The regulatory network of Vibrio parahaemolyticus type VI secretion system 1

Bile acids activate the antibacterial T6SS1 in the gut pathogen Vibrio parahaemolyticus

The marine bacterium Vibrio parahaemolyticus is a major cause of seafood-borne gastroenteritis in humans and of acute hepatopancreatic necrosis disease in shrimp. Bile acids, produced by the host and modified into secondary bile acids by commensal bacteria in the gastrointestinal tract, induce the virulence factors leading to disease in humans and shrimp. Here, we show that secondary bile acids also activate this pathogen's type VI secretion system 1, a toxin delivery apparatus mediating interbacterial competition. This finding implies that Vibrio parahaemolyticus exploits secondary bile acids to activate its virulence factors and identify the presence of commensal bacteria that it needs to outcompete in order to colonize the host.IMPORTANCEBacterial pathogens often manipulate their host and cause disease by secreting toxic proteins. However, to successfully colonize a host, they must also remove commensal bacteria that reside in it and may compete with them over resources. Here, we find that the same host-derived molecules that activate the secreted virulence toxins in a gut bacterial pathogen, Vibrio parahaemolyticus, also activate an antibacterial toxin delivery system that targets such commensal bacteria. These findings suggest that a pathogen can use one cue to launch a coordinated, trans-kingdom attack that enables it to colonize a host.

Unveiling the positive impact of biofloc culture on Vibrio parahaemolyticus infection of Pacific white shrimp by reducing quorum sensing and virulence gene expression and enhancing immunity

This study aimed to evaluate and unveil the positive impact of biofloc culture on Vibrio parahaemolyticus infection of Pacific white shrimp by reducing quorum sensing (QS) and virulence gene expression and enhancing shrimp's immunity. The shrimp with an average body weight of 0.50 ± 0.09 g were reared in containers with a volume of 2.5 L, 21 units, and a density of 20 shrimp L-1. The shrimp were cultured for 5 days, with each treatment including biofloc system maintenance with a C/N ratio of 10 and a control treatment without biofloc, followed by a challenge test through immersion using V. parahaemolyticus at densities of 103, 105, and 107 CFU mL-1 initially. The results of the in vitro experiment showed that biofloc suspension can inhibit and disperse biofilm formation, as well as reduce the exo-enzyme activity (amylase, protease, and chitinase) of V. parahaemolyticus. Furthermore, the biofloc treatment significantly reduced the expression of the QS regulatory gene OpaR, the PirB toxin gene, and the virulence factor genes T6SS1 and T6SS2 in both in vitro and in vivo. The biofloc system also increased the expression of shrimp immunity-related genes (LGBP, proPO, SP, and PE) and the survival rate of white shrimp challenged with V. parahaemolyticus.

Type 1 fimbriae-mediated collective protection against type 6 secretion system attacks

Bacterial competition may rely on secretion systems such as the type 6 secretion system (T6SS), which punctures and releases toxic molecules into neighboring cells. To subsist, bacterial targets must counteract the threats posed by T6SS-positive competitors. In this study, we used a comprehensive genome-wide high-throughput screening approach to investigate the dynamics of interbacterial competition. Our primary goal was to identify deletion mutants within the well-characterized E. coli K-12 single-gene deletion library, the Keio collection, that demonstrated resistance to T6SS-mediated killing by the enteropathogenic bacterium Cronobacter malonaticus. We identified 49 potential mutants conferring resistance to T6SS and focused our interest on a deletion mutant (∆fimE) exhibiting enhanced expression of type 1 fimbriae. We demonstrated that the presence of type 1 fimbriae leads to the formation of microcolonies and thus protects against T6SS-mediated assaults. Collectively, our study demonstrated that adhesive structures such as type 1 fimbriae confer collective protective behavior against T6SS attacks.IMPORTANCEType 6 secretion systems (T6SS) are molecular weapons employed by gram-negative bacteria to eliminate neighboring microbes. T6SS plays a pivotal role as a virulence factor, enabling pathogenic gram-negative bacteria to compete with the established communities to colonize hosts and induce infections. Gaining a deeper understanding of bacterial interactions will allow the development of strategies to control the action of systems such as the T6SS that can manipulate bacterial communities. In this context, we demonstrate that bacteria targeted by T6SS attacks from the enteric pathogen Cronobacter malonaticus, which poses a significant threat to infants, can develop a collective protective mechanism centered on the production of type I fimbriae. These adhesive structures promote the aggregation of bacterial preys and the formation of microcolonies, which protect the cells from T6SS attacks.

Validation of the Thermo Scientific™ SureTect™ Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus PCR Assay for the Detection of Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus in Seafood Matrixes: AOAC Performance Tested MethodsSM 022301

BACKGROUND

The Thermo Scientific™ SureTect™ Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus PCR Assay method is a real-time PCR method for the multiplex detection of Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus in seafood.

OBJECTIVE

The Thermo Scientific SureTect Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus Assay was evaluated for AOAC Performance Tested MethodsSM certification.

METHOD

Inclusivity/exclusivity, matrix, product consistency/stability, and robustness studies were conducted to assess the method's performance. For the matrix study, the method was validated using the Applied Biosystems™ QuantStudio™ 5 Real-Time PCR Food Safety Instrument and the Applied Biosystems™ 7500 Fast Real-Time PCR Food Safety Instrument against the U.S. Food and Drug Administration Bacteriological Analytical Manual, Chapter 9 (2004), Vibrio and ISO 21872-1:2017 Microbiology of the food chain-Horizontal method for the determination of Vibrio spp.-Part 1: Detection of potentially enteropathogenic Vibrio parahaemolyticus, Vibrio cholerae, and Vibrio vulnificus reference methods.

RESULTS

Matrix studies showed equivalent or superior performance of the candidate method compared to the reference method and, overall, no difference between presumptive and confirmed results, except for one matrix due to high background flora. The inclusivity/exclusivity study correctly identified/excluded all strains analyzed. Robustness testing showed no statistically significant differences in assay performance under varied test conditions. Product consistency and stability studies demonstrated no statistically significant differences between assay lots with different expiration dates.

CONCLUSIONS

The data presented show that the assay constitutes a rapid and reliable workflow for the detection of V. cholerae, V. parahaemolyticus, and V. vulnificus in seafood matrixes.

HIGHLIGHTS

The SureTect PCR Assay method allows for fast, reliable detection of stipulated strains in seafood matrixes with results obtained in as little as 80 min post-enrichment.

Regulation of type VI secretion systems at the transcriptional, posttranscriptional and posttranslational level

Bacteria live in complex polymicrobial communities and are constantly competing for resources. The type VI secretion system (T6SS) is a widespread antagonistic mechanism used by Gram-negative bacteria to gain an advantage over competitors. T6SSs translocate toxic effector proteins inside target prokaryotic cells in a contact-dependent manner. In addition, some T6SS effectors can be secreted extracellularly and contribute to the scavenging scarce metal ions. Bacteria deploy their T6SSs in different situations, categorizing these systems into offensive, defensive and exploitative. The great variety of bacterial species and environments occupied by such species reflect the complexity of regulatory signals and networks that control the expression and activation of the T6SSs. Such regulation is tightly controlled at the transcriptional, posttranscriptional and posttranslational level by abiotic (e.g. pH, iron) or biotic (e.g. quorum-sensing) cues. In this review, we provide an update on the current knowledge about the regulatory networks that modulate the expression and activity of T6SSs across several species, focusing on systems used for interbacterial competition.

Sporadic type VI secretion in seventh pandemic Vibrio cholerae

Vibrio cholerae is a pathogen that causes disease in millions of people every year by colonizing the small intestine and then secreting the potent cholera toxin. How the pathogen overcomes the colonization barrier created by the host's natural microbiota is, however, still not well understood. In this context, the type VI secretion system (T6SS) has gained considerable attention given its ability to mediate interbacterial killing. Interestingly, and in contrast to non-pandemic or environmental V. cholerae isolates, strains that are causing the ongoing cholera pandemic (7PET clade) are considered T6SS-silent under laboratory conditions. Since this idea was recently challenged, we performed a comparative in vitro study on T6SS activity using diverse strains or regulatory mutants. We show that modest T6SS activity is detectable in most of the tested strains under interbacterial competition conditions. The system's activity was also observed through immunodetection of the T6SS tube protein Hcp in culture supernatants, a phenotype that can be masked by the strains' haemagglutinin/protease. We further investigated the low T6SS activity within the bacterial populations by imaging 7PET V. cholerae at the single-cell level. The micrographs showed the production of the machinery in only a small fraction of cells within the population. This sporadic T6SS production was higher at 30 °C than at 37 °C and occurred independently of the known regulators TfoX and TfoY but was dependent on the VxrAB two-component system. Overall, our work provides new insight into the heterogeneity of T6SS production in populations of 7PET V. cholerae strains in vitro and provides a possible explanation of the system's low activity in bulk measurements.

Characterization of the RpoN regulon reveals the regulation of motility, T6SS2 and metabolism in Vibrio parahaemolyticus

Vibrio parahaemolyticus is a foodborne pathogen that can colonize the small intestine of the host and cause diarrhea. The alternative sigma factor RpoN plays a vital role in regulating motility, carbon utilization and affects host colonization in V. parahaemolyticus RIMD2210633. In this study, transcriptome and phenotypic analysis further expanded our understanding of the RpoN regulon in V. parahaemolyticus. A deletion mutant of rpoN (ΔrpoN) was subjected to RNA-seq for systemic identification of the RpoN-controlled genes. Compared with the wild-type (WT), 399 genes were differentially expressed in the ΔrpoN strain. Moreover, 264 genes were down-regulated in the ΔrpoN strain, including those associated with nitrogen utilization (VP0118), glutamine synthetase (VP0121), formate dehydrogenase (VP1511 and VP1513-VP1515), quorum sensing (opaR and luxZ), polar flagellar systems, and type VI secretion system 2 (T6SS2). Quantitative real-time reverse transcription PCR (qRT-PCR) and electrophoretic mobility shift assay (EMSA) further confirmed that RpoN could directly bind to the promoters of these genes associated with polar flagellar systems (flgB and fliE), lateral flagellar systems (flgB2 and lafA), T6SS2 (hcp2 and VPA1044) and glutamine synthetase (VP0121), and then positively regulate the expression of these systems. A RpoN-binding motif was identified in V. parahaemolyticus using the MEME suite and verified by the EMSA. Besides, the deletion of rpoN caused a significant decrease in hemolytic activity, adhesion, and cytotoxicity. Our results provide new cues to better understand the regulatory networks of RpoN protein to motility, T6SS2, and metabolism in V. parahaemolyticus.

Single nucleotide polymorphism determines constitutive versus inducible type VI secretion in Vibrio cholerae

Vibrio cholerae is a well-studied human pathogen that is also a common inhabitant of marine habitats. In both environments, the bacterium is subject to interbacterial competition. A molecular nanomachine that is often involved in such competitive behavior is the type VI secretion system (T6SS). Interestingly and in contrast to non-pandemic or environmental isolates, the T6SS of the O1 El Tor clade of V. cholerae, which is responsible for the ongoing 7th cholera pandemic, is largely silent under standard laboratory culture conditions. Instead, these strains induce their full T6SS capacity only under specific conditions such as growth on chitinous surfaces (signaled through TfoX and QstR) or when the cells encounter low intracellular c-di-GMP levels (TfoY-driven). In this study, we identified a single nucleotide polymorphism (SNP) within an intergenic region of the major T6SS gene cluster of V. cholerae that determines the T6SS status of the cell. We show that SNP conversion is sufficient to induce T6SS production in numerous pandemic strains, while the converse approach renders non-pandemic/environmental V. cholerae strains T6SS-silent. We further demonstrate that SNP-dependent T6SS production occurs independently of the known T6SS regulators TfoX, QstR, and TfoY. Finally, we identify a putative promoter region adjacent to the identified SNP that is required for all forms of T6SS regulation in V. cholerae.

A Novel Transcription Factor VPA0041 Was Identified to Regulate the Swarming Motility in Vibrio parahaemolyticus

Vibrio parahaemolyticus can change their usual lifestyle of surviving in an aqueous environment attached to a host, wherein both swimming motility and swarming motility play important roles in lifestyle changes, respectively. VPA0041 is a novel transcription factor involved in regulating the swarming ability of V. parahaemolyticus. The deletion of the vpa0041 gene resulted in the loss of swarming motility in the brain heart infusion (BHI) agars, while the swimming motility was unaffected by VPA0041. Transmission electron microscope (TEM) assays showed that no flagellum was found around the bacterial cells. RNA-sequencing (RNA-Seq) analysis revealed that VPA0041 regulated 315 genes; 207 genes were up-regulated, and 108 genes were down-regulated. RNA-seq results indicated that the lateral flagellar genes were down-regulated by VPA0041, which was confirmed by real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Electrophoretic mobility shift assays (EMSA) demonstrated that VPA0041 directly bound to the promoters of vpa0264, vpa1548, and vpa1550 to regulate the expression of the lateral flagellar genes. Our results demonstrated that the transcription factor VPA0041 could directly regulate the expression of lateral flagellar genes to mediate the swarming motility in V. parahaemolyticus.

Genetic Basis of High-Pressure Tolerance of a Vibrio parahaemolyticus Mutant and Its Pathogenicity

Foodborne pathogens with high-pressure processing (HPP) tolerance and their pathogenicity have gained considerable attention in the field of food safety. However, tolerance to pressure treatment varies among microorganisms and growth phases, and the mechanism by which Vibrio parahaemolyticus can become tolerant of HPP is currently not known. In this study, 183 strains of V. parahaemolyticus were isolated from seafood products, and one strain, C4, carried a thermostable direct hemolysin (tdh) gene. A strain, N11, which was acquired from the C4 strain through adaptive laboratory evolution under HPP stress, could tolerate up to 200 MPa for 10 min. Compared with the C4 strain, the catalase and Na⁺/K⁺-ATPase activities in N11 strain were increased by about 2–3 times, and the cells maintained an intact cell membrane structure under HPP treatment. As shown by murine infection trials, the C4 and N11 strains impacted the physiological activities of mice and damaged liver and spleen cells. Comparative genomic analysis showed that 19 nucleotides were mutated in the N11 strain, which led to sustained high expression of mlaC and mlaD genes in this strain. Knockout of these genes confirmed that they were involved in the high-pressure stress response, and also related to pathogenicity of V. parahaemolyticus. Thereby, our findings revealed a HPP tolerance mechanism of V. parahaemolyticus, and the high-pressure-tolerant strain still retained pathogenicity in mice with skin and fur pleating and lethargy, indicating the pressure-tolerant foodborne pathogens present health risks.

A Rapid Fluorescence-Based Screen to Identify Regulators and Components of Interbacterial Competition Mechanisms in Bacteria

Contact-dependent antibacterial mechanisms enhance bacterial fitness as they enable bacteria to outcompete their rivals and thrive in diverse environments. Such systems also allow pathogenic bacteria to establish a niche inside a host, where they must compete with commensal microflora. In many cases, antibacterial systems are tightly regulated by complex sensor and signal transduction networks. Deciphering these regulatory networks, as well as identifying functional components of antibacterial mechanisms, are valuable objectives since essential regulators and components present possible targets for developing antivirulence therapies. Here we describe Bacterial Competition Fluorescence (BaCoF), a methodology that relies on a fluorescence signal to determine the outcome of bacterial competitions. This methodology enables screening of mutant libraries to identify genes that are essential for activating a contact-dependent antibacterial system of interest. Thus, this methodology can be applied to reveal essential regulators and components of antibacterial systems in bacterial pathogens.

Rapid detection of Vibrio parahaemolyticus using magnetic nanobead-based immunoseparation and quantum dot-based immunofluorescence

In recent years, the scale of population exposure and food poisoning caused by Vibrio parahaemolyticus (V. parahaemolyticus) has shown a significant upward trend, becoming one of the primary food-borne pathogens. Herein, we developed a rapid and sensitive detection of V. parahaemolyticus by integrating the technology of magnetic nanobeads (MBs) based immunoseparation (IMS) with quantum dots (QDs) based immunofluorescence. Firstly, specific rabbit polyclone IgG antibodies (IgG) and chicken egg yolk antibodies (IgY) of V. parahaemolyticus were prepared. Then two sizes of MBs (1 μm; 180 nm) were coupled with IgG to form immuno-MB (IMB) capture probes for evaluating the effect of different sizes on the detection efficiency. For QDs, they were conjugated with IgY to form fluorescent reporting probes. In the process of detection, IMB probes were used to separate V. parahaemolyticus and then these complexes were labeled by QD probes on the principle of double antibody sandwich. The fluorescence intensity of the IMB-V. parahaemolyticus-QD complexes was measured by a fluorescence spectrophotometer. The detection method takes 150 min with a detection limit of 102 cfu mL-1 ranging from 102 to 106 cfu mL-1 and it has been shown to work satisfactorily in real food samples.

Engineering a customizable antibacterial T6SS-based platform in Vibrio natriegens

Bacterial pathogens are a major risk to human, animal, and plant health. To counteract the spread of antibiotic resistance, alternative antibacterial strategies are urgently needed. Here, we construct a proof‐of‐concept customizable, modular, and inducible antibacterial toxin delivery platform. By engineering a type VI secretion system (T6SS) that is controlled by an externally induced on/off switch, we transform the safe bacterium, Vibrio natriegens, into an effective antibacterial weapon. Furthermore, we demonstrate that the delivered effector repertoire, and thus the toxicity range of this platform, can be easily manipulated and tested. We believe that this platform can serve as a foundation for novel antibacterial bio‐treatments, as well as a unique tool to study antibacterial toxins.

Adaptations of Vibrio parahaemolyticus to Stress During Environmental Survival, Host Colonization, and Infection

Vibrio parahaemolyticus (Vp) is an aquatic Gram-negative bacterium that may infect humans and cause gastroenteritis and wound infections. The first pandemic of Vp associated infection was caused by the serovar O3:K6 and epidemics caused by the other serovars are increasingly reported. The two major virulence factors, thermostable direct hemolysin (TDH) and/or TDH-related hemolysin (TRH), are associated with hemolysis and cytotoxicity. Vp strains lacking tdh and/or trh are avirulent and able to colonize in the human gut and cause infection using other unknown factors. This pathogen is well adapted to survive in the environment and human host using several genetic mechanisms. The presence of prophages in Vp contributes to the emergence of pathogenic strains from the marine environment. Vp has two putative type-III and type-VI secretion systems (T3SS and T6SS, respectively) located on both the chromosomes. T3SS play a crucial role during the infection process by causing cytotoxicity and enterotoxicity. T6SS contribute to adhesion, virulence associated with interbacterial competition in the gut milieu. Due to differential expression, type III secretion system 2 (encoded on chromosome-2, T3SS2) and other genes are activated and transcribed by interaction with bile salts within the host. Chromosome-1 encoded T6SS1 has been predominantly identified in clinical isolates. Acquisition of genomic islands by horizontal gene transfer provides enhanced tolerance of Vp toward several antibiotics and heavy metals. Vp consists of evolutionarily conserved targets of GTPases and kinases. Expression of these genes is responsible for the survival of Vp in the host and biochemical changes during its survival. Advanced genomic analysis has revealed that various genes are encoded in Vp pathogenicity island that control and expression of virulence in the host. In the environment, the biofilm gene expression has been positively correlated to tolerance toward aerobic, anaerobic, and micro-aerobic conditions. The genetic similarity analysis of toxin/antitoxin systems of Escherichia coli with VP genome has shown a function that could induce a viable non-culturable state by preventing cell division. A better interpretation of the Vp virulence and other mechanisms that support its environmental fitness are important for diagnosis, treatment, prevention and spread of infections. This review identifies some of the common regulatory pathways of Vp in response to different stresses that influence its survival, gut colonization and virulence.

The transcriptional regulator Zur regulates the expression of ZnuABC and T6SS4 in response to stresses in Yersinia pseudotuberculosis

Zinc homeostasis is crucial for the development and stress resistance of bacteria in the environment. Serial zinc sensing transcriptional regulators, zinc transporters and zinc binding proteins were found to maintain the zinc homeostasis in bacteria. Zur is a zinc uptake regulator that is widely distributed in species, and ZnuABC, as well as the Type VI Secretion System (T6SS4) function in zinc acquisition. Here, we report that the regulator Zur inhibits the expression of the ZnuABC which inhibition could be eliminated at low zinc level, and upregulates the T6SS4 operon in Yersinia pseudotuberculosis to facilitate Zn²⁺ uptake and oxidative stress resistance. Zur regulates the expression of ZnuABC and T6SS4 by directly binding to their promoter regions. Zur senses the Zn²⁺ concentration and represses ZnuABC in a Zn²⁺-containing environment. Zur works as an auxiliary regular activator of T6SS4, facilitating oxidative stress resistance. This study revealed the dual function of regulator Zur on ZnuABC and T6SS4, and enriched the knowledge of Zn²⁺ homeostasis maintenance in Y. pseudotuberculosis.

Role of the Type VI Secretion System in the Pathogenicity of Pseudomonas syringae pv. actinidiae, the Causative Agent of Kiwifruit Bacterial Canker

The type VI secretion system (T6SS), a macromolecular machine, plays an important role in the pathogenicity of many Gram-negative bacteria. However, the role of T6SS in the pathogenicity of Pseudomonas syringae pv. actinidiae (Psa), the pathogen of kiwifruit bacterial canker, is yet to be studied. Here, we found a T6SS gene cluster consisting of 13 core genes (A-J) in the genome of Psa M228 based on a genome-wide analysis. To determine whether the T6SS gene cluster affects the pathogenicity of Psa M228, T6SS and its 13 core gene deletion mutants were constructed and their pathogenicity was determined. The deletion mutants showed different degrees of reduction in pathogenicity compared with the wild-type strain M228; in tssM and tssJ mutants, pathogenicity was significantly reduced by 78.7 and 71.3%, respectively. The pathogenicity results were also confirmed by electron microscopy. To further confirm that the reduction in pathogenicity is related to the function of T6SS, we selected the T6SS gene cluster, comprising tssM and tssJ, for further analyses. Western blot results revealed that tssM and tssJ were necessary for hemolytic co-regulatory protein secretion, indicating that they encode a functional T6SS. Further, we explored the mechanism by which T6SS affects the pathogenicity of Psa M228. The ability of bacterial competition, biofilm formation, hydrogen peroxide tolerance, and proteolytic activity were all weakened in the deletion mutants M228ΔT6SS, M228ΔtssM, and M228ΔtssJ. All these properties of the two gene complementation mutants were restored to the same levels as those of the wild-type strain, M228. Quantitative real-time results showed that during the interaction between the deletion mutant M228ΔT6SS and the host, expression levels of T3SS transcriptional regulatory gene hrpR, structural genes hrpZ, hrcC, hopP1, and effector genes hopH1 and hopM1 were down-regulated at different levels. Taken together, our data provide evidence for the first time that the T6SS plays an important role in the pathogenicity of Psa, probably via effects on bacterial competition, biofilm formation, and environmental adaptability. Moreover, a complicated relationship exists between T6SS and T3SS.

The type VI secretion system 2 of Vibrio parahaemolyticus is regulated by QsvR

The type VI secretion system 2 (T6SS2) gene locus of Vibrio parahaemolyticus is comprised of three operons, VPA1027-1024, VPA1043-1028, and VPA1044-1046. QsvR is a virulence regulator of V. parahaemolyticus. In this study, the regulation of VPA1027, VPA1043 and VPA1044 by QsvR was investigated by primer extension, quantitative real-time PCR, LacZ fusion, electrophoretic mobility shift assay and DNase I footprinting. The results demonstrated that QsvR binds to the promoter-proximal DNA regions of each of these three operons, activating their transcription. T6SS2 was shown to predominately contribute to V. parahaemolyticus adhesion, with qsvR deletion significantly decreasing V. parahaemolyticus adhesion to HeLa cells. Thus, QsvR is not only a positive regulator of T6SS2 gene transcription but also a mediator of V. parahaemolyticus adhesion to host cells.

The substrate-dependent regulatory effects of the AfeI/R system in Acidithiobacillus ferrooxidans reveals the novel regulation strategy of quorum sensing in acidophiles

A LuxI/R‐like quorum sensing (QS) system (AfeI/R) has been reported in the acidophilic and chemoautotrophic Acidithiobacillus spp. However, the function of AfeI/R remains unclear because of the difficulties in the genetic manipulation of these bacteria. Here, we constructed different afeI mutants of the sulfur‐ and iron‐oxidizer A. ferrooxidans, identified the N‐acyl homoserine lactones (acyl‐HSLs) synthesized by AfeI, and determined the regulatory effects of AfeI/R on genes expression, extracellular polymeric substance synthesis, energy metabolism, cell growth and population density of A. ferrooxidans in different energy substrates. Acyl‐HSLs‐mediated distinct regulation strategies were employed to influence bacterial metabolism and cell growth of A. ferrooxidans cultivated in either sulfur or ferrous iron. Based on these findings, an energy‐substrate‐dependent regulation mode of AfeI/R in A. ferrooxidans was illuminated that AfeI/R could produce different types of acyl‐HSLs and employ specific acyl‐HSLs to regulate specific genes in response to different energy substrates. The discovery of the AfeI/R‐mediated substrate‐dependent regulatory mode expands our knowledge on the function of QS system in the chemoautotrophic sulfur‐ and ferrous iron‐oxidizing bacteria, and provides new insights in understanding energy metabolism modulation, population control, bacteria‐driven bioleaching process, and the coevolution between the acidophiles and their acidic habitats.

Comparative Proteomics and Secretomics Revealed Virulence and Antibiotic Resistance-Associated Factors in Vibrio parahaemolyticus Recovered From Commonly Consumed Aquatic Products

Vibrio parahaemolyticus is a seafoodborne pathogen that can cause severe gastroenteritis and septicemia diseases in humans and even death. The emergence of multidrug-resistant V. parahaemolyticus leads to difficulties and rising costs of medical treatment. The bacterium of environmental origins containing no major virulence genes (tdh and trh) has been reported to be associated with infectious diarrhea disease as well. Identification of risk factors in V. parahaemolyticus is imperative for assuming food safety. In this study, we obtained secretomic and proteomic profiles of V. parahaemolyticus isolated from 12 species of commonly consumed aquatic products and identified candidate protein spots by using two-dimensional gel electrophoresis and liquid chromatography tandem mass spectrometry techniques. A total of 11 common and 28 differential extracellular proteins were found from distinct secretomic profiles, including eight virulence-associated proteins: outer membrane channel TolC, maltoporin, elongation factor Tu, enolase, transaldolase, flagellin C, polar flagellin B/D, and superoxide dismutase, as well as five antimicrobial and/or heavy metal resistance-associated ABC transporter proteins. Comparison of proteomic profiles derived from the 12 V. parahaemolyticus isolates also revealed five intracellular virulence-related proteins, including aldehyde-alcohol dehydrogenase, outer membrane protein A, alkyl hydroperoxide reductase C, phosphoenolpyruvate-protein phosphotransferase, and phosphoglycerate kinase. Additionally, our data indicated that aquatic product matrices significantly altered proteomic profiles of the V. parahaemolyticus isolates with a number of differentially expressed proteins identified. The results in this study meet the increasing need for novel diagnosis candidates of the leading seafoodborne pathogen worldwide.

A comparative genomics methodology reveals a widespread family of membrane-disrupting T6SS effectors

Gram-negative bacteria deliver effectors via the type VI secretion system (T6SS) to outcompete their rivals. Each bacterial strain carries a different arsenal of effectors; the identities of many remain unknown. Here, we present an approach to identify T6SS effectors encoded in bacterial genomes of interest, without prior knowledge of the effectors’ domain content or genetic neighborhood. Our pipeline comprises a comparative genomics analysis followed by screening using a surrogate T6SS⁺ strain. Using this approach, we identify an antibacterial effector belonging to the T6SS1 of Vibrio parahaemolyticus, representing a widespread family of T6SS effectors sharing a C-terminal domain that we name Tme (Type VI membrane-disrupting effector). Tme effectors function in the periplasm where they intoxicate bacteria by disrupting membrane integrity. We believe our approach can be scaled up to identify additional T6SS effectors in various bacterial genera.

Gram-negative bacteria deliver effectors via the type VI secretion system (T6SS) to outcompete their rivals. Here, Fridman et al. present an approach to identify T6SS effectors encoded in bacterial genomes without prior knowledge of their domain content or genetic neighbourhood, and identify a new family of membrane-disrupting effectors.