Vibrio parahaemolyticus inhibition of Rho family GTPase activation requires a functional chromosome I type III secretion system

Unveiling potential virulence determinants in Vibrio isolates from Anadara tuberculosa through whole genome analyses

The genus Vibrio includes pathogenic bacteria able to cause disease in humans and aquatic organisms, leading to disease outbreaks and significant economic losses in the fishery industry. Despite much work on Vibrio in several marine organisms, no specific studies have been conducted on Anadara tuberculosa. This is a commercially important bivalve species, known as "piangua hembra," along Colombia's Pacific coast. Therefore, this study aimed to identify and characterize the genomes of Vibrio isolates obtained from A. tuberculosa. Bacterial isolates were obtained from 14 A. tuberculosa specimens collected from two locations along the Colombian Pacific coast, of which 17 strains were identified as Vibrio: V. parahaemolyticus (n = 12), V. alginolyticus (n = 3), V. fluvialis (n = 1), and V. natriegens (n = 1). Whole genome sequence of these isolates was done using Oxford Nanopore Technologies (ONT). The analysis revealed the presence of genes conferring resistance to β-lactams, tetracyclines, chloramphenicol, and macrolides, indicating potential resistance to these antimicrobial agents. Genes associated with virulence were also found, suggesting the potential pathogenicity of these Vibrio isolates, as well as genes for Type III Secretion Systems (T3SS) and Type VI Secretion Systems (T6SS), which play crucial roles in delivering virulence factors and in interbacterial competition. This study represents the first genomic analysis of bacteria within A. tuberculosa, shedding light on Vibrio genetic factors and contributing to a comprehensive understanding of the pathogenic potential of these Vibrio isolates.IMPORTANCEThis study presents the first comprehensive report on the whole genome analysis of Vibrio isolates obtained from Anadara tuberculosa, a bivalve species of great significance for social and economic matters on the Pacific coast of Colombia. Research findings have significant implications for the field, as they provide crucial information on the genetic factors and possible pathogenicity of Vibrio isolates associated with A. tuberculosa. The identification of antimicrobial resistance genes and virulence factors within these isolates emphasizes the potential risks they pose to both human and animal health. Furthermore, the presence of genes associated with Type III and Type VI Secretion Systems suggests their critical role in virulence and interbacterial competition. Understanding the genetic factors that contribute to Vibrio bacterial virulence and survival strategies within their ecological niche is of utmost importance for the effective prevention and management of diseases in aquaculture practices.

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 patterns and influence of the two-component system in Vibrio parahaemolyticus of different genotypes

Vibrio parahaemolyticus is a foodborne pathogen that threatens global food security and human health. The two-component system (TCS) is a primary method for bacteria self-regulate and adapt to the environment. Previous studies have shown that V. parahaemolyticus has four hemolytic genotypes with diverse biological phenotypes and environmental adaptability, but the mechanism is unclear. In this study, we investigated TCS expression patterns in V. parahaemolyticus with different genotypes for the first time and explored the differences in TCS between strains. The results showed similarities in the TCS expression pattern between VPC17 (tdh+/trh-) and VPC44 (tdh-/trh-), while VPC85(tdh-/trh+) had the least similar TCS expression pattern to the other three strains. Analysis of biological information revealed that different regulations of C4 dicarboxylate transport, tetrathionate uptake, antibiotic resistance, and flagellar synthesis involved in the TCS might influence strains' growth, antibiotic resistance, biofilm, and virulence. The different TCS regulatory abilities of strains might be one of the reasons for diverse biological characteristics and different environmental adaptations. This work provides a theoretical basis and a new research direction for the strain variability of V. parahaemolyticus.

Functional characterization of T3SS C-ring component VscQ and evaluation of its mutant as a live attenuated vaccine in zebrafish (Danio rerio) model

Vibrio alginolyticus, a Gram-negative bacterium, has been recognized as an opportunistic pathogen in marine animals as well as humans. Type III secretion system (T3SS) is critical for pathogen virulence and disease development. However, no more information is known about the C-ring component VscQ and its physiological role. In this study, gene vscQ was cloned from V. alginolyticus wild-type strain HY9901 and the mutant strain HY9901ΔvscQ was constructed by the in-frame deletion method. The HY9901ΔvscQ mutant showed an attenuated swarming phenotype and a closely 4.6-fold decrease in the virulence to Danio rerio. However, the HY9901ΔvscQ mutant showed no difference in growth, biofilm formation and ECPase activity. HY9901ΔvscQ reduces the release of LDH, NO and caspase-3 activity of infected FHM cell, which are involved in fish cell apoptosis. Deletion of gene vscQ downregulates the expression level of T3SS-related genes including vscL, vopB, hop, vscO, vscK, vopD, vcrV and vopS and flagellum-related genes (flaA and fliG). And Danio rerio vaccinated via i.m injection with HY9901ΔvscQ induced a relative percent survival (RPS) value of 71% after challenging with the wild-type HY9901. Real-time PCR assays showed that vaccination with HY9901ΔvscQ enhanced the expression of immune-related genes, including TNF-α, TLR5, IL-6R, IgM and c/ebpβ in liver and spleen after vaccination, indicating that it is able to induce humoral and cell-mediated immune response in zebrafish. These results demonstrate that the HY9901ΔvscQ mutant could be used as an effective live vaccine to combat V. alginolyticus infection.

Molecular mechanisms of Vibrio parahaemolyticus pathogenesis

Vibrio parahaemolyticus is a Gram-negative halophilic bacterium that is mainly distributed in the seafood such as fish, shrimps and shellfish throughout the world. V. parahaemolyticus can cause diseases in marine aquaculture, leading to huge economic losses to the aquaculture industry. More importantly, it is also the leading cause of seafood-borne diarrheal disease in humans worldwide. With the development of animal model, next-generation sequencing as well as biochemical and cell biological technologies, deeper understanding of the virulence factors and pathogenic mechanisms of V. parahaemolyticus has been gained. As a globally transmitted pathogen, the pathogenicity of V. parahaemolyticus is closely related to a variety of virulence factors. This article comprehensively reviewed the molecular mechanisms of eight types of virulence factors: hemolysin, type III secretion system, type VI secretion system, adhesion factor, iron uptake system, lipopolysaccharide, protease and outer membrane proteins. This review comprehensively summarized our current understanding of the virulence factors in V. parahaemolyticus, which are potentially new targets for the development of therapeutic and preventive strategies.

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.

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 Rho signalling pathway mediates the pathogenicity of AHPND-causing V. parahaemolyticus in shrimp

An emerging bacterial disease, acute hepatopancreatic necrosis disease (AHPND), is caused by strains of Vibrio parahaemolyticus with an additional AHPND-associated plasmid pVA1 encoding a virulent toxin (Pir^vp ) that damages the shrimp's hepatopancreas. Like other species of Vibrio, these virulent strains initially colonise the shrimp's stomach, but it is not yet understood how the bacteria or toxins are subsequently able to cross the epithelial barrier and reach the hepatopancreas. Here, by using transcriptomics and system biology methods, we investigate AHPND-induced changes in the stomach of AHPND-causing V. parahaemolyticus (5HP)-infected shrimp and identify host molecular mechanisms that might explain how the integrity of the stomach barrier is compromised. We found that the expression of 376 unique genes was differentially regulated by AHPND infection. Gene ontology, protein interaction, and gene-to-gene correlation expression interaction analyses indicated that in addition to the immune system, a number of these genes were involved in cytoskeleton regulation by Rho GTPase. The involvement of Rho pathway regulation during AHPND pathogenesis was further supported by experiments showing that while Rho inhibitor pretreatment delayed the infection, pretreatment with Rho activator enhanced the pathogenicity of 5HP, and both the bacteria and toxin were detected sooner in the hepatopancreas. Further, disruption of the stomach epithelial structure was found in both Rho preactivated shrimp and in 5HP-infected shrimp. Taken together, we interpret our results to mean that Rho signalling helps to mediate AHPND pathogenesis in shrimp.

Characteristics of Vibrio parahaemolyticus isolates obtained from crayfish (Procambarus clarkii) in freshwater

Vibrio parahaemolyticus usually occurs in coastal areas and is generally recognized as a marine bacterium. It has become the leading cause of gastroenteritis worldwide. In the present study, 96 V. parahaemolyticus isolates were obtained from freshwater crayfish (Procambarus clarkii) and classified by multilocus sequence typing. Fifty-three sequence types (STs) were identified among the 96 isolates analyzed, 38 of which were novel STs. These isolates fell into six groups and 42 singletons, suggesting a high level of genetic diversity. Screening for 9 virulence and virulence-related genes in the isolates revealed that 40 isolates contained more than two genes with possible roles in pathogenicity. The virulence of the representative isolates VP66 (trh⁺, ureC⁺, T3SS1⁺, T3SS2β⁺, T6SS2⁺) and VP80 (T3SS1⁺, T6SS1⁺, T6SS2⁺) were further assessed in zebrafish and mouse infection model in vivo, and the tested isolates were shown to be lethal to both zebrafish and mice. These results suggest that crayfish may serve as a carrier of V. parahaemolyticus in freshwater, and that some isolates may have the potential to cause foodborne disease in humans.

Biological Diversity and Molecular Plasticity of FIC Domain Proteins

The ubiquitous proteins with FIC (filamentation induced by cyclic AMP) domains use a conserved enzymatic machinery to modulate the activity of various target proteins by posttranslational modification, typically AMPylation. Following intensive study of the general properties of FIC domain catalysis, diverse molecular activities and biological functions of these remarkably versatile proteins are now being revealed. Here, we review the biological diversity of FIC domain proteins and summarize the underlying structure-function relationships. The original and most abundant genuine bacterial FIC domain proteins are toxins that use diverse molecular activities to interfere with bacterial physiology in various, yet ill-defined, biological contexts. Host-targeted virulence factors have evolved repeatedly out of this pool by exaptation of the enzymatic FIC domain machinery for the manipulation of host cell signaling in favor of bacterial pathogens. The single human FIC domain protein HypE (FICD) has a specific function in the regulation of protein stress responses.

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.

Transcriptome analysis of Vibrio parahaemolyticus in type III secretion system 1 inducing conditions

Vibrio parahaemolyticus is an emerging bacterial pathogen capable of causing inflammatory gastroenteritis, wound infections, and septicemia. As a food-borne illness, infection is most frequently associated with the consumption of raw or undercooked seafood, particularly shellfish. It is the primary cause of Vibrio-associated food-borne illness in the United States and the leading cause of food-borne illness in Japan. The larger of its two chromosomes harbors a set of genes encoding type III section system 1 (T3SS1), a virulence factor present in all V. parahaemolyticus strains that is similar to the Yersinia ysc T3SS. T3SS1 translocates effector proteins into eukaryotic cells where they induce changes to cellular physiology and modulate host-pathogen interactions. T3SS1 is also responsible for cytotoxicity toward several different cultured cell lines as well as mortality in a mouse model. Herein we used RNA-seq to obtain global transcriptome patterns of V. parahaemolyticus under conditions that either induce [growth in Dulbecco's Modified Eagle Medium (DMEM) media, in trans expression of transcriptional regulator exsA] or repress T3SS1 expression (growth in LB-S media, in trans exsD expression) and during infection of HeLa cells over time. Comparative transcriptomic analysis demonstrated notable differences in the expression patterns under inducing conditions and was also used to generate an expression profile of V. parahaemolyticus during infection of HeLa cells. In addition, we identified several new genes that are associated with T3SS1 expression and may warrant further study.

Manipulation of intestinal epithelial cell function by the cell contact-dependent type III secretion systems of Vibrio parahaemolyticus

Vibrio parahaemolyticus elicits gastroenteritis by deploying Type III Secretion Systems (TTSS) to deliver effector proteins into epithelial cells of the human intestinal tract. The bacteria must adhere to the human cells to allow colonization and operation of the TTSS translocation apparatus bridging the bacterium and the host cell. This article first reviews recent advances in identifying the molecules responsible for intercellular adherence. V. parahaemolyticus possesses two TTSS, each of which delivers an exclusive set of effectors and mediates unique effects on the host cell. TTSS effectors primarily target and alter the activation status of host cell signaling proteins, thereby bringing about changes in the regulation of cellular behavior. TTSS1 is responsible for the cytotoxicity of V. parahaemolyticus, while TTSS2 is necessary for the enterotoxicity of the pathogen. Recent publications have elucidated the function of several TTSS effectors and their importance in the virulence of the bacterium. This review will explore the ability of the TTSS to manipulate activities of human intestinal cells and how this modification of cell function favors bacterial colonization and persistence of V. parahaemolyticus in the host.

AphA is required for biofilm formation, motility, and virulence in pandemic Vibrio parahaemolyticus

AphA is a small PadR-family DNA-binding regulator in vibrios. AphA has been shown to be involved in transcriptional auto-repression, intestinal colonization and lethality in mice, biofilm formation, and quorum sensing in Vibrio cholerae. The AphA protein of Vibrio parahaemolyticus has 85% identity to that of V. cholerae with the same number of amino acids. In this work, the aphA null mutant was constructed from a wild-type pandemic strain of V. parahaemolyticus for characterization of the phenotypic changes. AphA is required for biofilm formation in V. parahaemolyticus, and a decreased production of biofilm exopolysaccharide matrix in the aphA mutant relative to the wild-type parent strain accounts for its reduced biofilm formation. AphA is also necessary for the optimal swimming and swarming motility of V. parahaemolyticus. In addition, AphA is essential for lethality in mice and cytotoxic activity, but the aphA deletion did not have effect on enterotoxicity.

Characterization of the type III secretion associated low calcium response genes of Vibrio parahaemolyticus RIMD2210633

Vibrio parahaemolyticus is a significant human pathogen associated with gastroenteritis. Two V. parahaemolyticus type 3 secretion systems, T3SS-1 and T3SS-2, secrete effector proteins and have been implicated in host-cell cytotoxicity and enterotoxicity, respectively. Vibrio parahaemolyticus T3SS-1 substrates have been identified, although many predicted substrates (based on homologies) remain undetected in secreted fractions and therefore uncharacterized. We have experimentally developed and optimized a secretion assay protocol allowing for reliable and reproducible detection of V. parahaemolyticus T3SS-1 secreted proteins within culture supernatants. The presence of magnesium and absence of calcium were critical factors in promoting type III secretion of protein substrates. Proteomic approaches identified known V. parahaemolyticus secreted effectors in addition to previously unidentified proteins. Isogenic mutants in putative low calcium response genes were generated, and experiments further implicated the genes in secretion and V. parahaemolyticus-mediated host-cell cytotoxicity during infection. These approaches should be valuable towards future detailed genetic and biochemical analyses of T3SS-1 in V. parahaemolyticus.

Molecular characterization of direct target genes and cis-acting consensus recognized by quorum-sensing regulator AphA in Vibrio parahaemolyticus

BACKGROUND

AphA is the master quorum-sensing (QS) regulator operating at low cell density in vibrios. Molecular regulation of target genes by AphA has been characterized in Vibrio harveyi and V. cholerae, but it is still poorly understood in V. parahaemolyticus.

METHODOLOGY/PRINCIPAL FINDINGS

The AphA proteins are extremely conserved in V. parahaemolyticus, Vibrio sp. Ex25, Vibrio sp. EJY3, V. harveyi, V. vulnificus, V. splendidus, V. anguillarum, V. cholerae, and V. furnissii. The above nine AphA orthologs appear to recognize conserved cis-acting DNA signals which can be represented by two consensus constructs, a 20 bp box sequence and a position frequency matrix. V. parahaemolyticus AphA represses the transcription of ahpA, qrr4, and opaR through direct AphA-target promoter DNA association, while it inhibits the qrr2-3 transcription in an indirect manner. Translation and transcription starts, core promoter elements for sigma factor recognition, Shine-Dalgarno sequences for ribosome recognition, and AphA-binding sites (containing corresponding AphA box-like sequences) were determined for the three direct AphA targets ahpA, qrr4, and opaR in V. parahaemolyticus.

CONCLUSIONS/SIGNIFICANCE

AphA-mediated repression of ahpA, qrr2-4, and opaR was characterized in V. parahaemolyticus by using multiple biochemical and molecular experiments. The computational promoter analysis indicated the conserved mechanism of transcriptional regulation of QS regulator-encoding genes ahpA, qrr4, and opaR in vibrios.

Vibrio parahaemolyticus ExsE is requisite for initial adhesion and subsequent type III secretion system 1-dependent autophagy in HeLa cells

Vibrio parahaemolyticus pandemic serotype O3 : K6 causes acute gastroenteritis, wound infections and septicaemia in humans. This organism encodes two type III secretion systems (T3SS1 and T3SS2); host-cell cytotoxicity has been attributed to T3SS1. Synthesis and secretion of T3SS1 proteins is positively regulated by ExsA, which is presumptively regulated by the ExsCDE pathway, similar to Pseudomonas aeruginosa. Herein we deleted the putative exsE from V. parahaemolyticus and found constitutive expression of the T3SS1 in broth culture as expected. More importantly, however, in a cell culture model, the ΔexsE strain was unable to induce cytotoxicity, as measured by release of lactate dehydrogenase (LDH), or autophagy, as measured by LC3 conversion. This is markedly different from P. aeruginosa, where deletion of exsE has no effect on host-cell cytolysis. Swarming and cytoadhesion were reduced for the deletion mutant and could be recovered along with T3SS1-induced HeLa cell cytotoxicity by in cis expression of exsE in the ΔexsE strain. Loss of adhesion and swarming motility was associated with the loss of flagella biogenesis in the exsE-deficient strain. Mouse mortality was unaffected by the deletion of exsE compared with a wild-type control, suggesting that additional adhesins are important for intoxication in vivo. Based on these data, we conclude that ExsE contributes to the negative regulation of T3SS1 and, in addition, contributes to regulation of an adherence phenotype that is requisite for translocation of effector proteins into HeLa cells.

Transcriptional regulation of opaR, qrr2-4 and aphA by the master quorum-sensing regulator OpaR in Vibrio parahaemolyticus

Background

Vibrio parahaemolyticus is a leading cause of infectious diarrhea and enterogastritis via the fecal-oral route. V. harveyi is a pathogen of fishes and invertebrates, and has been used as a model for quorum sensing (QS) studies. LuxR is the master QS regulator (MQSR) of V. harveyi, and LuxR-dependent expression of its own gene, qrr2–4 and aphA have been established in V. harveyi. Molecular regulation of target genes by the V. parahaemolyticus MQSR OpaR is still poorly understood.

Methodology/Principal Findings

The bioinformatics analysis indicated that V. parahaemolyticus OpaR, V. harveyi LuxR, V. vulnificu SmcR, and V. alginolyticus ValR were extremely conserved, and that these four MQSRs appeared to recognize the same conserved cis-acting signals, which was represented by the consensus constructs manifesting as a position frequency matrix and as a 20 bp box, within their target promoters. The MQSR box-like sequences were found within the upstream DNA regions of opaR, qrr2–4 and aphA in V. parahaemolyticus, and the direct transcriptional regulation of these target genes by OpaR were further confirmed by multiple biochemical experiments including primer extension assay, gel mobility shift assay, and DNase I footprinting analysis. Translation and transcription starts, core promoter elements for sigma factor recognition, Shine-Dalgarno sequences for ribosome recognition, and OpaR-binding sites were determined for the five target genes of OpaR, which gave a structural map of the OpaR-dependent promoters. Further computational promoter analysis indicated the above regulatory circuits were shared by several other closely related Vibrios but with slight exceptions.

Conclusions/Significance

This study gave a comprehensive computational and characterization of the direct transcriptional regulation of five target genes, opaR, qrr2–4 and ahpA, by OpaR in V. parahaemolyticus. These characterized regulatory circuits were conserved in V. harveyi and V. parahaemolyticus.

Bacteria and host interactions in the gut epithelial barrier

The gut mucosa acts as a barrier against microbial invaders, whereas resident commensal and foreign invading bacteria interact intimately with the gut epithelium and influence the host cellular and immune systems. The epithelial barrier serves as an infectious foothold for many bacterial pathogens and as an entry port for pathogens to disseminate into deeper tissues. Enteric bacterial pathogens can efficiently infect the gut mucosa using highly sophisticated virulence mechanisms that allow bacteria to circumvent the defense barriers in the gut. We provide an overview of the components of the mucosal barrier and discuss the bacterial stratagems that circumvent these barriers with particular emphasis on the roles of bacterial effector proteins.

Manipulation of host membranes by bacterial effectors

Bacterial pathogens interact with host membranes to trigger a wide range of cellular processes during the course of infection. These processes include alterations to the dynamics between the plasma membrane and the actin cytoskeleton, and subversion of the membrane-associated pathways involved in vesicle trafficking. Such changes facilitate the entry and replication of the pathogen, and prevent its phagocytosis and degradation. In this Review, we describe the manipulation of host membranes by numerous bacterial effectors that target phosphoinositide metabolism, GTPase signalling and autophagy.

Bacterial protein toxins that modify host regulatory GTPases

Many bacterial pathogens produce protein toxins to outmanoeuvre the immune system of the host. Some of these proteins target regulatory GTPases such as those belonging to the RHO family, which control the actin cytoskeleton of the host cell. In this Review, I discuss a diversity of mechanisms that are used by bacterial effectors and toxins to modulate the activity of host GTPases, with a focus on covalent modifications such as ADP-ribosylation, glucosylation, adenylylation, proteolysis, deamidation and transglutamination.

Adenylylation: renaissance of a forgotten post-translational modification

The stable post-translational modification of proteins by adenylylation or uridylylation was discovered more than four decades ago as a mechanism to regulate the activity of enzymes. Although many other processes involving the covalent transfer of an AMP residue to an amino acid side chain have been identified since then, these are transient adenylylation events that essentially use the free energy of ATP hydrolysis to activate specific processes. Recently, new examples of stable adenylylation of small GTPases involved in signal transduction and regulation of cellular events were discovered, which appear to modulate downstream processes such as cytoskeletal rearrangement and vesicular trafficking. We present a survey of the historical and modern phases of research in this area, focusing on the common and differing aspects of protein adenylylation.

Transcription of Vibrio parahaemolyticus T3SS1 genes is regulated by a dual regulation system consisting of the ExsACDE regulatory cascade and H-NS

Vibrio parahaemolyticus, one of the human pathogenic vibrios, causes gastroenteritis, wound infections and septicemia. Genomic sequencing of this organism revealed that it has two distinct type III secretion systems (T3SS1 and T3SS2). T3SS1 plays a significant role in lethal activity in a murine infection model. It was reported that expression of the T3SS1 gene is controlled by a positive regulator, ExsA, and a negative regulator, ExsD, which share a degree of sequence similarity with Pseudomonas aeruginosa ExsA and ExsD, respectively. However, it is unknown whether T3SS1 is regulated by a mechanism similar to that demonstrated for P. aeruginosa, because functional analysis of VP1701, which is homologous to ExsC, is lacking and there is no ExsE homologue in the T3SS1 region. Here, we demonstrate that vp1701 and vp1702 are functional orthologues of exsC and exsE, respectively, of P. aeruginosa. VP1701 was required for the production of T3SS1-related proteins. VP1702 was a negative regulator for T3SS1-related protein production and was secreted by T3SS1. We also found that H-NS represses T3SS1-related gene expression by suppressing exsA gene expression. These findings indicate that the transcription of V. parahaemolyticus T3SS1 genes is regulated by a dual regulatory system consisting of the ExsACDE regulatory cascade and H-NS.

Regulation of type III secretion system 1 gene expression in Vibrio parahaemolyticus is dependent on interactions between ExsA, ExsC, and ExsD

Vibrio parahaemolyticus ExsA is the transcriptional regulator for type III secretion system 1 (T3SS1) while ExsD blocks T3SS1 expression. Herein we show that deletion of exsC from V. parahaemolyticus blocked synthesis of T3SS1-dependent proteins under inducing conditions (contact with HeLa cells), while in trans complementation of the ΔexsC strain with wild-type exsC restored protein synthesis. Under non-inducing conditions (Luria broth plus salt), in trans expression of exsC in a wild-type strain resulted in synthesis and secretion of T3SS1-dependent proteins. Deletion of exsC does not affect the synthesis of ExsA while expression of T3SS1 genes is independent of ExsC in the absence of ExsD. Co-expression of recombinant proteins with different antigenic tags demonstrated that ExsC binds ExsD and that the N-terminal amino acids of ExsC (positions 7 to 12) are required for binding. Co-expression and purification of antigentically tagged ExsA and ExsD demonstrated that ExsD directly binds ExsA and presumably prevents ExsA from binding promoter regions of T3SS1 genes. Collectively these data demonstrate that ExsD binds ExsA to block expression of T3SS1 genes, while ExsC binds ExsD to permit expression of T3SS1 genes. ExsA, ExsC, and ExsD from V. parahaemolyticus appear to be functional orthologues of their Pseudomonas aeruginosa counterparts.

Kinetic and structural insights into the mechanism of AMPylation by VopS Fic domain

The bacterial pathogen Vibrio parahemeolyticus manipulates host signaling pathways during infections by injecting type III effectors into the cytoplasm of the target cell. One of these effectors, VopS, blocks actin assembly by AMPylation of a conserved threonine residue in the switch 1 region of Rho GTPases. The modified GTPases are no longer able to interact with downstream effectors due to steric hindrance by the covalently linked AMP moiety. Herein we analyze the structure of VopS and its evolutionarily conserved catalytic residues. Steady-state analysis of VopS mutants provides kinetic understanding on the functional role of each residue for AMPylation activity by the Fic domain. Further mechanistic analysis of VopS with its two substrates, ATP and Cdc42, demonstrates that VopS utilizes a sequential mechanism to AMPylate Rho GTPases. Discovery of a ternary reaction mechanism along with structural insight provides critical groundwork for future studies for the family of AMPylators that modify hydroxyl-containing residues with AMP.

Vibrio VopQ induces PI3-kinase-independent autophagy and antagonizes phagocytosis

Vibrio parahaemolyticus is a Gram-negative bacterium responsible for gastroenteritis acquired from the consumption of contaminated shellfish. This bacterium harbours two type III secretion systems, one on each chromosome. The type III secretion system on chromosome I induces cell death by a temporally controlled sequence of events that is caspase-independent and first involves induction of autophagy, followed by cellular rounding, and finally cellular lysis. VopQ is a type III secreted effector that is necessary for the induction of autophagy as mutant strains lacking VopQ are attenuated in their ability to induce autophagy during infection. VopQ is sufficient to induce rapid autophagy as demonstrated by microinjection of recombinant VopQ into GFP-LC3 HeLa cells. Our results demonstrate that VopQ is both necessary and sufficient for induction of autophagy during V. parahaemolyticus-mediated cell death and this effect is independent of phosphatidylinositol-3-kinases but requires Atg5. Furthermore, induction of VopQ-mediated autophagy prevents recruitment of the necessary cellular machinery required for phagocytosis of V. parahaemolyticus during infection. These data provide important insights into the mechanism used by V. parahaemolyticus to cause disease.

Not without cause: Vibrio parahaemolyticus induces acute autophagy and cell death

Vibrio parahaemolyticus (V. parahaemolyticus) is a gram-negative halophillic bacterium that causes worldwide seafood-borne gastroenteritis. The prevalence of V. parahaemolyticus in the environment and incidence of infection have been linked to rising water temperatures caused by global warming. Among its virulence factors, V. parahaemolyticus harbors two type III secretion systems (T3SS). Recently, we have shown that T3SS1 induces rapid cellular death that initiates with acute autophagy, as measured by LC3 lipidation and accumulation of early autophagosomal vesicles. While not the first characterized pathogen to usurp autophagy, this is the first example of an extracellular pathogen that exploits this pathway for its own benefit. Here we discuss possible roles for the induction of autophagy during infection and discuss how V. parahaemolyticus-induced autophagy provides insight into key regulatory steps that govern the decision between apoptosis and autophagy.

AMPylation of Rho GTPases by Vibrio VopS disrupts effector binding and downstream signaling

The Vibrio parahaemolyticus type III effector VopS is implicated in cell rounding and the collapse of the actin cytoskeleton by inhibiting Rho guanosine triphosphatases (GTPases). We found that VopS could act to covalently modify a conserved threonine residue on Rho, Rac, and Cdc42 with adenosine 5'-monophosphate (AMP). The resulting AMPylation prevented the interaction of Rho GTPases with downstream effectors, thereby inhibiting actin assembly in the infected cell. Eukaryotic proteins were also directly modified with AMP, potentially expanding the repertoire of posttranslational modifications for molecular signaling.