LuxQ-LuxU-LuxO pathway regulates biofilm formation by Vibrio parahaemolyticus

Functional role of rpoN in regulating the virulence of non-O1/O139 Vibrio cholerae

Non-O1/O139 Vibrio cholerae is widely distributed in brackish and estuarine ecosystems, which can infect many aquatic animals. RpoN, an alternative sigma factor, plays a critical role in regulating cell functions such as motility, quorum sensing, and virulence. However, the function of rpoN in non-O1/O139 V. cholerae has rarely been reported. In the present study, we constructed the deletion mutant ΔrpoN of non-O1/O139 V. cholerae GXFL1-4 using recombination technology and investigated the function of rpoN through transcriptomic and phenotypic analyses. RNA-seq results showed that many major virulence-related genes were down-regulated in the ΔrpoN mutant, including the type VI secretion system (tssJ, tssA, tagO, tssG), type IV pilus assembly proteins (pilM, pilB), biofilm formation genes (vpsC, cheC), and hemolysin-related genes (hlyD, hlyD-PA). Additionally, phenotypic assays showed that the growth and motility of the ΔrpoN had no apparent change. The deletion of rpoN in non-O1/O139 V. cholerae led to decreased biofilm formation and reduced hemolytic activity. Furthermore, artificial infection tests showed that the virulence of the ΔrpoN mutant toward Macrobrachium rosenbergii was decreased. Our study provides essential insights into the regulatory function of rpoN, revealing that rpoN is a key determinant of virulence regulation in non-O1/O139 V. cholerae.

LitR and its quorum-sensing regulators modulate biofilm formation by Vibrio fischeri

Quorum sensing controls numerous processes ranging from the production of virulence factors to biofilm formation. Biofilms, communities of bacteria that are attached to one another and/or a surface, are common in nature, and when they form, they can produce a quorum of bacteria. One model system to study biofilms is the bacterium Vibrio fischeri, which forms a biofilm that promotes the colonization of its symbiotic host. Many factors promote V. fischeri biofilm formation in vitro, including the symbiosis polysaccharide (SYP) and cellulose, but the role of quorum sensing is currently understudied. Recently, a quorum-sensing-dependent transcription factor, LitR, was shown to negatively influence V. fischeri biofilm formation in the context of a biofilm-overproducing strain. To better understand the importance of LitR, we identified conditions in which the impact of LitR on biofilm formation could be observed in an otherwise wild-type strain and then investigated its role and the roles of upstream quorum regulators in biofilm phenotypes. In static conditions, LitR and its upstream quorum regulators, including autoinducer synthases LuxS and AinS, contributed to control over biofilms that were both SYP and cellulose dependent. In shaking liquid conditions, LitR and AinS contributed to control over biofilms that were primarily cellulose dependent. LitR modestly inhibited cellulose transcription in a manner that depended on the transcription factor VpsR. These findings expand our understanding of LitR and the quorum-sensing pathway in the physiology of V. fischeri and illuminate negative control mechanisms that prevent robust biofilm formation by wild-type V. fischeri under laboratory conditions.IMPORTANCEQuorum sensing is a key regulatory mechanism that controls diverse phenotypes in numerous bacteria, including Vibrio fischeri. In many microbes, quorum sensing has been shown to control biofilm formation, yet in V. fischeri, the link between quorum sensing and biofilm formation has been understudied. This study fills that knowledge gap by identifying roles for the quorum sensing-controlled transcription factor, LitR, and its upstream quorum-sensing regulators, including the autoinducer synthases AinS and LuxS, in inhibiting biofilm formation under specific conditions. It also determined that LitR inhibits the transcription of genes required for cellulose biosynthesis. This work thus expands our understanding of the complex control over biofilm regulation.

Global phylogeography and genomic characterization of Vibrio parahaemolyticus infections in Jilin province, China (2016-2022)

Vibrio parahaemolyticus is a critical foodborne pathogen causing gastroenteritis worldwide. The occurrence of transmission and outbreaks attributed to V. parahaemolyticus has exhibited a notable upward trend during the past two decades. However, comprehensive information on this pathogen in inland cities in China remains scarce. This study shed light on the molecular characteristics, genetic associations, and significant transmission risks through foodborne and fecal-oral routes of 115 V. parahaemolyticus strains obtained from nine inland cities in Jilin Province. Strains were divided into 90 sequence types (STs), with 41 STs that were novel. The predominant sequence type was ST3 (14.78 %, 17/115). The strains exhibited the highest resistance rates to cefazolin and ampicillin. A total of ninety-four antibiotic resistance genes (ARGs) categorized groups based on antibiotic class were identified. The tet(34) (112/115, 97.39 %) and blaCARB (114/115, 99.13 %) genes responsible for tetracycline and β-lactams resistance were present in most isolates. Interestingly, V. parahaemolyticus with the tet(34) gene may not be resistant to tetracycline. Strains with strong biofilm formation ability carry more resistance genes. Atypical virulence genes and virulence genome islands (VPaI) were also identified in the isolated strains. All strains encoded type III secretion system 1 (T3SS1), while 114 isolates encoded type VI secretion system 2 (T6SS2). Notably, T6SS1 was present in 59.55 % of food strains, and pathogenicity genomic islands VPaI-1 to VPaI-5 were found in food-associated isolates. Based on the results of the phylogenetic analysis, clinical strains were closely related within a single cluster, which refers to strains that are more similar to each other than to those outside the group based on specific genetic profiles, while the food isolates were highly diverse. Furthermore, some isolates included in our study indicated potential transmission possibly through sharing of some SNPs between food and clinical-positive V. parahaemolyticus strains from different countries. The study elucidates the genetic characteristics, diversity, and virulence potential of V. parahaemolyticus isolates, thereby enhancing the understanding of the potential risks associated with the cross-border transmission of this pathogen.

Ultrasound combined with FeSO4 facilitated the occurrence of ferroptosis in Vibrio parahaemolyticus

Ultrasound (US) as a sustainable non-thermal sterilization technology that is employed either independently alone or in combination with other processing methods to eliminate food-borne pathogens in the food industry. In the present study, the synergistic effects of US combined with FeSO4 against Vibrio parahaemolyticus were investigated. The results demonstrated that the combination of ultrasound and FeSO4 had an excellent bactericidal activity on V. parahaemolyticus. Treatment with US (100 W) and FeSO4 (8 μM) for 15 min could kill more than 99.9 % cells. Furthermore, the observed cell death was identified as classical ferroptosis, characterized by ferroptosis hallmarks including iron-dependent, ROS burst, membrane damage and lipid peroxide accumulation. Addition of ferroptosis inhibitor liproxstatin-1 alleviated the cell death induced by the combination treatment. Transcriptome analysis further revealed that the US-FeSO4 treatment significantly influenced pathways related to fatty acid metabolism, ferroptosis, biofilm formation, RNA degradation, oxidative phosphorylation and other key processes, which likely contributed to the occurrence of ferroptosis. Based on these findings, we speculated that cavitation effect of US promoted the entry of Fe2+, leading to the generation of free radicals primarily responsible for ferroptosis by US-FeSO4. Taken together, this study provides valuable insights into the biological pathway involved in ultrasound sterilization and presents an alternative strategy to eradicate microorganism in food products.

Isolation and characterization of duck sewage source Salmonella phage P6 and antibacterial activity for recombinant endolysin LysP6

Salmonella is a globally prevalent foodborne pathogen, and adverse events caused by S. Enteritidis and S. Typhimurium are extremely common. With the emergence of drug resistance, there is an urgent need for efficient and specific lytic bacteriophages as alternative to antibiotics in clinical practice. In this study, phage P6 was isolated and screened from effluent and fecal samples from duck farm environments to specifically lyse the duck sources S. Typhimurium and S. Enteritidis. Phage P6 belongs to the genus Lederbergvirus, unclassified Lederbergvirus species. The phage P6 genome did not contained non-coding RNA, virulence genes and drug resistance genes, indicating that phage P6 was biologically safe for clinical applications. Phage P6 lysed 77.78% (28/36) of multidrug-resistant Salmonella and reduced biofilms formed by S. Enteritidis CVCC 3377, 4, and 24, and S. Typhimurium 44 by 44% to 75% within 3 h, and decreased Salmonella in duckling feces by up to 1.64 orders of magnitude. Prokaryotic expression of endolysin LysP6 lysed the chloroform-treated bacterial outer membrane from different serotypes of duck-derived Salmonella and E. coli standard strain ATCC 25922. The host range was expanded compared to phage P6, and the growth of Salmonella was effectively inhibited by LysP6 in conjunction with the membrane permeabilizer EDTA within 24 h. Therefore, phage P6 and phage-derived endolysins LysP6 are suitable for application as potent biocontrol agents to improve poultry health and food safety.

Identification of the global regulatory roles of RraA via the integrative transcriptome and proteome in Vibrio alginolyticus

Bacterial ribonuclease E (RNase E) is vital for posttranscriptional regulation by degrading and processing RNA. The RraA protein inhibits RNase E activity through protein-protein interactions, exerting a global regulatory effect on gene expression. However, the specific role of RraA remains unclear. In this study, we investigated rraA expression in Vibrio alginolyticus ZJ-T and identified three promoters responsible for its expression, resulting in transcripts with varying 5'-UTR lengths. During the stationary phase, rraA was significantly posttranscriptionally inhibited. Deletion of rraA had no impact on bacterial growth in rich medium Luria-Bertani broth with salt (LBS) but resulted in decreased biofilm formation and increased resistance to polymyxin B. Transcriptome analysis revealed 350 differentially expressed genes (DEGs) between the wild type and the rraA mutant, while proteome analysis identified 267 differentially expressed proteins (DEPs). Integrative analysis identified 55 genes common to both DEGs and DEPs, suggesting that RraA primarily affects gene expression at the posttranscriptional level. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis demonstrated that RraA facilitates the conversion of fatty acids, propionic acid, and branched-chain amino acids to acetyl-CoA while enhancing amino acid and peptide uptake. Notably, RraA positively regulates the expression of virulence-associated genes, including those involved in biofilm formation and the type VI secretion system. This study expands the understanding of the regulatory network of RraA through transcriptome analysis, emphasizing the importance of proteomic analysis in investigating posttranscriptional regulation.IMPORTANCERraA is an inhibitor protein of ribonuclease E that interacts with and suppresses its endonucleolytic activity, thereby playing a widespread regulatory role in the degradation and maturation of diverse mRNAs and noncoding small RNAs. However, the physiological functions and associated regulon of RraA in Vibrio alginolyticus have not been fully elucidated. Here, we report that RraA impacts virulence-associated physiological processes, namely, antibiotic resistance and biofilm formation, in V. alginolyticus. By conducting an integrative analysis of both the transcriptome and proteome, we revealed the involvement of RraA in carbon metabolism, amino acid catabolism, and transport, as well as in the type VI secretion system. Collectively, these findings elucidate the regulatory influence of RraA on multiple pathways associated with metabolism and pathogenesis in V. alginolyticus.

The role of rcpA gene in regulating biofilm formation and virulence in Vibrio parahaemolyticus

Vibrio parahaemolyticus (V. parahaemolyticus) is a common seafood-borne pathogen that can colonize the intestine of host and cause gastroenteritis. Biofilm formation by V. parahaemolyticus enhances its persistence in various environments, which poses a series of threats to food safety. This work aims to investigate the function of rcpA gene in biofilm formation and virulence of V. parahaemolyticus. Deletion of rcpA significantly reduced motility, biofilm biomass, and extracellular polymeric substances, and inhibited biofilm formation on a variety of food and food contact surfaces. In mice infection model, mice infected with ∆rcpA strain exhibited a decreased rate of pathogen colonization, a lower level of inflammatory cytokines, and less tissue damage when compared to mice infected with wild type strain. RNA-seq analysis revealed that 374 genes were differentially expressed in the rcpA deletion mutant, which include genes related to quorum sensing, flagellar system, ribosome, type VI secretion system, biotin metabolism and transcriptional regulation. In conclusion, rcpA plays a role in determining biofilm formation and virulence of V. parahaemolyticus and further research is necessitated to fully understand its function in V. parahaemolyticus.

Comparative phenotype and transcriptome analysis revealed the role of ferric uptake regulator (Fur) in the virulence of Vibrio harveyi isolated from diseased American eel (Anguilla rostrata)

Vibrio harveyi is commonly found in salt and brackish water and is recognized as a serious bacterial pathogen in aquaculture worldwide. In this study, we cloned the ferric uptake regulator (fur) gene from V. harveyi wild-type strain HA_1, which was isolated from diseased American eels (Anguilla rostrata) and has a length of 450 bp, encoding 149 amino acids. Then, a mutant strain, HA_1-Δfur, was constructed through homologous recombination of a suicide plasmid (pCVD442). The HA_1-Δfur mutant exhibited weaker biofilm formation and swarming motility, and 18-fold decrease (5.5%) in virulence to the American eels; compared to the wild-type strain, the mutant strain showed time and diameter differences in growth and haemolysis, respectively. Additionally, the adhesion ability of the mutant strain was significantly decreased. Moreover, there were 15 different biochemical indicators observed between the two strains. Transcriptome analysis revealed that 875 genes were differentially expressed in the Δfur mutant, with 385 up-regulated and 490 down-regulated DEGs. GO and KEGG enrichment analysis revealed that, compared to the wild-type strain, the type II and type VI secretion systems (T2SS and T6SS), amino acid synthesis and transport and energy metabolism pathways were significantly down-regulated, but the ABC transporters and biosynthesis of siderophore group non-ribosomal peptides pathways were up-regulated in the Δfur strain. The qRT-PCR results further confirmed that DEGs responsible for amino acid transport and energy metabolism were positively regulated, but DEGs involved in iron acquisition were negatively regulated in the Δfur strain. These findings suggest that the virulence of the Δfur strain was significantly decreased, which is closely related to phenotype changing and gene transcript regulation.

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

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

Targeted phytogenic compounds against Vibrio parahaemolyticus biofilms

As one of main culprit of seafood-associated human illness, Vibrio parahaemolyticus can readily accumulate on biotic or abiotic surfaces to form biofilms in the seafood processing environment. Biofilm formation on various surfaces can provide a protective barrier for viable bacterial cells that are resistant to most traditional bacteriostatic measures. This underscores the necessity and urgency of developing effective alternative strategies to control V. parahaemolyticus biofilms. Plants have always provided an extensive and infinite source of biologically active compounds for "green" antibiofilm agents. This review summarizes recent developments in promising multitargeted phytogenic compounds against V. parahaemolyticus biofilms. This review provides valuable insights into potential research targets that can be pursued further to identify potent natural antibiofilm agents in the food industry.

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

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

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

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

Perturbation of Quorum Sensing after the Acquisition of Bacteriophage Resistance Could Contribute to Novel Traits in Vibrio alginolyticus

Bacteria employ a wide range of molecular mechanisms to confer resistance to bacteriophages, and these mechanisms are continuously being discovered and characterized. However, there are instances where certain bacterial species, despite lacking these known mechanisms, can still develop bacteriophage resistance through intricate metabolic adaptation strategies, potentially involving mutations in transcriptional regulators or phage receptors. Vibrio species have been particularly useful for studying the orchestrated metabolic responses of Gram-negative marine bacteria in various challenges. In a previous study, we demonstrated that Vibrio alginolyticus downregulates the expression of specific receptors and transporters in its membrane, which may enable the bacterium to evade infection by lytic bacteriophages. In our current study, our objective was to explore how the development of bacteriophage resistance in Vibrio species disrupts the quorum-sensing cascade, subsequently affecting bacterial physiology and metabolic capacity. Using a real-time quantitative PCR (rt-QPCR) platform, we examined the expression pattern of quorum-sensing genes, auto-inducer biosynthesis genes, and cell density regulatory proteins in phage-resistant strains. Our results revealed that bacteriophage-resistant bacteria downregulate the expression of quorum-sensing regulatory proteins, such as LuxM, LuxN, and LuxP. This downregulation attenuates the normal perception of quorum-sensing peptides and subsequently diminishes the expression of cell density regulatory proteins, including LuxU, aphA, and LuxR. These findings align with the diverse phenotypic traits observed in the phage-resistant strains, such as altered biofilm formation, reduced planktonic growth, and reduced virulence. Moreover, the transcriptional depletion of aphA, the master regulator associated with low cell density, was linked to the downregulation of genes related to virulence. This phenomenon appears to be phage-specific, suggesting a finely tuned metabolic adaptation driven by phage-host interaction. These findings contribute to our understanding of the role of Vibrio species in microbial marine ecology and highlight the complex interplay between phage resistance, quorum sensing, and bacterial physiology.

Quorum sensing signal synthases enhance Vibrio parahaemolyticus swarming motility

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

Comparative genomic analysis reveals the potential transmission of Vibrio parahaemolyticus from freshwater food to humans

Vibrio parahaemolyticus is an increasingly important foodborne pathogen that cause acute gastroenteritis in humans. However, the prevalence and transmission of this pathogen in freshwater food remains unclear. This study aimed to determine the molecular characteristics and genetic relatedness of V. parahaemolyticus isolates obtained from freshwater food, seafood, environmental, and clinical samples. A total of 138 (46.6%) isolates were detected from 296 food and environmental samples, and 68 clinical isolates from patients. Notably, V. parahaemolyticus was more prevalent in freshwater food (56.7%, 85/150) than in seafood (38.8%, 49/137). Virulence phenotype analyses revealed that the high motility of isolates from freshwater food (40.0%) and clinical isolates (42.0%) was higher than that of isolates from seafood (12.2%), whereas the biofilm-forming capacity of freshwater food isolates (9.4%) was lower than that of seafood (22.4%) and clinical isolates (15.9%). Virulence genes analysis showed that 46.4% of the clinical isolates contained the tdh gene encoding thermostable direct hemolysin (TDH) and only two freshwater food isolates contained the trh gene encoding TDH-related hemolysin (TRH). Multilocus sequence typing (MLST) analysis divided the 206 isolates into 105 sequence types (STs), including 56 (53.3%) novel STs. ST2583, ST469, and ST453 have been isolated from freshwater food and clinical samples. Whole-genome sequence (WGS) analyses revealed that the 206 isolates were divided into five clusters. Cluster II contained isolates from freshwater food and clinical samples, whereas the other clusters contained isolates from seafood, freshwater food, and clinical samples. In addition, we observed that ST2516 had the same virulence pattern, with a close phylogenetic relationship to ST3. The increased prevalence and adaption of V. parahaemolyticus in freshwater food is a potential cause of clinical cases closely related to the consumption of V. parahaemolyticus contaminated freshwater food.

Quorum sensing and QsvR tightly control the transcription of vpa0607 encoding an active RNase II-type protein in Vibrio parahaemolyticus

Vibrio parahaemolyticus, a Gram-negative, halophilic bacterium, is a leading cause of acute gastroenteritis in humans. AphA and OpaR are the master quorum sensing (QS) regulators operating at low cell density (LCD) and high cell density (HCD), respectively. QsvR is an AraC-type protein that integrates into the QS system to control gene expression by directly controlling the transcription of aphA and opaR. However, the regulation of QsvR itself remains unclear to date. In this study, we show that vpa0607 and qsvR are transcribed as an operon, vpa0607-qsvR. AphA indirectly activates the transcription of vpa0607 at LCD, whereas OpaR and QsvR directly repress vpa0607 transcription at HCD, leading to the highest expression levels of vpa0607 occurs at LCD. Moreover, VPA0607 acts as an active RNase II-type protein in V. parahaemolyticus and feedback inhibits the expression of QsvR at the post-transcriptional level. Taken together, this work deepens our understanding of the regulation of QsvR and enriches the integration mechanisms of QsvR with the QS system in V. parahaemolyticus.

Transcriptome analysis of the biofilm formation mechanism of Vibrio parahaemolyticus under the sub-inhibitory concentrations of copper and carbenicillin

Biofilm formation of Vibrio parahaemolyticus enhanced its tolerance to the environment, but caused many serious problems to food safety and human health. In this paper, the effects of copper and carbenicillin (CARB) stress on the formation of the biofilms of V. parahaemolyticus organisms were studied, and RNA sequencing technology was used to compare the differences in transcriptome profiles of the biofilm-related genes of V. parahaemolyticus organisms under different sub-inhibitory stresses. The results proved that V. parahaemolyticus had a large growth difference under the two stresses, copper and CARB at 1/2 minimal inhibitory concentration (MIC), and it could form a stable biofilm under both stress conditions. The amount of biofilm formed under CARB stress was significantly higher than that of copper stress (p < 0.05). Based on the analysis of transcriptome sequencing results 323, 1,550, and 1,296 significantly differential expressed genes were identified in the three treatment groups namely 1/2 MIC CARB, Cu²⁺, and Cu²⁺+CARB. Through COG annotation, KEGG metabolic pathway analysis and gene expression analysis related to biofilm formation, the functional pathways of transcriptome changes affecting V. parahaemolyticus were different in the three treatment groups, and the CARB treatment group was significantly different from the other two groups. These differences indicated that the ABC transport system, two-component system and quorum sensing were all involved in the biofilm formation of the V. parahaemolytic by regulating flagellar motility, extracellular polysaccharides and extracellular polymer synthesis. Exploring the effects of different stress conditions on the transcriptome of V. parahaemolyticus could provide a basis for future research on the complex network system that regulates the formation of bacterial biofilms.

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.

Antibacterial Mechanism of Chitosan-Gentamicin and Its Effect on the Intestinal Flora of Litopenaeus vannamei Infected with Vibrio parahaemolyticus

To explore the application of chitosan-gentamicin conjugate (CS-GT) in inhibiting Vibrio parahaemolyticus (V. parahaemolyticus), which is an important pathogen in aquatic animals worldwide, the antimicrobial activity of CS-GT and the effects of a CS-GT dose on the intestine histopathology and intestinal flora of V. parahaemolyticus-infected shrimps were explored. The results showed that CS-GT possessed broad-spectrum antibacterial activity, with minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and half inhibitory concentration (IC50) of 20.00 ± 0.01, 75.00 ± 0.02 and 18.72 ± 3.17 μg/mL for V. parahaemolyticus, respectively. Further scanning electron microscope and cell membrane damage analyses displayed that the electrostatic interaction of CS-GT with cell membrane strengthened after CS grafted GT, resulting in leakage of nucleic acid and electrolytes of V. parahaemolyticus. On the other hand, histopathology investigation indicated that high (100 mg/kg) and medium (50 mg/kg) doses of CS-GT could alleviate the injury of a shrimp's intestine caused by V. parahaemolyticus. Further 16S rRNA gene sequencing analysis found high and medium dose of CS-GT could effectively inhabit V. parahaemolyticus invasion and reduce intestinal dysfunction. In conclusion, CS-GT possesses good antibacterial activity and could protect shrimps from pathogenic bacteria infection.

Contribution of the EnvZ/OmpR two-component system to growth, virulence and stress tolerance of colistin-resistant Aeromonas hydrophila

Aeromonas hydrophila is an important zoonotic pathogen responsible for septicemia, diarrhea and gastroenteritis, and has attracted considerable attention. The EnvZ/OmpR two-component system (TCS) mediates environmental stress responses in gram-negative bacteria. We investigated the role of the TCS in A. hydrophila by comparing the characteristics of the parental (23-C-23), EnvZ/OmpR knockout (23-C-23:ΔEnvZ/OmpR), and complemented strains (23-C-23:CΔEnvZ/OmpR). Under non-stress conditions, the 23-C-23:ΔEnvZ/OmpR strain showed a significant decrease in growth rate compared to that of 23-C-23. Transcriptome and metabonomic analysis indicated that many metabolic pathways were remarkably affected in the ΔEnvZ/OmpR strain, including the TCA cycle and arginine biosynthesis. In addition, the virulence of the ΔEnvZ/OmpR strain was attenuated in a Kunming mouse model. The ΔEnvZ/OmpR strain exhibited notably reduced tolerance to environmental stresses, including high temperature, different pH conditions, oxidative stress, and high osmotic stress. The downregulated expression of genes related to cell metabolism, motility, and virulence in the ΔEnvZ/OmpR mutant strain was further validated by real-time quantitative PCR. Consequently, our data suggest that the EnvZ/OmpR TCS is required for growth, motility, virulence, and stress response in A. hydrophila, which has significant implications in the development of novel antibacterial and vaccine therapies targeting EnvZ/OmpR against A. hydrophila.

Ferrous sulfate efficiently kills Vibrio parahaemolyticus and protects salmon sashimi from its contamination

The primary seafood-borne pathogen Vibrio parahaemolyticus seriously threats the health of consumers preferring raw-fish products, becoming a global concern in food safety. In the present study, we found ferrous sulfate (FeSO₄), a nutritional iron supplement, could efficiently induce the death of V. parahaemolyticus. Further, the bactericidal mechanisms of FeSO₄ were explored. With a fluorescent probe of Fe²⁺, a significant influx of Fe²⁺ was determined in V. parahaemolyticus exposed to FeSO₄, and the addition of an intracellular Fe²⁺ chelator was able to block the cell death. This suggested that cell death in V. parahaemolyticus induced by FeSO₄ was dependent on the influx of Fe²⁺. It was intriguing that we did not observe the eruption of reactive oxygen species (ROS) and lipid hydroperoxides by Fe²⁺, but the application of liproxstatin-1 (a ferroptosis inhibitor) significantly modified the occurrence of cell death in V. parahaemolyticus. These results suggested FeSO₄-induced cell death in V. parahaemolyticus be a ferroptosis differing from that in mammalian cells. Through transcriptome analysis, it was discovered that the exposure of FeSO₄ disturbed considerable amounts of gene expression in V. parahaemolyticus including those involved in protein metabolism, amide biosynthesis, two-component system, amino acid degradation, carbon metabolism, citrate cycle, pyruvate metabolism, oxidative phosphorylation, and so on. These data suggested that FeSO₄ was a pleiotropic antimicrobial agent against V. parahaemolyticus. Notably, FeSO₄ was able to eliminate V. parahaemolyticus in salmon sashimi as well, without affecting the color, texture, shearing force, and sensory characteristics of salmon sashimi. Taken together, our results deciphered a unique ferroptosis in V. parahaemolyticus by FeSO₄, and highlighted its potential in raw-fish products to control V. parahaemolyticus.

Antimicrobial and anti-biofilm activities of chlorogenic acid grafted chitosan against Staphylococcus aureus

In this work, Chitosan-grafted-chlorogenic acid (CS-g-CA) was prepared by the carbodiimide method. The purpose of this study was to investigate the antibacterial and anti-biofilm activity of CS-g-CA against Staphylococcus aureus (S. aureus). The minimum inhibitory concentration (MIC) of CS-g-CA against S. aureus was identified as 0.625 mg/mL. S. aureus treated with 1/2×MIC of CS-g-CA had a longer logarithmic growth phase than that of the CK group, while 1×MIC and 2×MIC inhibited the growth of bacteria. The damaging effect of CS-g-CA on bacterial cells was analyzed by measuring the activity of cellular antioxidant enzymes (Catalase (CAT) and Glutathione peroxidase (GSH-Px)) and intracellular enzymes (alkaline phosphatase (AKPase) and adenosine triphosphatase (ATPase)). The results of DNA gel electrophoresis illustrated that CS-g-CA disrupted the normal metabolism of bacteria. Scanning electron microscopy (SEM) results showed that S. aureus shrank and died under CS-g-CA treatment. 1×MIC of CS-g-CA can significantly inhibit the formation of biofilms, and 1/2×MIC of CS-g-CA control the swimming speed of S. aureus. In addition, 77.53% mature biofilm and 60.62% extracellular polysaccharide (EPS) in the mature biofilm of S. aureus were eradicated by CS-g-CA at 2×MIC. Confocal laser scanning microscopy (CLSM) observation further confirmed these results. Therefore, CS-g-CA was an antimicrobial and antibiofilm agent to control S. aureus, which can effectively controlling the growth of S. aureus in food, thereby preventing the occurrence of food-borne diseases.

Application and challenge of bacteriophage in the food protection

In recent years, foodborne diseases caused by pathogens have been increasing. Therefore, it is essential to control the growth and transmission of pathogens. Bacteriophages (phages) have the potential to play an important role in the biological prevention, control, and treatment of these foodborne diseases due to their favorable advantages. Phages not only effectively inhibit pathogenic bacteria and prolong the shelf life of food, but also possess the advantages of specificity and an absence of chemical residues. Currently, there are many cases of phage applications in agriculture, animal disease prevention and control, food safety, and the treatment of drug-resistant disease. In this review, we summarize the recent research progress on phages against foodborne pathogenic bacteria, including Escherichia coli, Salmonella, Campylobacter, Listeria monocytogenes, Shigella, Vibrio parahaemolyticus, and Staphylococcus aureus. We also discuss the main issues and their corresponding solutions in the application of phages in the food industry. In recent years, although researchers have discovered more phages with potential applications in the food industry, most researchers use these phages based on their host spectrum, and the application environment is mostly in the laboratory. Therefore, the practical application of these phages in different aspects of the food industry may be unsatisfactory and even have some negative effects. Thus, we suggest that before using these phages, it is necessary to identify their specific receptors. Using their specific receptors as the selection basis for their application and combining phages with other phages or phages with traditional antibacterial agents may further improve their safety and application efficiency. Collectively, this review provides a theoretical reference for the basic research and application of phages in the food industry.

Differential binding of LuxR in response to temperature gauges switches virulence gene expression in Vibrio alginolyticus

Vibrio pathogens must cope with temperature changes for proper thermo-adaptation and virulence gene expression. LuxR is a quorum-sensing (QS) master regulator of vibrios, playing roles in response to temperature alteration. However, the molecular mechanisms how LuxR is involved in adapting to different temperatures in bacteria have not been precisely elucidated. In this study, using chromatin immunoprecipitation and nucleotide sequencing (ChIP-seq), we identified 272 and 22 enriched loci harboring LuxR-binding peaks at ambient temperature (30 ˚C) and heat shock (42 ˚C) in the Vibrio alginolyticus genome, respectively. Analysis with the MEME (multiple EM for motif elicitation) algorithm indicated that the binding motifs of LuxR varied from temperatures. Three novel binding regions (the promoter of orf00292, orf00397 and fadD) of LuxR were identified and verified that the rising temperature causes the decreasing binding affinity of LuxR to these promoters. Meanwhile, the expression of orf00292, orf00397 and fadD were regulated by LuxR. Moreover, the weak binding of LuxR to the promoter of extracellular protease (Asp) was attributed to the attenuated Asp expression at thermal stress conditions. Taken together, our study demonstrated distinct binding characteristics of LuxR in response to temperature changes, thus highlighting LuxR as a thermo-sensor to switch and control virulence gene expression in V. alginolyticus.

Microbial silver resistance mechanisms: recent developments

In this mini-review, after a brief introduction into the widespread antimicrobial use of silver ions and nanoparticles against bacteria, fungi and viruses, the toxicity of silver compounds and the molecular mechanisms of microbial silver resistance are discussed, including recent studies on bacteria and fungi. The similarities and differences between silver ions and silver nanoparticles as antimicrobial agents are also mentioned. Regarding bacterial ionic silver resistance, the roles of the sil operon, silver cation efflux proteins, and copper-silver efflux systems are explained. The importance of bacterially produced exopolysaccharides as a physiological (biofilm) defense mechanism against silver nanoparticles is also emphasized. Regarding fungal silver resistance, the roles of metallothioneins, copper-transporting P-type ATPases and cell wall are discussed. Recent evolutionary engineering (adaptive laboratory evolution) studies are also discussed which revealed that silver resistance can evolve rapidly in bacteria and fungi. The cross-resistance observed between silver resistance and resistance to other heavy metals and antibiotics in bacteria and fungi is also explained as a clinically and environmentally important issue. The use of silver against bacterial and fungal biofilm formation is also discussed. Finally, the antiviral effects of silver and the use of silver nanoparticles against SARS-CoV-2 and other viruses are mentioned. To conclude, silver compounds are becoming increasingly important as antimicrobial agents, and their widespread use necessitates detailed understanding of microbial silver response and resistance mechanisms, as well as the ecological effects of silver compounds. Figure created with BioRender.com.

Characterization of ampicillin-resistant genes in Vibrio parahaemolyticus

Vibrio parahaemolyticus is strongly resistant to ampicillin (AMP). In this study, AMP-resistant genes in V. parahaemolyticus ATCC33846 were characterized. Transcriptomic analysis of V. parahaemolyticus exposed to AMP revealed 4608 differentially transcribed genes, including 670 significantly up-regulated genes and 655 significantly down-regulated genes. Based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses, significantly modulated genes in ATCC33846 under AMP stimulation were observed in the following categories: microbial metabolism in diverse environments, metabolic pathways, bacterial secretion system, citrate cycle, biofilm formation, oxidative phosphorylation, ribosome, citrate cycle, pyruvate metabolism, carbon metabolism, nitrogen metabolism, fatty acid metabolism and tryptophan metabolism. The genes VPA0510, VPA0252, VPA0699, VPA0768, VPA0320, VP0636, VPA1096, VPA0947 and VP1775 were significantly up-regulated at the similar level to blaA in V. parahaemolyticus under AMP stimulation, and their overexpression in V. parahaemolyticus could increase its resistance to AMP. These results indicate that AMP has a global influence on V. parahaemolyticus cells. The findings would provide new insights into the resistant mechanism of V. parahaemolyticus to AMP, which would be helpful for developing novel drugs for treating V. parahaemolyticus infection.

Comparative study on inhibitory effects of ferulic acid and p-coumaric acid on Salmonella Enteritidis biofilm formation

Biofilm cells exhibit higher resistance than their planktonic counterparts to commonly used disinfectants in food industry. Phenolic acids are promising substitute offering less selective pressure than traditional antibiotics. This study aims to evaluate the inhibitory effects of ferulic acid (FA) and p-coumaric acid (p-CA) on Salmonella Enteritidis biofilm formation and explore the underlying inhibitory mechanisms. The minimal inhibitory concentration (MIC) of FA and p-CA were 1.0 and 0.5 mg/ml, respectively. The sub-inhibitory concentration (1/8 MIC) significantly decreased biofilm formation without growth inhibitory effects. The biomass and extracellular polymeric substances (EPS) of S. Enteritidis biofilm as well as the bacterial swimming and chemotaxis abilities were significantly decreased when exposed to sub-MIC concentrations of FA and p-CA. These two phenolic acids showed high affinity to proteins involved in flagella motility and repressed the S. Enteritidis biofilm formation-related gene expressions. Furthermore, these two phenolic acids maintained high antibiofilm efficiency in simulated food processing conditions. This study provided valuable information of multiple phenotypic and molecular responses of S. Enteritidis to these two phenolic acids.

Metagenomic analysis of pioneer biofilm-forming marine bacteria with emphasis on Vibrio gigantis adhesion dynamics

Marine biofilms occur frequently and spontaneously in seawater, on almost any submerged solid surface. At the early stages of colonization, it consists of bacteria and evolves into a more complex community. Using 16S rRNA amplicon sequencing and comparative metagenomics, the composition and predicted functional potential of one- to three-day old bacterial communities in surface biofilms were investigated and compared to that of seawater. This confirmed the autochthonous marine bacterium Vibrio gigantis as an early and very abundant biofilm colonizer, also functionally linked to the genes associated with cell motility, surface attachment, and communication via signaling molecules (quorum sensing), all crucial for biofilm formation. The dynamics of adhesion on a solid surface of V. gigantis alone was also monitored in controlled laboratory conditions, using a newly designed and easily implementable protocol. Resulting in a calculated percentage of bacteria-covered surface, a convincing tendency of spontaneous adhering was confirmed. From the multiple results, its quantified and reproducible adhesion dynamics will be used as a basis for future experiments involving surface modifications and coatings, with the goal of preventing adhesion.

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.

Inhibition effect of epigallocatechin gallate on the growth and biofilm formation of Vibrio parahaemolyticus

Vibrio parahaemolyticus (V. parahaemolyticus) is a common marine foodborne pathogen that causes gastroenteritis. With the long-term use of antibiotics, many bacteria become resistant strains, therefore, developing antibiotic-free antimicrobial strategies is urgent. Epigallocatechin gallate (EGCG) as the abundant constituent of polyphenols in tea extract has broad-spectrum antibacterial activity and non-toxicity. Here, we took advantage of EGCG to evaluate its inhibition effect on the growth of V. parahaemolyticus 17802 and the biofilm formation, and explore its antibacterial mechanism. It was found that EGCG showed antibacterial activity to V. parahaemolyticus 17802, and the minimum inhibitory concentration (MIC) is 128 μg mL^-1 , crystal violet staining and confocal laser scanning microscope (CLSM) evidenced EGCG hindered its biofilm formation. Moreover, the swimming motility and extracellular polysaccharides were also notably inhibited. The antibacterial mechanism was further confirmed by several assays, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), live/dead staining assay, together with membrane permeability assay, which all suggested that EGCG caused damage to cell membrane and made it lose integrity, eventually resulting in the death of V. parahaemolyticus 17802. The bactericidal activity of EGCG verified its potential as a promising candidate to combat foodborne pathogen.

Beyond the ABCs—Discovery of Three New Plasmid Types in Rhodobacterales (RepQ, RepY, RepW)

Copiotrophic marine bacteria of the Roseobacter group (Rhodobacterales, Alphaproteobacteria) are characterized by a multipartite genome organization. We sequenced the genomes of Sulfitobacter indolifex DSM 14862^T and four related plasmid-rich isolates in order to investigate the composition, distribution, and evolution of their extrachromosomal replicons (ECRs). A combination of long-read PacBio and short-read Illumina sequencing was required to establish complete closed genomes that comprised up to twelve ECRs. The ECRs were differentiated in stably evolving chromids and genuine plasmids. Among the chromids, a diagnostic RepABC-8 replicon was detected in four Sulfitobacter species that likely reflects an evolutionary innovation that originated in their common ancestor. Classification of the ECRs showed that the most abundant plasmid system is RepABC, followed by RepA, DnaA-like, and RepB. However, the strains also contained three novel plasmid types that were designated RepQ, RepY, and RepW. We confirmed the functionality of their replicases, investigated the genetic inventory of the mostly cryptic plasmids, and retraced their evolutionary origin. Remarkably, the RepY plasmid of S. pontiacus DSM 110277 is the first high copy-number plasmid discovered in Rhodobacterales.

The Antimicrobial Effect of Melissa officinalis L. Essential Oil on Vibrio parahaemolyticus: Insights Based on the Cell Membrane and External Structure

The study was to evaluate the antimicrobial impacts on Melissa officinalis L. essential oil (MOEO) against Vibrio parahaemolyticus. The minimum inhibitory concentration (MIC) of MOEO on Vibrio parahaemolyticus was 1 μL⋅mL^–1. The kill-time curve exhibited that MOEO had good antimicrobial activity. The analysis of cellular ingredients leakage and cell viability illustrated that MOEO has destruction to the morphology of the cell membrane. The damage to the membrane integrity by MOEO has been confirmed by transmission and scanning electron microscopy, obvious morphological and ultrastructural changes were observed in the treated bacterial cells. The MOEO at 0.5 μL⋅mL^–1 can inhibit the biofilm formation, biofilm motility, and extracellular polysaccharide production. Meanwhile, the qPCR results exhibited MOEO inhibited the expression of virulence genes. The findings showed that MOEO exerted its antimicrobial effect mainly by destroying the membrane, which indicated its potential as a natural food preservative.

Evolution of two-component quorum sensing systems

Quorum sensing (QS) is a cell-to-cell communication system that enables bacteria to coordinate their gene expression depending on their population density, via the detection of small molecules called autoinducers. In this way bacteria can act collectively to initiate processes like bioluminescence, virulence and biofilm formation. Autoinducers are detected by receptors, some of which are part of two-component signal transduction systems (TCS), which comprise of a (usually membrane-bound) sensor histidine kinase (HK) and a cognate response regulator (RR). Different QS systems are used by different bacterial taxa, and their relative evolutionary relationships have not been extensively studied. To address this, we used the Kyoto Encyclopedia of Genes and Genomes (KEGG) database to identify all the QS HKs and RRs that are part of TCSs and examined their conservation across microbial taxa. We compared the combinations of the highly conserved domains in the different families of receptors and response regulators using the Simple Modular Architecture Research Tool (SMART) and KEGG databases, and we also carried out phylogenetic analyses for each family, and all families together. The distribution of the different QS systems across taxa, indicates flexibility in HK–RR pairing and highlights the need for further study of the most abundant systems. For both the QS receptors and the response regulators, our results indicate close evolutionary relationships between certain families, highlighting a common evolutionary history which can inform future applications, such as the design of novel inhibitors for pathogenic QS systems.