Further characterization of Vibrio vulnificus rugose variants and identification of a capsular and rugose exopolysaccharide gene cluster

Comprehensive Genomic and Evolutionary Analysis of Biofilm Matrix Clusters and Proteins in the Vibrio Genus

Vibrio cholerae pathogens cause cholera, an acute diarrheal disease resulting in significant morbidity and mortality worldwide. Biofilms in vibrios enhance their survival in natural ecosystems and facilitate transmission during cholera outbreaks. Critical components of the biofilm matrix include the Vibrio polysaccharides produced by the vps-1 and vps-2 gene clusters and the biofilm matrix proteins encoded in the rbm gene cluster, together comprising the biofilm matrix cluster. However, the biofilm matrix clusters and their evolutionary patterns in other Vibrio species remain underexplored. In this study, we systematically investigated the distribution, diversity, and evolution of biofilm matrix clusters and proteins across the Vibrio genus. Our findings reveal that these gene clusters are sporadically distributed throughout the genus, even appearing in species phylogenetically distant from V. cholerae. Evolutionary analysis of the major biofilm matrix proteins RbmC and Bap1 shows that they are structurally and sequentially related, having undergone structural domain and modular alterations. Additionally, a novel loop-less Bap1 variant was identified, predominantly represented in two phylogenetically distant Vibrio cholerae subspecies clades that share specific gene groups associated with the presence or absence of the protein. Furthermore, our analysis revealed that rbmB, a gene involved in biofilm dispersal, shares a recent common ancestor with Vibriophage tail proteins, suggesting that phages may mimic host functions to evade biofilm-associated defenses. Our study offers a foundational understanding of the diversity and evolution of biofilm matrix clusters in vibrios, laying the groundwork for future biofilm engineering through genetic modification.

Vibrio parahaemolyticus and Vibrio vulnificus in vitro colonization on plastics influenced by temperature and strain variability

Marine bacteria often exist in biofilms as communities attached to surfaces, like plastic. Growing concerns exist regarding marine plastics acting as potential vectors of pathogenic Vibrio, especially in a changing climate. It has been generalized that Vibrio vulnificus and Vibrio parahaemolyticus often attach to plastic surfaces. Different strains of these Vibrios exist having different growth and biofilm-forming properties. This study evaluated how temperature and strain variability affect V. parahaemolyticus and V. vulnificus biofilm formation and characteristics on glass (GL), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS). All strains of both species attached to GL and all plastics at 25, 30, and 35°C. As a species, V. vulnificus produced more biofilm on PS (p ≤ 0.05) compared to GL, and biofilm biomass was enhanced at 25°C compared to 30° (p ≤ 0.01) and 35°C (p ≤ 0.01). However, all individual strains' biofilm biomass and cell densities varied greatly at all temperatures tested. Comparisons of biofilm-forming strains for each species revealed a positive correlation (r = 0.58) between their dry biomass weight and OD₅₇₀ values from crystal violet staining, and total dry biofilm biomass for both species was greater (p ≤ 0.01) on plastics compared to GL. It was also found that extracellular polymeric substance (EPS) chemical characteristics were similar on all plastics of both species, with extracellular proteins mainly contributing to the composition of EPS. All strains were hydrophobic at 25, 30, and 35°C, further illustrating both species' affinity for potential attachment to plastics. Taken together, this study suggests that different strains of V. parahaemolyticus and V. vulnificus can rapidly form biofilms with high cell densities on different plastic types in vitro. However, the biofilm process is highly variable and is species-, strain-specific, and dependent on plastic type, especially under different temperatures.

Biofilm formation of pathogenic bacteria isolated from aquatic animals

Bacterial biofilm formation is one of the dynamic processes, which facilitates bacteria cells to attach to a surface and accumulate as a colony. With the help of biofilm formation, pathogenic bacteria can survive by adapting to their external environment. These bacterial colonies have several resistance properties with a higher survival rate in the environment. Especially, pathogenic bacteria can grow as biofilms and can be protected from antimicrobial compounds and other substances. In aquaculture, biofilm formation by pathogenic bacteria has emerged with an increased infection rate in aquatic animals. Studies show that Vibrio anguillarum, V. parahaemolyticus, V. alginolyticus, V. harveyi, V. campbellii, V. fischeri, Aeromonas hydrophila, A. salmonicida, Yersinia ruckeri, Flavobacterium columnare, F. psychrophilum, Piscirickettsia salmonis, Edwardsiella tarda, E. ictaluri, E. piscicida, Streptococcus parauberis, and S. iniae can survive in the environment by transforming their planktonic form to biofilm form. Therefore, the present review was intended to highlight the principles behind biofilm formation, major biofilm-forming pathogenic bacteria found in aquaculture systems, gene expression of those bacterial biofilms and possible controlling methods. In addition, the possibility of these pathogenic bacteria can be a serious threat to aquaculture systems.

Prevalence, detection of virulence genes and antimicrobial susceptibility of pathogen Vibrio species isolated from different types of seafood samples at "La Nueva Viga" market in Mexico City

Some Vibrio species are important human pathogens owing to they cause infectious diseases such as gastroenteritis, wound infections, septicemia or even death. Many of these illnesses are associated with consumption of contaminated seafood. In the present study, we evaluated the presence of pathogenic Vibrio species, their virulence and antimicrobial susceptibility from 285 different kind of seafood samples from "La Nueva Viga" market in Mexico City. The PCR assay was used for amplification the vppC (collagenase), vmh (hemolysin), tlh (thermolabile hemolysin), and vvhA (hemolytic cytolysin) genes that are specific to Vibrio alginolyticus (detected in 27%), Vibrio mimicus (23.2%), Vibrio parahaemolyticus (28.8%) and Vibrio vulnificus (21.1%), respectively. Several genes encoding virulence factors were amplified. These included V. alginolyticus: pvuA (17.9%), pvsA (50%), wza and lafA (100%); V. mimicus: iut A (60%), toxR (100%); V. parahaemolyticus: pvuA (58.7%), pvsA (26.1%), wza (2.2%), and lafA (100%); and V. vulnificus: wcrA (77.5%), gmhD (57.5%), lafA (100%) and motA (30%). The antibiotic susceptibility of the Vibrio species isolates revealed that most of them were resistant to ampicillin, cephalothin and carbenicillin but susceptible to pefloxacin and trimethoprim-sulfamethoxazole. Our results indicated a high prevalence of pathogenic Vibrio species in seafood, a high presence of virulence genes and that Vibrio species continuously exposed to antibiotics, therefore, consumption of these kind of seafood carries a potential risk for foodborne illness.

Capsular polysaccharide production and serum survival of Vibrio vulnificus are dependent on antitermination control by RfaH

The human pathogen Vibrio vulnificus undergoes phase variation among colonial morphotypes, including a virulent opaque form which produces capsular polysaccharide (CPS) and a translucent phenotype that produces little or no CPS and is attenuated. Here, we found that a V. vulnificus mutant defective for RfaH antitermination control showed a diminished capacity to undergo phase variation and displayed significantly reduced distal gene expression within the Group I CPS operon. Moreover, the rfaH mutant produced negligible CPS and was highly sensitive to killing by normal human serum, results which indicate that RfaH is likely essential for virulence in this bacterium.

A novel phase variant of the cholera pathogen shows stress-adaptive cryptic transcriptomic signatures

Background

In a process known as phase variation, the marine bacterium and cholera pathogen Vibrio cholerae alternately expresses smooth or rugose colonial phenotypes, the latter being associated with advanced biofilm architecture and greater resistance to ecological stress. To define phase variation at the transcriptomic level in pandemic V. cholerae O1 El Tor strain N16961, we compared the RNA-seq-derived transcriptomes among the smooth parent N16961, its rugose derivative (N16961R) and a smooth form obtained directly from the rugose at high frequencies consistent with phase variation (N16961SD).

Results

Differentially regulated genes which clustered into co-expression groups were identified for specific cellular functions, including acetate metabolism, gluconeogenesis, and anaerobic respiration, suggesting an important link between these processes and biofilm formation in this species. Principal component analysis separated the transcriptome of N16961SD from the other phase variants. Although N16961SD was defective in biofilm formation, transcription of its biofilm-related vps and rbm gene clusters was nevertheless elevated as judged by both RNA-seq and RT-qPCR analyses. This transcriptome signature was shared with N16961R, as were others involving two-component signal transduction, chemotaxis, and c-di-GMP synthesis functions.

Conclusions

Precise turnarounds in gene expression did not accompany reversible phase transitions (i.e., smooth to rugose to smooth) in the cholera pathogen. Transcriptomic signatures consisting of up-regulated genes involved in biofilm formation, environmental sensing and persistence, chemotaxis, and signal transduction, which were shared by N16961R and N16961SD variants, may implicate a stress adaptation in the pathogen that facilitates transition of the N16961SD smooth form back to rugosity should environmental conditions dictate.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3233-x) contains supplementary material, which is available to authorized users.

Role of extracellular matrix protein CabA in resistance of Vibrio vulnificus biofilms to decontamination strategies

Biofilms are recalcitrant and raise safety problems in the food industry. In this study, the role of CabA, an extracellular matrix protein, in the resistance of the biofilms of Vibrio vulnificus, a foodborne pathogen, to decontamination strategies was investigated. Biofilms of the cabA mutant revealed reduced resistance to detachment by vibration and disinfection by sodium hypochlorite compared to the biofilms of the parental wild type in vitro. The reduced resistance of the cabA mutant biofilms was complemented by introducing a recombinant cabA, indicating that the reduced resistance of the cabA mutant biofilms is caused by the inactivation of cabA. The expression of cabA was induced in cells bound to oyster, the primary vehicle of the pathogen. The cabA mutant biofilms on oyster are defective in biomass and resistance to detachment and disinfection. The bacterial cells in the wild-type biofilms are clustered by filaments which are not apparent in the cabA mutant biofilms. The combined results indicated that CabA contributes to the structural integrity of V. vulnificus biofilms possibly by forming filaments in the matrix and thus rendering the biofilms robust, suggesting that CabA could be a target to control V. vulnificus biofilms on oyster.

Manganese is an additional cation that enhances colonial phase variation of Vibrio vulnificus

Vibrio vulnificus, an inhabitant of marine and estuarine environments around the world, is the leading cause of reported seafood-related deaths in the United States. Disease is caused by opaque colony-forming strains that produce capsular polysaccharide, loss of which results in an unencapsulated translucent phenotype with diminished virulence potential. Rugose is a third phenotypic variant of V. vulnificus, and produces a separate exopolysaccharide that results in a dry, wrinkled appearance and the ability to form profuse biofilms. Phase variation among these three phenotypes is influenced by several environmental factors, including the presence of calcium in the medium (Garrison-Schilling et al.). In this study, we have identified a second cation, manganese, which substantially increases the propensity of opaque V. vulnificus strains to switch to translucent or rugose phenotypes. In comparative studies, manganese and calcium promoted switching to the same phenotype for some strains but to different phenotypes for others, results of which indicate that the two cations do not always promote the same changes in underlying gene expression. The data here provide further evidence that exposure of V. vulnificus to select cations results in phenotypic changes that impact both virulence capacity and ecology of the organism.

The cabABC Operon Essential for Biofilm and Rugose Colony Development in Vibrio vulnificus

A transcriptome analysis identified Vibrio vulnificus cabABC genes which were preferentially expressed in biofilms. The cabABC genes were transcribed as a single operon. The cabA gene was induced by elevated 3′,5′-cyclic diguanylic acid (c-di-GMP) and encoded a calcium-binding protein CabA. Comparison of the biofilms produced by the cabA mutant and its parent strain JN111 in microtiter plates using crystal-violet staining demonstrated that CabA contributed to biofilm formation in a calcium-dependent manner under elevated c-di-GMP conditions. Genetic and biochemical analyses revealed that CabA was secreted to the cell exterior through functional CabB and CabC, distributed throughout the biofilm matrix, and produced as the biofilm matured. These results, together with the observation that CabA also contributes to the development of rugose colony morphology, indicated that CabA is a matrix-associated protein required for maturation, rather than adhesion involved in the initial attachment, of biofilms. Microscopic comparison of the structure of biofilms produced by JN111 and the cabA mutant demonstrated that CabA is an extracellular matrix component essential for the development of the mature biofilm structures in flow cells and on oyster shells. Exogenously providing purified CabA restored the biofilm- and rugose colony-forming abilities of the cabA mutant when calcium was available. Circular dichroism and size exclusion analyses revealed that calcium binding induces CabA conformational changes which may lead to multimerization. Extracellular complementation experiments revealed that CabA can assemble a functional matrix only when exopolysaccharides coexist. Consequently, the combined results suggested that CabA is a structural protein of the extracellular matrix and multimerizes to a conformation functional in building robust biofilms, which may render V. vulnificus to survive in hostile environments and reach a concentrated infective dose.

Biofilms are specialized and highly differentiated three-dimensional communities of bacteria encased in an extracellular polymeric matrix (EPM), and the bacteria’s mechanisms to form biofilm are closely linked to their virulence. The EPM often consists of polysaccharides, proteins, nucleic acids, and lipids. Compared to extracellular polysaccharides, little is known about the protein components in the biofilm matrix of Vibrio vulnificus, a foodborne pathogen. In this study, we identified and characterized cabABC genes which were preferentially expressed in biofilms. CabA is a calcium-binding protein and is secreted through functional CabB and CabC. Our results indicated that CabA contributes to the development of biofilm and rugose colony morphology under elevated c-di-GMP conditions. CabA is an extracellular matrix protein crucial for the structural integrity of robust biofilm in flow cells and on oyster shells. Calcium binding induces conformational changes and multimerization of CabA that may render the protein functional to build a well-structured matrix. CabA can assemble a functional matrix extracellularly only when exopolysaccharides (EPS) coexist, indicating that both CabA and EPS are required for the scaffold of V. vulnificus biofilm matrix. This is the first report on a non-polysaccharide matrix component that is essential for the development of the V. vulnificus biofilm structure.

Role of anaerobiosis in capsule production and biofilm formation in Vibrio vulnificus

Vibrio vulnificus, a pervasive human pathogen, can cause potentially fatal septicemia after consumption of undercooked seafood. Biotype 1 strains of V. vulnificus are most commonly associated with human infection and are separated into two genotypes, clinical (C) and environmental (E), based on the virulence-correlated gene. For ingestion-based vibriosis to occur, this bacterium must be able to withstand multiple conditions as it traverses the gastrointestinal tract and ultimately gains entry into the bloodstream. One such condition, anoxia, has yet to be extensively researched in V. vulnificus. We investigated the effect of oxygen availability on capsular polysaccharide (CPS) production and biofilm formation in this bacterium, both of which are thought to be important for disease progression. We found that lack of oxygen elicits a reduction in both CPS and biofilm formation in both genotypes. This is further supported by the finding that pilA, pilD, and mshA genes, all of which encode type IV pilin proteins that aid in attachment to surfaces, were downregulated during anaerobiosis. Surprisingly, E-genotypes exhibited distinct differences in gene expression levels of capsule and attachment genes compared to C-genotypes, both aerobically and anaerobically. The importance of understanding these disparities may give insight into the observed differences in environmental occurrence and virulence potential between these two genotypes of V. vulnificus.

Genetic analysis and prevalence studies of the brp exopolysaccharide locus of Vibrio vulnificus

Phase variation in the Gram-negative human pathogen Vibrio vulnificus involves three colonial morphotypes- smooth opaque colonies due to production of capsular polysaccharide (CPS), smooth translucent colonies as the result of little or no CPS expression, and rugose colonies due to production of a separate extracellular polysaccharide (EPS), which greatly enhances biofilm formation. Previously, it was shown that the brp locus, which consists of nine genes arranged as an operon, is up-regulated in rugose strains in a c-di-GMP-dependent manner, and that plasmid insertions into the locus resulted in loss of rugosity and efficient biofilm production. Here, we have used non-polar mutagenesis to assess the involvement of individual brp genes in production of EPS and related phenotypes. Inactivation of genes predicted to be involved in various stages of EPS biosynthesis eliminated both the rugose colonial appearance and production of EPS, while knockout of a predicted flippase function involved in EPS transport resulted in a dry, lightly striated phenotype, which was associated with a reduction of brp-encoded EPS on the cell surface. All brp mutants retained the reduced motility characteristic of rugose strains. Lastly, we provide evidence that the brp locus is highly prevalent among strains of V. vulnificus.

Role of capsular polysaccharide (CPS) in biofilm formation and regulation of CPS production by quorum-sensing in Vibrio vulnificus

Extracellular polysaccharides, such as lipopolysaccharide and loosely associated exopolysaccharides, are essential for Vibrio vulnificus to form biofilms. The role of another major component of the V. vulnificus extracellular matrix, capsular polysaccharide (CPS), which contributes to colony opacity, has been characterized in biofilm formation. A CPS-deficient mutant, whose wbpP gene encoding UDP-GlcNAc C4-epimerase was knocked out, formed significantly more biofilm than wild type, due to increased hydrophobicity of the cell surface, adherence to abiotic surfaces and cell aggregation. To elucidate the direct effect of CPS on biofilm structure, extracted CPS and a CPS-degrading enzyme, α-N-acetylgalactosaminidase, were added in biofilm assays, resulting in reduction and increment of biofilm sizes respectively. Therefore, it is suggested that CPS play a critical role in determining biofilm size by restricting continual growth of mature biofilms. Since CPS is required after maturation, CPS biosynthesis should be controlled in a cell density-dependent manner, e.g. by quorum-sensing (QS) regulation. Analysing transcription of the CPS gene cluster revealed that it was activated by SmcR, a QS master regulator, via binding to the upstream region of the cluster. Therefore, CPS was produced when biofilm cell density reached high enough to turn on QS regulation and limited biofilms to appropriate sizes.

Fitness factors in vibrios: a mini-review

Vibrios are Gram-negative curved bacilli that occur naturally in marine, estuarine, and freshwater systems. Some species include human and animal pathogens, and some vibrios are necessary for natural systems, including the carbon cycle and osmoregulation. Countless in vivo and in vitro studies have examined the interactions between vibrios and their environment, including molecules, cells, whole animals, and abiotic substrates. Many studies have characterized virulence factors, attachment factors, regulatory factors, and antimicrobial resistance factors, and most of these factors impact the organism's fitness regardless of its external environment. This review aims to identify common attributes among factors that increase fitness in various environments, regardless of whether the environment is an oyster, a rabbit, a flask of immortalized mammalian cells, or a planktonic chitin particle. This review aims to summarize findings published thus far to encapsulate some of the basic similarities among the many vibrio fitness factors and how they frame our understanding of vibrio ecology. Factors representing these similarities include hemolysins, capsular polysaccharides, flagella, proteases, attachment factors, type III secretion systems, chitin binding proteins, iron acquisition systems, and colonization factors.

Evidence that thaxtomin C is a pathogenicity determinant of Streptomyces ipomoeae, the causative agent of Streptomyces soil rot disease of sweet potato

Streptomyces ipomoeae is the causal agent of Streptomyces soil rot of sweet potato, a disease marked by highly necrotic destruction of adventitious roots, including the development of necrotic lesions on the fleshy storage roots. Streptomyces potato scab pathogens produce a phytotoxin (thaxtomin A) that appears to facilitate their entrance into host plants. S. ipomoeae produces a less-modified thaxtomin derivative (thaxtomin C) whose role in pathogenicity has not been examined. Here, we cloned and sequenced the thaxtomin gene cluster (txt) of S. ipomoeae, and we then constructed targeted txt mutants that no longer produced thaxtomin C. The mutants were unable to penetrate intact adventitious roots but still caused necrosis on storage-root tissue. These results, taken in context with previous histopathological study of S. ipomoeae infection, suggest that thaxtomin C plays an essential role in inter- and intracellular penetration of adventitious sweet potato roots by S. ipomoeae. Once inside the plant host, the pathogen uses one or more yet-to-be-determined factors to necrotize root tissue, including that of any storage roots it encounters.

Overlapping and unique contributions of two conserved polysaccharide loci in governing distinct survival phenotypes in Vibrio vulnificus

As an aetiological agent of bacterial sepsis and wound infections, Vibrio vulnificus is unique among the Vibrionacea. Its continued environmental persistence and transmission are bolstered by its ability to colonize shellfish and form biofilms on various marine biotic surfaces. We previously identified a polysaccharide locus, brp, which contributes to the survival phenotypes of biofilm formation, rugose colony formation and stress resistance. Here, we describe a second polysaccharide locus, rbd (regulation of biofilm development), which also enhanced biofilm formation when expressed. Despite this functional overlap, the development of stress resistance and rugosity could be uniquely attributed to brp expression, whereas rbd expression augmented aggregate formation. Simultaneous expression of both loci led to the formation of a dramatic pellicle and maximum biofilm formation. Unlike the brp locus, transcription of the rbd locus was regulated not by c-di-GMP, but by a response regulator (RbdG) that was encoded within the locus. We propose that the ability to regulate the expression of polysaccharides with overlapping and unique characteristics in response to different environmental cues enables V. vulnificus to 'fine tune' its biofilm lifestyle to the prevailing environmental conditions and maximally benefit from the characteristics associated with each polysaccharide.

The tra locus of streptomycete plasmid pIJ101 mediates efficient transfer of a circular but not a linear version of the same replicon

Conjugal transfer of circular plasmids in Streptomyces involves a unique mechanism employing few plasmid-encoded loci and the transfer of double-stranded DNA by an as yet uncharacterized intercellular route. Efficient transfer of the circular streptomycete plasmid pIJ101 requires only two plasmid loci: the pIJ101 tra gene, and as a cis-acting function known as clt. Here, we compared the ability of the pIJ101 transfer apparatus to promote conjugal transfer of circular versus linear versions of the same replicon. While the pIJ101 tra locus readily transferred the circular form of the replicon, the linear version was transferred orders of magnitude less efficiently and all plasmids isolated from the transconjugants were circular, regardless of their original configuration in the donor. Additionally, relatively rare circularization of linear plasmids was detectable in the donor cells, which is consistent with the notion that this event was a prerequisite for transfer by TraB(pIJ101). Linear versions of this same replicon did transfer efficiently, in that configuration, from strains containing the conjugative linear plasmid SLP2. Our data indicate that functions necessary and sufficient for transfer of circular DNA were insufficient for transfer of a related linear DNA molecule. The results here suggest that the conjugation mechanisms of linear versus circular DNA in Streptomyces spp. are inherently different and/or that efficient transfer of linear DNA requires additional components.

Identification of a c-di-GMP-regulated polysaccharide locus governing stress resistance and biofilm and rugose colony formation in Vibrio vulnificus

As an etiological agent of bacterial sepsis and wound infections, Vibrio vulnificus is unique among the Vibrionaceae. Its continued environmental persistence and transmission are bolstered by its ability to colonize shellfish, form biofilms on various marine biotic surfaces, and generate a morphologically and physiologically distinct rugose (R) variant that yields profuse biofilms. Here, we identify a c-di-GMP-regulated locus (brp, for biofilm and rugose polysaccharide) and two transcription factors (BrpR and BrpT) that regulate these physiological responses. Disruption of glycosyltransferases within the locus or either regulator abated the inducing effect of c-di-GMP on biofilm formation, rugosity, and stress resistance. The same lesions, or depletion of intracellular c-di-GMP levels, abrogated these phenotypes in the R variant. The parental and brp mutant strains formed only scant monolayers on glass surfaces and oyster shells, and although the R variant formed expansive biofilms, these were of limited depth. Dramatic vertical expansion of the biofilm structure was observed in the parental strain and R variant, but not the brp mutants, when intracellular c-di-GMP levels were elevated. Hence, the brp-encoded polysaccharide is important for surface colonization and stress resistance in V. vulnificus, and its expression may control how the bacteria switch from a planktonic lifestyle to colonizing shellfish to invading human tissue.

Role of NtrC-regulated exopolysaccharides in the biofilm formation and pathogenic interaction of Vibrio vulnificus

Vibrio vulnificus has been shown to require a global transcription factor, NtrC for mature biofilm development via controlling the biosyntheses of lipopolysaccharide and exopolysaccharide (EPS). Biofilm formation and EPS production were dramatically increased in a medium including a tricarboxylic acid cycle-intermediate as a carbon source. These phenotypes required functional NtrC and were abolished by the addition of ammonium chloride. During the initial stage of biofilm formation, both expression of the ntrC gene and the cellular content of NtrC protein increased. Thus, the regulatory roles of NtrC in EPS biosynthesis were studied with three gene clusters for EPS biosyntheses. Transcriptions of the three clusters were positively controlled by NtrC and showed maximal expression at the early stage of biofilm development. Mutants deficient in one of the genes (VV1_2661, VV2_1579 and VV1_2305) in each cluster showed decreased production of EPS, attenuated ability to form biofilm and lowered cytoadherence to human epithelial cells. However, mutations in VV2_1579 and VV1_2305 resulted in lower cytotoxicity to human cells and mortality to mice than the mutation in VV1_2661. These results demonstrate that NtrC-regulated EPS are crucial in biofilm formation of V. vulnificus, and some EPS components play important roles in interacting with hosts.

Vibrio biofilms: so much the same yet so different

Vibrios are natural inhabitants of aquatic environments and form symbiotic or pathogenic relationships with eukaryotic hosts. Recent studies reveal that the ability of vibrios to form biofilms (i.e. matrix-enclosed, surface-associated communities) depends upon specific structural genes (flagella, pili and exopolysaccharide biosynthesis) and regulatory processes (two-component regulators, quorum sensing and c-di-GMP signaling). Here, we compare and contrast mechanisms and regulation of biofilm formation by Vibrio species, with a focus on Vibrio cholerae, Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio fischeri. Although many aspects are the same, others differ dramatically. Crucial questions that remain to be answered regarding the molecular underpinnings of Vibrio biofilm formation are also discussed.

csrA inhibits the formation of biofilms by Vibrio vulnificus

PCR screening of the shellfish-borne pathogen Vibrio vulnificus revealed csrA-negative strains, and these strains formed increased biofilm compared to csrA-positive strains. Complementation in trans with csrA resulted in reduced biofilm formation, similar to that by csrA(+) strains. Our results provide evidence that csrA inhibits biofilm formation in V. vulnificus.

The putative hybrid sensor kinase SypF coordinates biofilm formation in Vibrio fischeri by acting upstream of two response regulators, SypG and VpsR

Colonization of the Hawaiian squid Euprymna scolopes by the marine bacterium Vibrio fischeri requires the symbiosis polysaccharide (syp) gene cluster, which contributes to symbiotic initiation by promoting biofilm formation on the surface of the symbiotic organ. We previously described roles for the syp-encoded response regulator SypG and an unlinked gene encoding the sensor kinase RscS in controlling syp transcription and inducing syp-dependent cell-cell aggregation phenotypes. Here, we report the involvement of an additional syp-encoded regulator, the putative sensor kinase SypF, in promoting biofilm formation. Through the isolation of an increased activity allele, sypF1, we determined that SypF can function to induce syp transcription as well as a variety of biofilm phenotypes, including wrinkled colony formation, adherence to glass, and pellicle formation. SypF1-mediated transcription of the syp cluster was entirely dependent on SypG. However, the biofilm phenotypes were reduced, not eliminated, in the sypG mutant. These phenotypes were also reduced in a mutant deleted for sypE, another syp-encoded response regulator. However, SypF1 still induced phenotypes in a sypG sypE double mutant, suggesting that SypF1 might activate another regulator(s). Our subsequent work revealed that the residual SypF1-induced biofilm formation depended on VpsR, a putative response regulator, and cellulose biosynthesis. These data support a model in which a network of regulators and at least two polysaccharide loci contribute to biofilm formation in V. fischeri.