acid metabolisms. VopQ effector disrupted host cell redox homeostasis by depleting cellular glutathione and subsequently increasing the level of reactive oxygen species (ROS) production.

IMPORTANCE The metabolic response of host cells upon infection is pathogen specific, and infection-induced host metabolic reprogramming may have beneficial effects on the proliferation of pathogens. V. parahaemolyticus contains a range of virulence factors to manipulate host signaling pathways and metabolic processes. In this study, we identified that the T3SS1 VopQ effector rewrites host metabolism in conjunction with the inflammation and cell death processes. Understanding how VopQ reprograms host cell metabolism during the infection could help us to identify novel therapeutic strategies to enhance the survival of host cells during V. parahaemolyticus infection.

Improvement and evaluation of loop-mediated isothermal amplification combined with chromatographic flow dipstick assays for Vibrio parahaemolyticus

Vibrio parahaemolyticus, a major food-borne pathogen, is a gram-negative rod-shaped halophilic bacterium which inhabits marine environments throughout the world. It can pose a threat to humans after the consumption of raw or undercooked seafood. Fast detection is crucial for hindering and controlling V. parahaemolyticus infection. Compared with traditional methods, loop-mediated isothermal amplification (LAMP) is a simple, rapid and versatile method. It can be performed at one temperature without the need for cycling. As a new method in recent years, LAMP combined with a chromatographic flow dipstick (LFD) meets the needs of point-of-care testing without the need for special instruments. It avoids the limitations of LAMP, reduces detection time and increases detection accuracy. Our previous studies have suggested that the optimized LFD method can improve the sensitivity of LAMP detection and shorten the isothermal amplification time during the detection process. In the present study, two LAMP assays were improved to LFD methods, and a LFD targeting 16S23S rRNA gene internal transcribed spacer (ITS) of V. parahaemolyticus was developed. The lower limit for tlh, toxR, ITS LFD assays were detected as 3.1 × 10⁰, 3.1 × 10¹, and 3.1 × 10⁰ CFU respectively, whether in pure cultures or artificially contaminated food samples. The shortest amplification times at the limit of each assay were determined as 20 min, 35 min and 25 min. A heating block was used to perform two (tlh and ITS) LFD assays to detect 20 food samples. Compared to a standard method (GB 4789.7-2013 National Food Safety Standards, Food Microbiology Inspection, Vibrio parahaemolyticus test), tlh and ITS LFD assays showed more MPN (most probable number) results than that of culture. It demonstrated that the improved LFD technology can provide a simple and rapid detection method with high sensitivity and specificity for detection of V. parahaemolyticus.

Integrative and Conjugative Elements-Positive Vibrio parahaemolyticus Isolated From Aquaculture Shrimp in Jiangsu, China

The development of multidrug- and toxin-resistant bacteria as a result of increasing industrialization and sustained and intense antimicrobial use in aquaculture results in human health problems through increased incidence of food-borne illnesses. Integrative and conjugative elements (ICEs) are self-transmissible mobile genetic elements that allow bacteria to acquire complex new traits through horizontal gene transfer and encode a wide variety of genetic information, including resistance to antibiotics and heavy metals; however, there is a lack of studies of ICEs of environmental origin in Asia. Here, we determined the prevalence, genotypes, heavy metal resistance and antimicrobial susceptibility of 997 presumptive strains of Vibrio parahaemolyticus (tlh⁺, tdh^–), a Gram-negative bacterium that causes gastrointestinal illness in humans, isolated from four species of aquaculture shrimp in Jiangsu, China. We found that 59 of the 997 isolates (5.9%) were ICE-positive, and of these, 9 isolates tested positive for all resistance genes. BLAST analysis showed that similarity for the eight strains to V. parahaemolyticus was 99%. Tracing the V. parahaemolyticus genotypes, showed no significant relevance of genotype among the antimicrobial resistance strains bearing the ICEs or not. Thus, in aquaculture, ICEs are not the major transmission mediators of resistance to antibiotics or heavy metals. We suggest future research to elucidate mechanisms that drive transmission of resistance determinants in V. parahaemolyticus.

Vibrio variations on a type three theme

Mounting evidence suggests that Type 3 Secretion Systems (T3SS) are widespread among Vibrio species, and are present in strains isolated from diverse sources such as human clinical infections, environmental reservoirs, and diseased marine life. Experiments evaluating Vibrio parahaemolyticus and Vibrio cholerae T3SS mediated virulence suggest that Vibrio T3SS pathogenicity islands have a tripartite composition. A conserved 'core' region encodes functions essential for colonization and disease in vivo, including modulation of innate immune signaling pathways and actin dynamics, whereas regions flanking core sequences are variable among strains and encode effector proteins performing a diverse array of activities. Characterizing novel functions associated with Vibrio-specific effectors is, therefore, essential for understanding how vibrios employ T3SS mechanisms to cause disease in a broad range of hosts and how T3SS island composition potentially defines species-specific disease.

QsvR integrates into quorum sensing circuit to control Vibrio parahaemolyticus virulence

Vibrio parahaemolyticus, the leading cause of seafood-associated gastroenteritis worldwide, requires the two type-III secretion systems (T3SS1 and T3SS2) and a thermostable direct hemolysin (encoded by tdh1 and tdh2) for full virulence. The tdh genes and the T3SS2 gene cluster constitute an 80 kb pathogenicity island known as Vp-PAI located on the chromosome II. Expression of T3SS1 and Vp-PAI is regulated in a quorum sensing (QS)-dependent manner but its detailed mechanisms remain unknown. Herein, we show that three factors (QS regulators AphA and OpaR and an AraC-type transcriptional regulator QsvR) form a complex regulatory network to control the expression of T3SS1 and Vp-PAI genes. At low cell density (LCD), whereas Vp-PAI expression is repressed, T3SS1 genes are induced by AphA, which directly binds (an operator region of) the exsBAD-vscBCD operon. At high cell density (HCD), the bacterium turns off T3SS1 expression by replacing AphA with OpaR, triggering the induction of Vp-PAI. Furthermore, QsvR binds to the regulatory regions of all the tested T3SS1 and Vp-PAI genes to activate their transcription at HCD. Taken together, our data highlight how multiple QS regulators contribute to the pathogenicity of V. parahaemolyticus by precisely controlling the expression of major virulence determinants during different stages of growth.

The Vibrio alginolyticus T3SS effectors, Val1686 and Val1680, induce cell rounding, apoptosis and lysis of fish epithelial cells

Vibrio alginolyticus is a Gram-negative bacterium that is an opportunistic pathogen of both marine animals and people. Its pathogenesis likely involves type III secretion system (T3SS) mediated induction of rapid apoptosis, cell rounding and osmotic lysis of infected eukaryotic cells. Herein, we report that effector proteins, Val1686 and Val1680 from V. alginolyticus, were responsible for T3SS-mediated death of fish cells. Val1686 is a Fic-domain containing protein that not only contributed to cell rounding by inhibiting Rho guanosine triphosphatases (GTPases), but was requisite for the induction of apoptosis because the deletion mutant (Δval1686) was severely weakened in its ability to induce cell rounding and apoptosis in fish cells. In addition, Val1686 alone was sufficient to induce cell rounding and apoptosis as evidenced by the transfection of Val1686 into fish cells. Importantly, the Fic-domain essential for cell rounding activity was equally important to activation of apoptosis of fish cells, indicating that apoptosis is a downstream event of Val1686-dependent GTPase inhibition. V. alginolyticus infection likely activates JNK and ERK pathways with sequential activation of caspases (caspase-8/-10, -9 and -3) and subsequent apoptosis. Val1680 contributed to T3SS-dependent lysis of fish cells in V. alginolyticus, but did not induce autophagy as has been reported for its homologue (VopQ) in V. parahaemolyticus. Together, Val1686 and Val1680 work together to induce apoptosis, cell rounding and cell lysis of V. alginolyticus-infected fish cells. These findings provide new insights into the mechanism of cell death caused by T3SS of V. alginolyticus.

The Transcriptional Regulator HlyU Positively Regulates Expression of exsA, Leading to Type III Secretion System 1 Activation in Vibrio parahaemolyticus

Vibrio parahaemolyticus is a marine bacterium that is globally recognized as the leading cause of seafood-borne gastroenteritis. V. parahaemolyticus uses various toxins and two type 3 secretion systems (T3SS-1 and T3SS-2) to subvert host cells during infection. We previously determined that V. parahaemolyticus T3SS-1 activity is upregulated by increasing the expression level of the master regulator ExsA under specific growth conditions. In this study, we set out to identify V. parahaemolyticus genes responsible for linking environmental and growth signals to exsA gene expression. Using transposon mutagenesis in combination with a sensitive and quantitative luminescence screen, we identify HlyU and H-NS as two antagonistic regulatory proteins controlling the expression of exsA and, hence, T3SS-1 in V. parahaemolyticus Disruption of hns leads to constitutive unregulated exsA gene expression, consistent with its known role in repressing exsA transcription. In contrast, genetic disruption of hlyU completely abrogated exsA expression and T3SS-1 activity. A V. parahaemolyticushlyU null mutant was significantly deficient for T3SS-1-mediated host cell death during in vitro infection. DNA footprinting studies with purified HlyU revealed a 56-bp protected DNA region within the exsA promoter that contains an inverted repeat sequence. Genetic evidence suggests that HlyU acts as a derepressor, likely by displacing H-NS from the exsA promoter, leading to exsA gene expression and appropriately regulated T3SS-1 activity. Overall, the data implicate HlyU as a critical positive regulator of V. parahaemolyticus T3SS-1-mediated pathogenesis.IMPORTANCE Many Vibrio species are zoonotic pathogens, infecting both animals and humans, resulting in significant morbidity and, in extreme cases, mortality. While many Vibrio species virulence genes are known, their associated regulation is often modestly understood. We set out to identify genetic factors of V. parahaemolyticus that are involved in activating exsA gene expression, a process linked to a type III secretion system involved in host cytotoxicity. We discover that V. parahaemolyticus employs a genetic regulatory switch involving H-NS and HlyU to control exsA promoter activity. While HlyU is a well-known positive regulator of Vibrio species virulence genes, this is the first report linking it to a transcriptional master regulator and type III secretion system paradigm.

Potential Survival and Pathogenesis of a Novel Strain, Vibrio parahaemolyticus FORC_022, Isolated From a Soy Sauce Marinated Crab by Genome and Transcriptome Analyses

Vibrio parahaemolyticus can cause gastrointestinal illness through consumption of seafood. Despite frequent food-borne outbreaks of V. parahaemolyticus, only 19 strains have subjected to complete whole-genome analysis. In this study, a novel strain of V. parahaemolyticus, designated FORC_022 (Food-borne pathogen Omics Research Center_022), was isolated from soy sauce marinated crabs, and its genome and transcriptome were analyzed to elucidate the pathogenic mechanisms. FORC_022 did not include major virulence factors of thermostable direct hemolysin (tdh) and TDH-related hemolysin (trh). However, FORC_022 showed high cytotoxicity and had several V. parahaemolyticus islands (VPaIs) and other virulence factors, such as various secretion systems (types I, II, III, IV, and VI), in comparative genome analysis with CDC_K4557 (the most similar strain) and RIMD2210633 (genome island marker strain). FORC_022 harbored additional virulence genes, including accessory cholera enterotoxin, zona occludens toxin, and tight adhesion (tad) locus, compared with CDC_K4557. In addition, O3 serotype specific gene and the marker gene of pandemic O3:K6 serotype (toxRS) were detected in FORC_022. The expressions levels of genes involved in adherence and carbohydrate transporter were high, whereas those of genes involved in motility, arginine biosynthesis, and proline metabolism were low after exposure to crabs. Moreover, the virulence factors of the type III secretion system, tad locus, and thermolabile hemolysin were overexpressed. Therefore, the risk of foodborne-illness may be high following consumption of FORC_022 contaminated crab. These results provided molecular information regarding the survival and pathogenesis of V. parahaemolyticus FORC_022 strain in contaminated crab and may have applications in food safety.

Role and regulation of the orphan AphA protein of quorum sensing in pathogenic Vibrios

Quorum sensing (QS), a cell-to-cell communication process, is widely distributed in the bacterial kingdom. Bacteria use QS to control gene expression in response to cell density by detecting the signal molecules called autoinducers. AphA protein is the master QS regulator of vibrios operating at low cell density. It regulates the expression of a variety of genes, especially those encoding virulence factors, flagella/motility and biofilm formation. The role and regulation of AphA in vibrios, especially in human pathogenic vibrios, are summarized in this review. Clarification of the roles of AphA will help us to understand the pathogenesis of vibrios.

Regulatory actions of ToxR and CalR on their own genes and type III secretion system 1 in Vibrio parahaemolyticus

Vibrio parahaemolyticus is the leading cause of seafood-associated gastroenteritis. Type III secretion system 1 (T3SS1) is one of the virulence determinants of this bacteria. T3SS1 expression is regulated by ToxR and CalR. ToxR represses the transcription of T3SS1 genes via activation of CalR, which acts as a transcriptional repressor of T3SS1 genes. However, the transcriptional regulation mechanisms have not been elucidated. As showing in the present work, ToxR binds to the promoter DNA region of calR to activate its transcription. CalR occupies the promoter-proximal regions of each detected target operons in T3SS1 loci to repress their transcription, and thereby inhibiting T3SS1-dependent cytotoxicity. Moreover, a feedback CalR inhibits toxR and its own gene in a direct manner. Collectively, this work reported an interesting gene regulatory network involving the reciprocal regulation of ToxR and CalR, and their regulation on T3SS1 genes transcription in V. parahaemolyticus.

T3SS effector VopL inhibits the host ROS response, promoting the intracellular survival of Vibrio parahaemolyticus

The production of antimicrobial reactive oxygen species by the nicotinamide dinucleotide phosphate (NADPH) oxidase complex is an important mechanism for control of invading pathogens. Herein, we show that the gastrointestinal pathogen Vibrio parahaemolyticus counteracts reactive oxygen species (ROS) production using the Type III Secretion System 2 (T3SS2) effector VopL. In the absence of VopL, intracellular V. parahaemolyticus undergoes ROS-dependent filamentation, with concurrent limited growth. During infection, VopL assembles actin into non-functional filaments resulting in a dysfunctional actin cytoskeleton that can no longer mediate the assembly of the NADPH oxidase at the cell membrane, thereby limiting ROS production. This is the first example of how a T3SS2 effector contributes to the intracellular survival of V. parahaemolyticus, supporting the establishment of a protective intracellular replicative niche.

Acute Hepatopancreatic Necrosis Disease-Causing Vibrio parahaemolyticus Strains Maintain an Antibacterial Type VI Secretion System with Versatile Effector Repertoires

Acute hepatopancreatic necrosis disease (AHPND) is a newly emerging shrimp disease that has severely damaged the global shrimp industry. AHPND is caused by toxic strains of Vibrio parahaemolyticus that have acquired a "selfish plasmid" encoding the deadly binary toxins PirA^vp/PirB^vp To better understand the repertoire of virulence factors in AHPND-causing V. parahaemolyticus, we conducted a comparative analysis using the genome sequences of the clinical strain RIMD2210633 and of environmental non-AHPND and toxic AHPND isolates of V. parahaemolyticus Interestingly, we found that all of the AHPND strains, but none of the non-AHPND strains, harbor the antibacterial type VI secretion system 1 (T6SS1), which we previously identified and characterized in the clinical isolate RIMD2210633. This finding suggests that the acquisition of this T6SS might confer to AHPND-causing V. parahaemolyticus a fitness advantage over competing bacteria and facilitate shrimp infection. Additionally, we found highly dynamic effector loci in the T6SS1 of AHPND-causing strains, leading to diverse effector repertoires. Our discovery provides novel insights into AHPND-causing pathogens and reveals a potential target for disease control.IMPORTANCE Acute hepatopancreatic necrosis disease (AHPND) is a serious disease that has caused severe damage and significant financial losses to the global shrimp industry. To better understand and prevent this shrimp disease, it is essential to thoroughly characterize its causative agent, Vibrio parahaemolyticus Although the plasmid-encoded binary toxins PirA^vp/PirB^vp have been shown to be the primary cause of AHPND, it remains unknown whether other virulent factors are commonly present in V. parahaemolyticus and might play important roles during shrimp infection. Here, we analyzed the genome sequences of clinical, non-AHPND, and AHPND strains to characterize their repertoires of key virulence determinants. Our studies reveal that an antibacterial type VI secretion system is associated with the AHPND strains and differentiates them from non-AHPND strains, similar to what was seen with the PirA/PirB toxins. We propose that T6SS1 provides a selective advantage during shrimp infections.

The cytotoxic type 3 secretion system 1 of Vibrio rewires host gene expression to subvert cell death and activate cell survival pathways

Bacterial effectors potently manipulate host signaling pathways. The marine bacterium Vibrio parahaemolyticus (V. para) delivers effectors into host cells through two type 3 secretion systems (T3SSs). T3SS1 is vital for V. para survival in the environment, whereas T3SS2 causes acute gastroenteritis in human hosts. Although the natural host is undefined, T3SS1 effectors attack highly conserved cellular processes and pathways to orchestrate nonapoptotic cell death. To understand how the concerted action of T3SS1 effectors globally affects host cell signaling, we compared gene expression changes over time in primary fibroblasts infected with V. para that have a functional T3SS1 (T3SS1⁺) to those in cells infected with V. para lacking T3SS1 (T3SS1^-). Overall, the host transcriptional response to both T3SS1⁺ and T3SS1^-V. para was rapid, robust, and temporally dynamic. T3SS1 rewired host gene expression by specifically altering the expression of 398 genes. Although T3SS1 effectors targeted host cells at the posttranslational level to cause cytotoxicity, V. para T3SS1 also precipitated a host transcriptional response that initially activated cell survival and repressed cell death networks. The increased expression of several key prosurvival transcripts mediated by T3SS1 depended on a host signaling pathway that is silenced posttranslationally later in infection. Together, our analysis reveals a complex interplay between the roles of T3SS1 as both a transcriptional and posttranslational manipulator of host cell signaling.

Bile Sensing: The Activation of Vibrio parahaemolyticus Virulence

Bacteria must develop resistance to various inhospitable conditions in order to survive in the human gastrointestinal tract. Bile, which is secreted by the liver, and plays an important role in food digestion also has antimicrobial properties and is able to disrupt cellular homeostasis. Paradoxically, although bile is one of the guts defenses, many studies have reported that bacteria such as Vibrio parahaemolyticus can sense bile and use its presence as an environmental cue to upregulate virulence genes during infection. This article aims to discuss how bile is detected by V. parahaemolyticus and its role in regulating type III secretion system 2 leading to human infection. This bile–bacteria interaction pathway gives us a clearer understanding of the biochemical and structural analysis of the bacterial receptors involved in mediating a response to bile salts which appear to be a significant environmental cue during initiation of an infection.

Actin cytoskeleton-modulating T3SS2 effectors and their contribution to the Vibrio parahaemolyticus-induced diarrhea

To understand how bacterial pathogens cause diseases is the most important step in order to prevent the infection and develop an effective treatment. However, the past proceeding studies make us aware of quite-complicated interactions between the host and pathogenic bacteria. Vibrio parahaemolyticus, a food-born pathogen that is a subject of our study, causes inflammatory diarrhea in human upon ingestion of contaminated raw or undercooked seafood. Many virulence factors has been proposed since its discovery in Osaka around 70 years ago, while our research group has revealed that one of these virulence factors, type 3 secretion system 2 (T3SS2), is necessary for diarrhea induced by this bacterium. In addition, we recently found two novel T3SS2 effectors (VopO and VopV) that manipulate the actin cytoskeleton in infected host cells. In this article, I would like to show our findings with regard to biological activities of the effectors and their contributions to the T3SS2-induced enterotoxicity.

Complete genome sequence of Vibrio parahaemolyticus FORC_023 isolated from raw fish storage water

Vibrio parahaemolyticusis a Gram-negative halophilic bacterium that causes food-borne gastroenteritis in humans who consumeV. parahaemolyticus-contaminated seafood.The FORC_023 strain was isolated from raw fish storage water, containing live fish at a sashimi restaurant. Here, we aimed to sequence and characterize the genome of the FORC_023 strain. The genome of the FORC_023 strain showed two circular chromosomes, which contained 4227 open reading frames (ORFs), 131 tRNA genes and 37 rRNA genes. Although the genome of FORC_023 did not include major virulence genes, such as genes encoding thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH), it contained genes encoding other hemolysins, secretion systems, iron uptake-related proteins and severalV. parahaemolyticusislands. The highest average nucleotide identity value was obtained between the FORC_023 strain and UCM-V493 (CP007004-6). Comparative genomic analysis of FORC_023 with UCM-V493 revealed that FORC_023 carried an additional genomic region encoding virulence factors, such as repeats-in-toxin and type II secretion factors. Furthermore,in vitrocytotoxicity testing showed that FORC_023 exhibited a high level of cytotoxicity toward INT-407 human epithelial cells. These results suggested that the FORC_023 strain may be a food-borne pathogen.

Transcriptional profiling of Vibrio parahaemolyticus exsA reveals a complex activation network for type III secretion

Vibrio parahaemolyticus (Vp) is a marine halophilic bacterium that is commonly associated with oysters and shrimp. Human consumption of contaminated shellfish can result in Vp mediated gastroenteritis and severe diarrheal disease. Vp encodes two type 3 secretion systems (T3SS-1 and T3SS2) that have been functionally implicated in cytotoxicity and enterotoxicity respectively. In this study, we profiled protein secretion and temporal promoter activities associated with exsA and exsB gene expression. exsA is an AraC-like transcriptional activator that is critical for activating multiple operons that encode T3SS-1 genes, whereas exsB is thought to encode an outer membrane pilotin component for T3SS-1. The exsBA genetic locus has two predicted promoter elements. The predicted exsB and exsA promoters were individually cloned upstream of luxCDABE genes in reporter plasmid constructs allowing for in situ, real-time quantitative light emission measurements under many growth conditions. Low calcium growth conditions supported maximal exsB and exsA promoter activation. exsB promoter activity exhibited high basal activity and resulted in an exsBA co-transcript. Furthermore, a separate proximal exsA promoter showed initial low basal activity yet eventually exceeded that of exsB and reached maximal levels after 2.5 h corresponding to an entry into early log phase. exsA promoter activity was significantly higher at 30°C than 37°C, which also coincided with increased secretion levels of specific T3SS-1 effector proteins. Lastly, bioinformatic analyses identified a putative expanded ExsA binding motif for multiple transcriptional operons. These findings suggest a two wave model of Vp T3SS-I induction that integrates two distinct promoter elements and environmental signals into a complex ExsA activation framework.

The small RNA Spot 42 regulates the expression of the type III secretion system 1 (T3SS1) chaperone protein VP1682 in Vibrio parahaemolyticus

The cytotoxicity of Vibrio parahaemolyticus has been related to the type III secretion system 1 effector protein VP1680, which is secreted and translocated into host cells with the help of the specific chaperone protein, VP1682. This study sought to confirm the in silico analysis, which predicted that a small regulatory RNA (Spot 42) could base pair with the region encompassing the ribosomal-binding site and initiation codon of the vp1682 mRNA. Electrophoresis mobility shift assays indicated that Spot 42 could bind to the vp1682 mRNA with the help of Hfq. Consistent with these results, the translation of the vp1682 mRNA was inhibited when both Hfq and Spot 42 were added to the in vitro translation reaction. The cytotoxic activity against infected Caco-2 cells was significantly increased in the Spot 42 deletion mutant (Δspf) at 4 h after infection as compared with the parental strain. Additionally, we observed that both VP1682 and VP1680 were more highly expressed in Δspf mutants than in the parental strain. These results indicate that Spot 42 post-transcriptionally regulates the expression of VP1682 in V. parahaemolyticus, which contributes to cytotoxicity in vivo.

Identification and Purification of the CPD Photolyase in Vibrio parahaemolyticus RIMD2210633

Photoreactivation is an error-free mechanism of DNA repair, utilized by prokaryotes and most eukaryotes and is catalyzed by specific enzymes called DNA photolyases. Photoreactivation has been reported in Vibrio parahaemolyticus WP28; however, information on photolyases in V. parahaemolyticus (V.p) strains has not been reported. This study examined the photoreactivation in V.p RIMD2210633. The photolyase responsible for repairing cyclobutane pyrimidine dimer (CPD) in DNA was identified, and the corresponding gene was determined as VPA1471. The protein was overexpressed in Escherichia coli and was purified for functional assessment in vitro. The mRNA level and protein expression level of this gene increased after ultraviolet A (UVA) illumination following ultraviolet C (UVC) irradiation. In vitro experiments confirmed that the protein encoded by VPA1471 could reduce the quantity of CPD in DNA. We designated the corresponding gene and protein of VPA1471 phr and Phr, respectively, although the function of two other photolyase/cryptochrome family members, VPA0203 and VPA0204, remains unclear. UV (ultraviolet) irradiation experiments suggest that these two genes possess some photorepairing ability. Therefore, we hypothesize that VPA0203 and VPA0204 encode (6-4) photolyase in V. parahaemolyticus RIMD2210633.

Comparative secretomics reveals novel virulence-associated factors of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a causative agent of serious human seafood-borne gastroenteritis disease and even death. In this study, for the first time, we obtained the secretomic profiles of seven V. parahaemolyticus strains of clinical and food origins. The strains exhibited various toxic genotypes and phenotypes of antimicrobial susceptibility and heavy metal resistance, five of which were isolated from aquatic products in Shanghai, China. Fourteen common extracellular proteins were identified from the distinct secretomic profiles using the two-dimensional gel electrophoresis (2-DE) and liquid chromatography tandem mass spectrometry (LC-MS/MS) techniques. Of these, half were involved in protein synthesis and sugar transport of V. parahaemolyticus. Strikingly, six identified proteins were virulence-associated factors involved in the pathogenicity of some other pathogenic bacteria, including the translation elongation factor EF-Tu, pyridoxine 5′-phosphate synthase, σ⁵⁴ modulation protein, dihydrolipoyl dehydrogenase, transaldolase and phosphoglycerate kinase. In addition, comparative secretomics also revealed several extracellular proteins that have not been described in any bacteria, such as the ribosome-recycling factor, translation elongation factor EF-Ts, phosphocarrier protein HPr and maltose-binding protein MalE. The results in this study will facilitate the better understanding of the pathogenesis of V. parahaemolyticus and provide data in support of novel vaccine candidates against the leading seafood-borne pathogen worldwide.

DNA-Binding Protein HU Coordinates Pathogenicity in Vibrio parahaemolyticus

HU is one of the most abundant nucleoid-associated proteins in bacterial cells and regulates the expression of many genes involved in growth, motility, metabolism, and virulence. It is known that Vibrio parahaemolyticus pathogenicity is related to its characteristic rapid growth and that type III secretion system 1 (T3SS1) contributes to its cytotoxicity. However, it is not known if HU plays a role in the pathogenicity of V. parahaemolyticus. In the present study, we investigated the effect of HU proteins HU-2 (HUα) (V. parahaemolyticus 2911 [vp2911]) and HUβ (vp0920) on the pathogenicity of V. parahaemolyticus. We found that a deletion of both HU subunits (yielding the ΔHUs [Δvp0920 Δvp2911] strain), but not single deletions, led to a reduction of the growth rate. In addition, expression levels of T3SS1-related genes, including exsA (positive regulator), exsD (negative regulator), vp1680 (cytotoxic effector), and vp1671 (T3SS1 apparatus), were reduced in the ΔHUs strain compared to the wild type (WT). As a result, cytotoxicity to HeLa cells was decreased in the ΔHUs strain. The additional deletion of exsD in the ΔHUs strain restored T3SS1-related gene expression levels and cytotoxicity but not the growth rate. These results suggest that the HU protein regulates the levels of T3SS1 gene expression and cytotoxicity in a growth rate-independent manner.

IMPORTANCE

Nucleoid-binding protein HU regulates cellular behaviors, including nucleoid structuring, general recombination, transposition, growth, replication, motility, metabolism, and virulence. It is thought that both the number of bacteria and the number of virulence factors may affect the pathogenicity of bacteria. In the present study, we investigated which factor(s) has a dominant role during infection in one of the most rapidly growing bacterial species, Vibrio parahaemolyticus. We found that V. parahaemolyticus cytotoxicity is regulated, in a growth rate-independent manner, by the HU proteins through regulation of a number of virulence factors, including T3SS1 gene expression.

The First Report of Vibrio parahaemolyticus Strain O10:K60 in Japan, a New Combination of O and K Serotypes Isolated from a Patient with Gastroenteritis

Vibrio parahaemolyticus is an important pathogen that causes gastroenteritis in humans, generally associated with the consumption of contaminated seafood, particularly raw shellfish. There are many serotypes in V. parahaemolyticus resulting from a combination of O and K antigens. Among them, O3:K6 and their variants, which represent the pandemic clone, are the most widespread strains worldwide. In this study, we examined V. parahaemolyticus isolated from a gastroenteritis patient's stool at a hospital in Saitama City, Japan in 2013. Serotyping of the O and K antigens identified the strain as O10:K60. To our knowledge, this is the first reported case of a V. parahaemolyticus strain with this antigen combination in Japan. Subsequently, we used PCR to assay for pathogenicity-associated genes, and found that it was positive for tdh, T3SS1, and T3SS2α genes. Antibiotic susceptibility tests showed that the strain was susceptible to all selected antibiotics except ampicillin. Moreover, we detected specific marker genes for the pandemic clone with two kinds of PCR assay. Our results suggest that the isolate O10:K60 is a newly emerging serotype that belongs to the pandemic clone.

Insights into the environmental reservoir of pathogenic Vibrio parahaemolyticus using comparative genomics

Vibrio parahaemolyticus is an aquatic halophilic bacterium that occupies estuarine and coastal marine environments, and is a leading cause of seafood-borne food poisoning cases. To investigate the environmental reservoir and potential gene flow that occurs among V. parahaemolyticus isolates, the virulence-associated gene content and genome diversity of a collection of 133 V. parahaemolyticus isolates were analyzed. Phylogenetic analysis of housekeeping genes, and pulsed-field gel electrophoresis, demonstrated that there is genetic similarity among V. parahaemolyticus clinical and environmental isolates. Whole-genome sequencing and comparative analysis of six representative V. parahaemolyticus isolates was used to identify genes that are unique to the clinical and environmental isolates examined. Comparative genomics demonstrated an O3:K6 environmental isolate, AF91, which was cultured from sediment collected in Florida in 2006, has significant genomic similarity to the post-1995 O3:K6 isolates. However, AF91 lacks the majority of the virulence-associated genes and genomic islands associated with these highly virulent post-1995 O3:K6 genomes. These findings demonstrate that although they do not contain most of the known virulence-associated regions, some V. parahaemolyticus environmental isolates exhibit significant genetic similarity to clinical isolates. This highlights the dynamic nature of the V. parahaemolyticus genome allowing them to transition between aquatic and host-pathogen states.

The pathogenesis, detection, and prevention of Vibrio parahaemolyticus

Vibrio parahaemolyticus, a Gram-negative motile bacterium that inhabits marine and estuarine environments throughout the world, is a major food-borne pathogen that causes life-threatening diseases in humans after the consumption of raw or undercooked seafood. The global occurrence of V. parahaemolyticus accentuates the importance of investigating its virulence factors and their effects on the human host. This review describes the virulence factors of V. parahaemolyticus reported to date, including hemolysin, urease, two type III secretion systems and two type VI secretion systems, which both cause both cytotoxicity in cultured cells and enterotoxicity in animal models. We describe various types of detection methods, based on virulence factors, that are used for quantitative detection of V. parahaemolyticus in seafood. We also discuss some useful preventive measures and therapeutic strategies for the diseases mediated by V. parahaemolyticus, which can reduce, to some extent, the damage to humans and aquatic animals attributable to V. parahaemolyticus. This review extends our understanding of the pathogenic mechanisms of V. parahaemolyticus mediated by virulence factors and the diseases it causes in its human host. It should provide new insights for the diagnosis, treatment, and prevention of V. parahaemolyticus infection.

H-NS is a repressor of major virulence gene loci in Vibrio parahaemolyticus

Vibrio parahaemolyticus, a leading cause of seafood-associated diarrhea and gastroenteritis, harbors three major virulence gene loci T3SS1, Vp-PAI (T3SS1+tdh2) and T6SS2. As showing in this study, the nucleoid-associated DNA-binding regulator H-NS binds to multiple promoter-proximal regions in each of the above three loci to repress their transcription, and moreover H-NS inhibits the cytotoxicitiy, enterotoxicity, hemolytic activity, and mouse lethality of V. parahaemolyticus. H-NS appears to act as a major repressor of the virulence of this pathogen. Date presented here would promote us to gain a deeper understanding of H-NS-mediated silencing of horizontally acquired virulence loci in V. parahaemolyticus.

Vibrio parahaemolyticus: a review on the pathogenesis, prevalence, and advance molecular identification techniques

Vibrio parahaemolyticus is a Gram-negative halophilic bacterium that is found in estuarine, marine and coastal environments. V. parahaemolyticus is the leading causal agent of human acute gastroenteritis following the consumption of raw, undercooked, or mishandled marine products. In rare cases, V. parahaemolyticus causes wound infection, ear infection or septicaemia in individuals with pre-existing medical conditions. V. parahaemolyticus has two hemolysins virulence factors that are thermostable direct hemolysin (tdh)-a pore-forming protein that contributes to the invasiveness of the bacterium in humans, and TDH-related hemolysin (trh), which plays a similar role as tdh in the disease pathogenesis. In addition, the bacterium is also encodes for adhesions and type III secretion systems (T3SS1 and T3SS2) to ensure its survival in the environment. This review aims at discussing the V. parahaemolyticus growth and characteristics, pathogenesis, prevalence and advances in molecular identification techniques.

Comparative RNA-Seq based dissection of the regulatory networks and environmental stimuli underlying Vibrio parahaemolyticus gene expression during infection

Vibrio parahaemolyticus is the leading worldwide cause of seafood-associated gastroenteritis, yet little is known regarding its intraintestinal gene expression or physiology. To date, in vivo analyses have focused on identification and characterization of virulence factors—e.g. a crucial Type III secretion system (T3SS2)—rather than genome-wide analyses of in vivo biology. Here, we used RNA-Seq to profile V. parahaemolyticus gene expression in infected infant rabbits, which mimic human infection. Comparative transcriptomic analysis of V. parahaemolyticus isolated from rabbit intestines and from several laboratory conditions enabled identification of mRNAs and sRNAs induced during infection and of regulatory factors that likely control them. More than 12% of annotated V. parahaemolyticus genes are differentially expressed in the intestine, including the genes of T3SS2, which are likely induced by bile-mediated activation of the transcription factor VtrB. Our analyses also suggest that V. parahaemolyticus has access to glucose or other preferred carbon sources in vivo, but that iron is inconsistently available. The V. parahaemolyticus transcriptional response to in vivo growth is far more widespread than and largely distinct from that of V. cholerae, likely due to the distinct ways in which these diarrheal pathogens interact with and modulate the environment in the small intestine.

Intracellular Vibrio parahaemolyticus escapes the vacuole and establishes a replicative niche in the cytosol of epithelial cells

Vibrio parahaemolyticus is a globally disseminated Gram-negative marine bacterium and the leading cause of seafood-borne acute gastroenteritis. Pathogenic bacterial isolates encode two type III secretion systems (T3SS), with the second system (T3SS2) considered the main virulence factor in mammalian hosts. For many decades, V. parahaemolyticus has been studied as an exclusively extracellular bacterium. However, the recent characterization of the T3SS2 effector protein VopC has suggested that this pathogen has the ability to invade, survive, and replicate within epithelial cells. Herein, we characterize this intracellular lifestyle in detail. We show that following internalization, V. parahaemolyticus is contained in vacuoles that develop into early endosomes, which subsequently mature into late endosomes. V. parahaemolyticus then escapes into the cytoplasm prior to vacuolar fusion with lysosomes. Vacuolar acidification is an important trigger for this escape. The cytoplasm serves as the pathogen's primary intracellular replicative niche; cytosolic replication is rapid and robust, with cells often containing over 150 bacteria by the time of cell lysis. These results show how V. parahaemolyticus successfully establishes an intracellular lifestyle that could contribute to its survival and dissemination during infection.

IMPORTANCE

The marine bacterium V. parahaemolyticus is the leading cause worldwide of seafood-borne acute gastroenteritis. For decades, the pathogen has been studied exclusively as an extracellular bacterium. However, recent results have revealed the pathogen's ability to invade and replicate within host cells. The present study is the first characterization of the V. parahaemolyticus' intracellular lifestyle. Upon internalization, V. parahaemolyticus is contained in a vacuole that would in the normal course of events ultimately fuse with a lysosome, degrading the vacuole's contents. The bacterium subverts this pathway, escaping into the cytoplasm prior to lysosomal fusion. Once in the cytoplasm, it replicates prolifically. Our study provides new insights into the strategies used by this globally disseminated pathogen to survive and proliferate within its host.

Effectors of animal and plant pathogens use a common domain to bind host phosphoinositides

Bacterial Type III Secretion Systems deliver effectors into host cells to manipulate cellular processes to the advantage of the pathogen. Many host targets of these effectors are found on membranes. Therefore, to identify their targets, effectors often use specialized membrane-localization domains to localize to appropriate host membranes. However, the molecular mechanisms used by many domains are unknown. Here we identify a conserved bacterial phosphoinositide-binding domain (BPD) that is found in functionally diverse Type III effectors of both plant and animal pathogens. We show that members of the BPD family functionally bind phosphoinositides and mediate localization to host membranes. Moreover, NMR studies reveal that the BPD of the newly identified Vibrio parahaemolyticus Type III effector VopR is unfolded in solution, but folds into a specific structure upon binding its ligand phosphatidylinositol-(4,5)-bisphosphate. Thus, our findings suggest a possible mechanism for promoting refolding of Type III effectors after delivery into host cells.