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

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

Biofilm formation comparison of Vibrio parahaemolyticus on stainless steel and polypropylene while minimizing environmental impacts and transfer to grouper fish fillets

This study investigated the influence of food contact surface materials on the biofilm formation of Vibrio parahaemolyticus while attempting to minimize the impact of environmental factors. The response surface methodology (RSM), incorporating three controlled environmental factors (temperature, pH, and salinity), was employed to determine the optimal conditions for biofilm formation on stainless steel (SS) and polypropylene (PP) coupons. The RSM results demonstrated that pH was highly influential. After minimizing the impacts of environmental factors, initially V. parahaemolyticus adhered more rapidly on PP than SS. To adhere to SS, V. parahaemolyticus formed extra exopolysaccharide (EPS) and exhibited clustered stacking. Both PP and SS exhibited hydrophilic properties, but SS was more hydrophilic than PP. Finally, this study observed a higher transfer rate of biofilms from PP to fish fillets than from SS to fish fillets. The present findings suggest that the food industry should consider the material of food processing surfaces to prevent V. parahaemolyticus biofilm formation and thus to enhance food safety.

MAM7 from Vibrio parahaemolyticus: Expression, purification and effects on RAW264.7 cells

V. parahaemolyticus is a Gram-negative bacterium that causes gastroenteritis. Within the realm of bacterial interactions with the gut, the outer membrane protein MAM7 plays a key role. However, the precise function of MAM7 in intestinal inflammation, particularly its interactions with macrophages, remains unclear. In this study, we successfully expressed and purified recombinant MAM7. After optimization of the MAM7 expression condition, it was found that the optimal concentration and temperature were 0.75 mM and 15 °C, respectively, resulting in a 27-fold increase in its yield. Furthermore, RAW264.7 cytotoxicity assay was conducted. The CCK-8 results revealed that MAM7 substantially stimulated the proliferation of RAW264.7 cells, with its optimal concentration determined to be 7.5 μg/mL. Following this, the NO concentration of MAM7 was tested, revealing a significant increase (p < 0.05) in NO levels. Additionally, the relative mRNA levels of IL-1β, IL-6, and TNF-α in RAW264.7 cells were measured by qRT-PCR, showing a remarkable elevation (p < 0.05). Moreover, ELISA results demonstrated that MAM7 effectively stimulated the secretion of IL-6 and TNF-α by RAW264.7 cells. In summary, these findings strongly suggest that MAM7 serves as a proinflammatory adhesion factor with the capacity to modulate immune responses.

Polyamide microplastics can mitigate the effects of pathogenic bacterium on the health of marine mussels

Vibrio parahaemolyticus and microplastics are prevalent in the ocean. Bacteria attach onto plastic particles, forming harmful biofilms that collectively threaten bivalve health. This study investigates the interaction between polyamide microplastics (PA: particle size 38 ± 12 µm) and V. parahaemolyticus, as well as their combined impact on thick-shelled mussels (Mytilus coruscus). We introduced 1011 CFU/L of V. parahaemolyticus into varying PA concentrations (0, 5, 50, and 500 particles/L) to observe growth over 14 h and biofilm formation after 48 h. Our findings indicate that microplastics suppress biofilm formation and virulence gene expression. Four treatments were established to monitor mussel responses: a control group without PA or V. parahaemolyticus; a group with 50 particles/L PA; a group with 1011 CFU/L V. parahaemolyticus; and a co-exposure group with both 50 particles/L PA and 1011 CFU/L V. parahaemolyticus, over a 14-day experiment. However, combined stress from microplastics and Vibrio led to immune dysregulation in mussels, resulting in intestinal damage and microbiome disruption. Notably, V. parahaemolyticus had a more severe impact on mussels than microplastics alone, yet their coexistence reduced some harmful effects. This study is the first to explore the interaction between microplastics and V. parahaemolyticus, providing important insights for ecological risk assessments.

Non-cholera Vibrio infections in Southeast Asia: A systematic review and meta-analysis

We reviewed and analyzed the existing data on vibriosis in Southeast Asia to better understand its burden and prevalent causal agents. We searched PubMed, Web of Science, and EMBASE for studies published between January 2000 and April 2024. A random-effects meta-analysis was used to estimate the pooled isolation rate of non-cholera Vibrio species. Among the 1385 retrieved studies, 22 met the inclusion criteria for the systematic review and 11 were included in the meta-analysis. The pooled isolation rate of non-cholera Vibrio species among diarrheal patients was 5.0 %. Most species that caused vibriosis included V. parahaemolyticus, V. mimicus, V. vulnificus, non-O1/non-O139 V. cholerae, V. fluvialis, and V. alginolyticus. Pooled isolation rate of V. parahaemolyticus and non-O1 V. cholerae were 7.0, and 4.0, respectively. The prevalence of vibriosis in Southeast Asia is non-negligible. Public health strategies should prioritize enhanced surveillance, and clinicians should consider vibriosis in diarrheal patients with seafood consumption history.

Vibrio parahaemolyticus Foodborne Illness Associated with Oysters, Australia, 2021-2022

The bacterium Vibrio parahaemolyticus is ubiquitous in tropical and temperate waters throughout the world and causes infections in humans resulting from water exposure and from ingestion of contaminated raw or undercooked seafood, such as oysters. We describe a nationwide outbreak of enteric infections caused by Vibrio parahaemolyticus in Australia during September 2021-January 2022. A total of 268 persons were linked with the outbreak, 97% of whom reported consuming Australia-grown oysters. Cases were reported from all states and territories of Australia. The outbreak comprised 2 distinct strains of V. parahaemolyticus, sequence types 417 and 50. We traced oysters with V. parahaemolyticus proliferation back to a common growing region within the state of South Australia. The outbreak prompted a national recall of oysters and subsequent improvements in postharvest processing of the shellfish.

Sustainable double-synergistic silver-hydroxyapatite composite catalyst derived from fish bones for efficient disinfection of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a food-borne pathogen that poses a serious threat to seafood safety and human health. An efficient, nontoxic, and sustainable disinfection material with a stable structure is urgently needed. Herein, silver (Ag)-hydroxyapatite (HAP) composite catalysts were prepared using HAP derived from waste fish bones. The Ag2.50%-HAP showed a 100% disinfection rate against V. parahaemolyticus, disinfecting nearly 7.0 lg CFU mL-1 within 15 min at a low concentration of 300 μg mL-1. This efficient disinfection activity could be attributed to the double-synergistic effect of Ag and superoxide radicals, which resulted in the destruction of bacterial cell structures and the leakage of intracellular proteins. Importantly, the composite also exhibited high activity in controlling the growth of pathogens during the storage process of Penaeus vannamei. These findings provided sustainable composite catalysts for disinfecting V. parahaemolyticus in seafood and a high-value utilization strategy for waste fish bones.

Insights into the DNA methylation of Portunus trituberculatus in response to Vibrio parahaemolyticus infection

Vibrio parahaemolyticus is the main pathogen causing acute hepatopancreatic necrotic disease in crustaceans. To elucidate the epigenetic regulatory mechanism of crustacean resistance to V. parahaemolyticus infection, we conducted artificial infection studies on Portunus trituberculatus. The results showed that the mortality rate reached the highest at 12 h of artificial infection, which was 23.69 %. At 72 h after V parahaemolyticus infection, the expression level of DNA demethylase (ten-eleven-translocation protein) Tet was significantly decreased, the expression of DNA methyltransferase Dnmt3B fluctuated significantly. Based on the differential expression levels of Tet and Dnmt3B. We depict for DNA methylation profiles of the whole genome of P. trituberculatus at single-base resolution by using whole-genome bisulfite sequencing (WGBS) on hemolymph tissues. The overall DNA methylation level was low at 2.16 % in P. trituberculatus hemolymph. A total of 2590 differentially methylated regions (DMRs) were identified, of which 1329 were hypermethylated and 1261 were hypomethylated, and 1389 genes were annotated in these DMRs. Differently methylated genes (DMGs) were significantly enriched in ribosomes (KO03010), protein kinases (KO01001), cell cycle (HSA04110), endocrine resistance (HSA01522) and FoxO signaling pathway (KO04068). Finally, we selected six differentially methylated genes for quantitative analysis. The results showed that DNA methylation not only has a negative regulatory effect on gene expression, but also has a positive regulatory effect. These results indicated that DNA methylation in the regulation of genes involved in immune responses contributes to the resistance of P. trituberculatus to V. parahaemolyticus, which is valuable for understanding how crustaceans regulate the innate immune system to defend against bacterial infections.

Passive immunoprophylaxis with Ccombodies against Vibrio parahaemolyticus in Pacific white shrimp (Penaeus vannamei)

The Vibrio parahaemolyticus strain causing acute hepatopancreatic necrosis disease (AHPND) in shrimp secretes toxins A and B (PirAVp/PirBVp). These toxins have been implicated in pathogenesis and are targets for developing anti-AHPND therapeutics or prophylactics that include passive immunization. We have previously reported that Ccombodies (recombinant hagfish variable lymphocyte receptor B antibodies; VLRB) targeting PirBVp conferred protection against V. parahaemolyticus in shrimp when administered as a feed supplement. In this study, we screened a phage-displayed library of engineered VLRBs for PirAVp-targeting Ccombodies that were mass-produced in a bacterial expression system. We then introduced these Ccombodies into the diet of Pacific white shrimp (Penaeus vannamei) over a seven-day period. Subsequently, the shrimp were exposed to a challenge with V. parahaemolyticus. Mortality rates were then observed and recorded over the following seven days. Administering shrimp feed supplemented with Ccombodies at a high dose (100 mg per 100 g feed) reduced mortality in recipient animals (2.96-5.19 %) statistically similar to mock-challenged control (1.48 %), but significantly different from the Ccombody-deficient control (74.81 %). This suggests that the Ccombodies provided strong protection against the bacterium. Feeding shrimp with a median dose (10 mg/100 g feed) gave statistically comparable low mortality (5.93-6.67 %) as the high dose. Reducing the Ccombody dose to 1 mg/100 g feed showed variable effects. Ccombody A2 showed mortality (11.85 %) significantly lower than that of the Ccombody-deficient group (74.81 %), suggesting that it can effectively protect against the bacterial challenge at a low dose. Our results demonstrate the ability of the phage-displayed VLRB library to generate antigen-specific Ccombodies rapidly and simply, with the expression of high protein levels in bacteria. The protective effect provided by these Ccombodies aligns with our earlier results, strongly supporting the use of VLRB antibodies as a substitute for IgY in passive immunoprophylaxis against AHPND in shrimp.

Evaluation of the relationships between physico-chemical parameters and the abundance of Vibrio spp. in blue crabs (Callinectes sapidus) and seawater from the Maryland Coastal Bays

Introduction

Fluctuations in water quality characteristics influence the productivity of blue crabs (Callinectes sapidus), and the risk of human exposure to pathogenic Vibrio species. Thus, this study assessed the prevalence of total and pathogenic/clinical markers of Vibrio parahaemolyticus and Vibrio vulnificus in blue crabs and seawater from the Maryland Coastal Bays (MCBs) and the correlation between Vibrio levels and physicochemical parameters.

Methods

Three to five crabs and 1 L of seawater were collected monthly for 3 years (May 2018 to December 2020) from six sites within the MCBs. Hemolymph and crab tissue were extracted and pooled for each site. Extracted hemolymph, crab tissue, and seawater were analyzed for V. parahaemolyticus and V. vulnificus using the Most Probable Number (MPN) and real-time PCR methods. A one-way Analysis of Variance (ANOVA), correlations, and linear models were used to analyze the data. Akaike Information Criterion (AICc) was evaluated to determine the model that provides the best fit to the data relating to Vibrio concentrations and environmental factors.

Results

Results suggested that environmental factors could influence the growth of Vibrio spp. Both V. parahaemolyticus and V. vulnificus were more prevalent during the warmer months than colder months. Vibrio was more prevalent in crab samples compared to seawater. Vibrio vulnificus concentrations in seawater and hemolymph were positively correlated with temperature (p = 0.0143 seawater) and pH (p = 0.006 hemolymph). A negative correlation was observed between the concentration of V. vulnificus in whole crab (tissue) and dissolved oxygen level (p = 0.0256). The concentration of V. parahaemolyticus in seawater was positively correlated with temperature (p = 0.009) and negatively correlated with dissolved oxygen (p = 0.012).

Discussion

These results provide current information on the spatial and temporal distributions of Vibrio spp. in the MCBs that are useful for implementing more efficient processing and handling procedures of seafood products.

Identification, functional analysis of chitin-binding proteins and the association of its single nucleotide polymorphisms with Vibrio parahaemolyticus resistance in Penaeus vannamei

Chitin-binding proteins (CBPs) play pivotal roles in numerous biological processes in arthropods, including growth, molting, reproduction, and immune defense. However, their function in the antibacterial immune defense of crustaceans remains relatively underexplored. In this study, twenty CBPs were identified and characterized in Penaeus vannamei. Expression profiling highlighted that the majority of CBPs were highly expressed in the intestine and hepatopancreas and responded to challenge by Vibrio parahaemolyticus. To explore the role of these CBPs in innate immunity, six CBPs (PvPrg4, PvKrtap16, PvPT-1a, PvPT-1b, PvExtensin and PvCP-AM1159) were selected for RNAi experiments. Silencing of only PvPrg4 and PvKrtap16 significantly decreased the cumulative mortality of V. parahaemolyticus-infected shrimp. Further studies demonstrated that inhibition of PvPrg4 and PvKrtap16 resulted in a marked upregulation of genes associated with the NF-κB and JAK-STAT signaling pathways, as well as antimicrobial peptides (AMPs), in both the intestine and hepatopancreas. These results collectively suggested that PvPrg4 and PvKrtap16 potentially promote V. parahaemolyticus invasion by negatively regulating the JAK-STAT and NF-κB pathways, thereby inhibiting the expression of AMPs. In addition, SNP analysis identified three SNPs in the exons of PvPrg4 that were significantly associated with tolerance to V. parahaemolyticus. Taken together, these findings are expected to assist in the molecular marker-assisted breeding of P. vannamei associated with anti-V. parahaemolyticus traits, as well as expand our understanding of CBP functions within the immune regulatory system of crustaceans.

Evaluation of inhibitory, immunomodulatory, survival, and growth effects of host-derived Weissella confusa on Macrobrachium rosenbergii challenged with Vibrio parahaemolyticus

Macrobrachium rosenbergii is a highly valuable prawn species in aquaculture due to its current growing demand in the market. However, various bacterial diseases caused by Vibrio parahaemolyticus have been observed to induce mortality in larval, juvenile, and adult stages of M. rosenbergii. While antibiotics are commonly used to manage these diseases, they contribute to antimicrobial resistance, a global concern with serious environmental and health implications. Consequently, the scientific community is exploring host-derived beneficial microorganisms as functional feed additives, offering eco-friendly alternatives that boost shrimp and prawn immunity. The purpose of this study was to examine the effects of host-derived beneficial microorganisms from the gut of M. rosenbergii, on the inhibition, immunomodulation, survival, and growth of M. rosenbergii when exposed to V. parahaemolyticus. The result of this study showed that Weissella confusa C6, a lactic acid bacterium isolated from the gut of M. rosenbergii, significantly inhibits the growth of V. parahaemolyticus R1 as demonstrated in agar well diffusion assay and co-culture assay. Additionally, it showed immunomodulatory effects, indicated by elevated total hemocyte count (THC) and phenoloxidase (PO) activity during the bacterial challenge test. Furthermore, supplementing the diet with W. confusa led to significant improvements in M. rosenbergii, including increased survival rates, weight gain, specific growth rate, better feed conversion ratio, and reduced density of V. parahaemolyticus in the prawn's gut. Therefore, it can be considered a viable option for use as a feed supplement in prawn farming, enhancing M. rosenbergii's immune system, disease resistance, and overall health.

PirA- or PirB-binding nanobodies can protect whiteleg shrimp from the acute hepatopancreatic necrosis disease toxin

Acute hepatopancreatic necrosis disease (AHPND) is a devastating shrimp disease caused by a binary toxin, PirAB, produced by Vibrio parahaemolyticus and other closely related bacteria. To address AHPND, over 300 unique single-domain antibodies (also known as nanobodies) derived from the VHH domains of Lama glama heavy-chain-only antibodies were raised against either PirA or PirB and characterized. Nanobodies were shortlisted based on their affinities for either PirA or PirB, their relative stability in intestinal fluids, and their ability to reduce PirAB-induced death in brine shrimp Artemia salina. From these data, a subset of nanobodies was tested for their ability to reduce AHPND in whiteleg shrimp Penaeus vannamei, and nanobodies targeting either PirA or PirB provided significant disease protection to whiteleg shrimp. These results show that nanobodies can be a new option for shrimp farmers to reduce or eliminate the impact of AHPND on their operations.

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.

A positive loop between relish and cuticle proteins and their roles in regulating AMPs expression during bacterial infection in Eriocheir sinensis

Cuticle proteins (CPs) are the vital components of the cuticle and chitin lining covering the digestive tract of crustaceans. In this study, four new CP genes (designated as EsCP3, EsCP4, EsCP5, and EsCP8) were initially cloned and identified from the Chinese mitten crab Eriocheir sinensis. EsCP3/4/5/8 included 375, 411, 381, and 570 bp open reading frame encoding 124, 136, 126, and 189 amino acid proteins, respectively. Except for EsCP8, EsCP3/4/5 all contained a Chitin_bind_4 domain. EsCP3/4/5/8 were clustered into different groups in the phylogenetic tree. Quantitative real-time PCR results indicated that four EsCP genes have different patterns of tissue distribution. Changes in the expression levels of these four EsCP genes were observed in the intestine of crabs under Vibrio parahaemolyticus challenge. RNA interference assay showed that the knockdown of EsCPs in the intestine could inhibit the expression of antimicrobial peptides (AMPs), including crustins and anti-lipopolysaccharide factors. In addition, the knockdown of EsRelish in the intestine decreased the expression levels of these four EsCP genes. These results indicated that EsCPs were involved in regulating the expression of AMPs, and EsCPs were regulated by EsRelish.

A pH ultra-sensitive hydrated iridium oxyhydroxide films electrochemical sensor for label-free detection of Vibrio parahaemolyticus

Vibrio parahaemolyticus (V. parahaemolyticus) is a major foodborne pathogen, which can cause serious foodborne illnesses like diarrhoea. Rapid on-site detection of foodborne pathogens is an ideal way to respond to foodborne illnesses. Herein, we provide an electrochemical sensor for rapid on-site detection. This sensor utilized a pH-sensitive metal-oxide material for the concurrent isothermal amplification and label-free detection of nucleic acids. Based on a pH-sensitive hydrated iridium oxide oxyhydroxide film (HIROF), the electrode transforms the hydrogen ion compound generated during nucleic acid amplification into potential, so as to achieve a real-time detection. The results can be transmitted to a smartphone via Bluetooth. Moreover, HIROF was applied in nucleic acid device detection, with a super-Nernst sensitivity of 77.6 mV/pH in the pH range of 6.0-8.5, and the sensitivity showed the best results so far. Detection of V. parahaemolyticus by this novel method showed a detection limit of 1.0 × 103 CFU/mL, while the time consumption was only 30 min, outperforming real-time fluorescence loop-mediated isothermal amplification (LAMP). Therefore, the characteristics of compact, portable, and fast make the sensor more widely used in on-site detection.

Characterization of MKK family genes and their responses to temperature stress and Vibrio parahaemolyticus infection in noble scallop Chlamys nobilis

Mitogen-activated protein kinase kinase (MKK), the key element of the Mitogen-activated protein kinase (MAPK) signaling pathway, is crucial for the immune response to adverse environments in aquatic animals. Nevertheless, there is limited information regarding the role of the MKK gene family in mollusks. In our study, genome data and transcriptome were used to identify four MKK genes (CnMKK4, CnMKK5, CnMKK6, and CnMKK7) in the noble scallop. The result of the gene structure, motif analysis, and phylogenetic tree revealed that MKK genes are relatively conserved in bivalves. Moreover, four CnMKK genes were significantly highly expressed in immune-related tissues, suggesting that CnMKKs may related to bivalve immunity. Furthermore, CnMKK6 and CgMKK4 were significantly differentially expressed (P < 0.05) under 24 h of temperature stress, and all CnMKKs were significantly differentially expressed (P < 0.05) under 24 h of Vibrio parahaemolyticus infection. These results showed that the CnMKKs may have a significant impact under biotic and abiotic stresses. In conclusion, the result of the CnMKKs provides valuable insights into comprehending the function of MKK genes in mollusks.

Comparative transcriptomic analysis of hepatopancreas reveals that more genes are involved in the exposure response of Vibrio parahaemolyticus PirAvp compared to PirBvp

Vibrio parahaemolyticus (VP-AHPND) is regarded as one of the main pathogens that caused acute hepatopancreatic necrosis disease (AHPND) in the Pacific white shrimp Litopenaeus vannamei. PirAvp and PirBvp toxin proteins are the main pathogenic proteins of AHPND in shrimp. Knowledge about the mechanism of shrimp response to PirAvp or PirBvp toxin is very helpful for developing new prevention and control strategy of AHPND in shrimp. In this study, the pathological sections showed that after 4 h treatment, significant pathological changes were observed in the PirBvp treated group, and no obvious pathological changes was found in PirAvp treated group. In order to learn the mechanism of shrimp response to PirAvp and PirBvp, comparative transcriptome was applied to analyze the different expressions of genes in the hepatopancreas of shrimp after treatment with PirAvp or PirBvp. A total of 9978 differentially expressed genes (DEGs) were identified between PirAvp or PirBvp-treated and PBS control shrimp, including 6616 DEGs in the PirAvp treated group and 3362 DEGs in the PirBvp treated group. There were 2263 DEGs that were commonly expressed, 4353 DEGs were only expressed in PirAvp VS PBS group and 1099 DEGs were uniquely expressed in PirBvp VS PBS group. Among these DEGs, the anti-apoptosis related pathways and immune response related genes significantly expressed in the commonly expressed DEGs of PirAvp VS PBS group and PirBvp VS PBS group, and small GTPase-mediated signaling and DNA metabolic process might relate to the host special reaction towards PirAvp and PirBvp exposure. The data suggested that the differential expression of these immune and metabolic-related genes in hepatopancreas might contribute to the pathogenicity variations of shrimp to VP-AHPND. The identified genes in this study will be useful for clarifying the response mechanism of shrimp toward different toxins of VP-AHPND and will further provide molecular basis for understanding the pathogenic mechanism of VP-AHPND.

Characterization of a secondary palmitoleoyltransferase of lipid A in Vibrio parahaemolyticus

The detection of pathogenicity and immunogenicity in Vibrio parahaemolyticus poses a significant challenge due to its threat to human health and food safety, which is strongly correlated with lipid A. Lipid A, a critical component found in most Gram-negative bacteria, functions as a hydrophobic anchor for lipopolysaccharide. V. parahaemolyticus synthesizes multiple lipid A species with various secondary acyl chains. In this study, a secondary acyltransferase of lipid A encoded by VP_RS08405 in V. parahaemolyticus was identified. Based on sequence alignment analysis, V. parahaemolyticus VP_RS08405 has high homology to E. coli lpxL, lpxM and lpxP which encode the three secondary acyltransferases of lipid A. Therefore, V. parahaemolyticus VP_RS08405 was cloned into pBAD33, and the resulting pB08405 was introduced in E. coli mutants WHL00 in which lpxL was deleted, WHM00 in which lpxM was deleted, WHP00 in which lpxP was deleted, and WH300 in which lpxL, lpxM and lpxP were deleted. The recombinant strains WHL00/pB08405, WHM00/pB08405, WHP00/pB08405, WH300/pB08405, as well as their vector controls, were grown at normal and low temperatures. Lipid A species were isolated from the above strains and analyzed by using high-performance liquid chromatography-tandem mass spectrometry and thin-layer chromatography. After comparing the secondary acyl alterations of lipid A from different recombinant strains, it is concluded that VP_RS08405 specifically catalyzed the addition of a palmitoleate to the 2'-position of lipid A and its activity is not temperature-sensitive. In addition, to determine the dependence of VP_RS08405 on Kdo, VP_RS08405 was overexpressed in E. coli mutants WH001 in which waaA was deleted, and WH400 in which waaA, lpxL, lpxM and lpxP were deleted. Lipid A species were isolated from WH001/pB08405 and WH400/pB08405, and analyzed. The results show that the function of VP_RS08405 is Kdo-dependent. These findings provide a better understanding of the structural diversity of lipid A in V. parahaemolyticus.

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

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

Differential expression of microRNAs in giant freshwater prawn (Macrobrachium rosenbergii) during the infection of Vibrio parahaemolyticus

MicroRNAs (miRNAs) are a category of small non-coding RNAs regarded as vital regulatory factors in various biological processes, especially immune regulation. The differently expressed miRNAs in Macrobrachium rosenbergii after the challenge of Vibrio parahaemolyticus were identified using high-throughput sequencing. A total of 18 known as well as 12 novel miRNAs were markedly differently expressed during the bacterial infection. The results of the target gene prediction and enrichment analysis indicated that a total of 230 target genes involved in a large variety of signaling pathways and biological processes were mediated by the miRNAs identified in the current research. Additionally, the effects of novel-miR-56, a representative differentially expressed miRNA identified in the previous infection experiment, on the immune-related gene expression in M. rosenbergii were explored. The expression of the immune-related genes including Spätzle1(Spz1), Spz4, Toll-like receptor 1 (TLR1), TLR2, TLR3, immune deficiency (IMD), myeloid differentiation factor 88 (MyD88), anti-lipopolysaccharide factor 1 (ALF1), crustin1, as well as prophenoloxidase (proPO) was significantly repressed in the novel-miR-56-overexpressed prawns. The expression of these genes tested in the novel-miR-56-overexpressed M. rosenbergii was still signally lower than the control in the subsequent V. parahaemolyticus challenge, despite the gene expression in each treatment increased significantly after the infection. Additionally, the cumulative mortality of the agomiR-56-treated prawns was significantly higher than the other treatments post the bacterial challenge. These results suggested that novel-miR-56 might function as a negative regulator of the immune-related gene expression of M. rosenbergii in the innate immune defense against V. parahaemolyticus.

Serodiversity, antibiotic resistance, and virulence genes of Vibrio parahaemolyticus in oysters collected in coastal areas of northwestern Mexico between 2012 and 2020

This study aimed to determine the prevalence of V. parahaemolyticus in oysters from the northwestern coast of Mexico and to identify the serotypes, virulence factors, and antibiotic resistance of the strains. Oyster samples were collected from 2012 to 2020 from the northwest coast of Mexico; biochemical and molecular methods were used to identify V. parahaemolyticus from oysters; antiserum reaction to determine V. parahaemolyticus serotypes, and PCR assays were performed to identify pathogenic (tdh and/or trh) or pandemic (toxRS/new, and/or orf8) strains and antibiotic resistance testing. A total of 441 oyster samples were collected and tested for V. parahaemolyticus. Forty-seven percent of oyster samples were positive for V. parahaemolyticus. Ten different O serogroups and 72 serovars were identified, predominantly serotype O1:KUT with 22.2% and OUT:KUT with 17.3%. Twenty new serotypes that had not been previously reported in our region were identified. We detected 4.3% of pathogenic clones but no pandemic strains. About 73.5% of strains were resistant to at least one antibiotic, mainly ampicillin and ciprofloxacin; 25% were multi-drug resistant. In conclusion, the pathogenic strains in oysters and antibiotic resistance are of public health concern, as the potential for outbreaks throughout northwestern Mexico is well established.

The mannose-binding lectin (MBL) gene cloned from Exopalaemon carinicauda plays a key role in resisting infection by Vibrio parahaemolyticus

Mannose-binding lectin (MBL) is a vital member of the lectin family, crucial for mediating functions within the complement lectin pathway. In this study, following the cloning of the mannose-binding lectin (MBL) gene in the ridgetail white prawn, Exopalaemon carinicauda, we examined its expression patterns across various tissues and its role in combating challenges posed by Vibrio parahaemolyticus. The results revealed that the MBL gene spans 1342 bp, featuring an open reading frame of 972 bp. It encodes a protein comprising 323 amino acids, with a predicted relative molecular weight of 36 kDa and a theoretical isoelectric point of 6.18. The gene exhibited expression across various tissues including the eyestalk, heart, gill, hepatopancreas, stomach, intestine, ventral nerve cord, muscle, and hemolymph, with the highest expression detected in the hepatopancreas. Upon challenge with V. parahaemolyticus, RT-PCR analysis revealed a trend of MBL expression in hepatopancreatic tissues, characterized by an initial increase followed by a subsequent decrease, peaking at 24 h post-infection. Employing RNA interference to disrupt MBL gene expression resulted in a significant increase in mortality rates among individuals challenged with V. parahaemolyticus. Furthermore, we successfully generated the Pet32a-MBL recombinant protein through the construction of a prokaryotic expression vector for conducting in vitro bacterial inhibition assays, which demonstrated the inhibitory effect of the recombinant protein on V. parahaemolyticus, laying a foundation for further exploration into its immune mechanism in response to V. parahaemolyticus challenges.

Transcriptomic and microbiome analyses of copepod Apocyclops royi in response to an AHPND-causing strain of Vibrio parahaemolyticus

Copepods are small crustaceans that live in microorganism-rich aquatic environments and provide a key supply of live food for fish and shellfish larviculture. To better understand the host-pathogen interaction between the copepod and Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (VPAHPND), the comparative transcriptome and microbiome analyses were conducted in copepod Apocyclops royi-TH following VPAHPND infection. Transcriptome analysis identified a total of 836 differentially expressed genes, with 275 upregulated and 561 downregulated genes. Subsequent analysis showed that a total of 37 differentially expressed genes were associated with the innate immune system, including 16 upregulated genes related to Toll-like receptor signaling pathway, antimicrobial peptides, and stress response genes, and 21 downregulated genes associated with immunological modulators, signaling molecules, and apoptosis-related proteins. Analysis of the copepod microbiome following VPAHPND infection showed that the microbes changed significantly after bacterial infection, with a reduced alpha diversity accompanied by the increased level of Proteobacteria and decreased levels of Bdellovibrionota, Bacteroidota, and Verrucomicrobiota. The population of Vibrio genera were increased significantly, while several other genera, including Denitromonas, Nitrosomonas, Blastopirellula, Fusibacter, Alteromonas, KI89A_clade, and Ruegeria, were decreased significantly after infection. These findings suggest that VPAHPND infection has a significant impact on the immune defense and the composition of the copepod microbiota.

Construction and characterization of different hemolysin gene deletion strains in Vibrio parahaemolyticus (ΔhlyA, ΔhlyIII) and evaluation of their virulence

Vibrio parahaemolyticus, a halophilic food-borne pathogen, possesses an arsenal of virulence factors. The pathogenicity of V. parahaemolyticus results from a combination of various virulence factors. HlyA and hlyIII genes are presumed to function in hemolysis, in addition to tdh and trh in V. parahaemolyticus. To confirm the hemolytic function of genes hlyA and hlyIII, ΔhlyA and ΔhlyIII strains of V. parahaemolyticus were separately constructed via homologous recombination. The cytotoxicity and pathogenicity of the ΔhlyA and ΔhlyIII strains were evaluated using a Tetrahymena-Vibrio co-culture model and an immersion challenge in Litopenaeus vannamei. Results indicated that the hemolytic activity of the ΔhlyA and ΔhlyIII strains decreased by approximately 31.4 % and 24.9 % respectively, compared to the WT strain. Both ΔhlyA and ΔhlyIII exhibited reduced cytotoxicity towards Tetrahymena. Then shrimp infection experiments showed LD50 values for ΔhlyA and ΔhlyIII of 3.06 × 108 CFU/mL and 1.23 × 108 CFU/mL, respectively, both higher than the WT strain's value of 2.57 × 107 CFU/mL. Histopathological observations revealed that hepatopancreas from shrimps challenged with ΔhlyA and ΔhlyIII exhibited mild symptoms, whereas those challenged with the WT strain displayed severe AHPND. These findings indicate that the ΔhlyA and ΔhlyIII strains are significantly less virulent than the WT strain. In conclusion, both hlyA and hlyIII are vital virulence genes involved in hemolytic and cytotoxic of V. parahaemolyticus.