Genetics of stress adaptation and virulence in toxigenic Vibrio cholerae

How Safe to Eat Are Raw Bivalves? Host Pathogenic and Public Health Concern Microbes within Mussels, Oysters, and Clams in Greek Markets

Raw-bivalves consumption is a wide trend in Mediterranean countries. Despite the unambiguous nutritional value of seafood, raw consumption of bivalves may involve risks that could pose a significant threat to consumers' health. Their filter-feeding behavior is responsible for the potential hosting of a wide variety of microorganisms, either pathogenic for the bivalves or public health threats. Under this prism, the current study was conducted in an effort to evaluate the risk of eating raw bivalves originating from the two biggest seafood markets in Thessaloniki, the largest production area of bivalves in Greece. Both microbiological and molecular methodologies were applied in order to assess the presence of various harmful microbes, including noroviruses, Bonamia, Marteilia, Esherichia coli, Salmonella, and Vibrio. Results indicated the presence of several Vibrio strains in the analyzed samples, of which the halophilic Vibrio harveyi was verified by 16S rRNA sequencing; other than this, no enteropathogenic Vibrio spp. was detected. Furthermore, although Esherichia coli was detected in several samples, it was mostly below the European Union (EU) legislation thresholds. Interestingly, the non-target Photobacterium damselae was also detected, which is associated with both wound infections in human and aquatic animals. Regarding host pathogenic microorganisms, apart from Vibrio harveyi, the protozoan parasite Marteilia refrigens was identified in oysters, highlighting the continuous infection of this bivalve in Greece. In conclusion, bivalves can be generally characterized as a safe-to-eat raw food, hosting more bivalve pathogenic microbes than those of public health concern.

Pharmacophore-Based Screening & Modification of Amiloride Analogs for targeting the NhaP-type Cation-Proton Antiporter in Vibrio cholerae

Structural and mutational analysis of Vc-NhaP2 identified a putative cation binding pocket formed by antiparallel extended regions of two transmembrane segments (TMSs V/XII) along with TMS VI. Molecular Dynamics (MD) simulations suggested that the flexibility of TMS-V/XII is crucial for the intra-molecular conformational events in Vc-NhaP2. In this study, we developed some putative Vc-NhaP2 inhibitors from Amiloride analogs (AAs). Molecular docking of the modified AAs revealed promising binding. The four selected drugs potentially interacted with functionally important amino acid residues located on the cytoplasmic side of TMS VI, the extended chain region of TMS V and TMS XII and the loop region between TMSs VIIII and IX. Molecular dynamics simulations revealed that binding of the selected drugs can potentially destabilize the Vc-NhaP2 and alters the flexibility of the functionally important TMS VI. The work presents the utility of in silico approaches for the rational identification of potential targets and drugs that could target NhaP2 cation proton antiporter to control Vibrio cholerae. The goal is to identify potential drugs that can be validated in future experiments.

Adaptation to pH stress by Vibrio fischeri can affect its symbiosis with the Hawaiian bobtail squid (Euprymna scolopes)

Many microorganisms engaged in host-microbe interactions pendulate between a free-living phase and a host-affiliated stage. How adaptation to stress during the free-living phase affects host-microbe associations is unclear and understudied. To explore this topic, the symbiosis between Hawaiian bobtail squid (Euprymna scolopes) and the luminous bacterium Vibrio fischeri was leveraged for a microbial experimental evolution study. V. fischeri experienced adaptation to extreme pH while apart from the squid host. V. fischeri was serially passaged for 2000 generations to the lower and upper pH growth limits for this microorganism, which were pH 6.0 and 10.0, respectively. V. fischeri was also serially passaged for 2000 generations to vacillating pH 6.0 and 10.0. Evolution to pH stress both facilitated and impaired symbiosis. Microbial evolution to acid stress promoted squid colonization and increased bioluminescence for V. fischeri, while symbiont adaptation to alkaline stress diminished these two traits. Oscillatory selection to acid and alkaline stress also improved symbiosis for V. fischeri, but the facilitating effects were less than that provided by microbial adaptation to acid stress. In summary, microbial adaptation to harsh environments amid the free-living phase may impact the evolution of host-microbe interactions in ways that were not formerly considered.

Studies on diversity of Vibrio sp. and the prevalence of hapA, tcpI, st, rtxA&C, acfB, hlyA, ctxA, ompU and toxR genes in environmental strains of Vibrio cholerae from Port Blair bays of South Andaman, India

Vibrio species are widely distributed in the estuarine and coastal waters that possess the greatest threat to human health worldwide. In this study it is aimed to isolate and observe the abundance of Vibrio sp. and prevalence of biomarker genes and antibiotic resistance profile of V. cholerae isolated from the Port Blair bays of South Andaman. A total of 56 water samples were collected from the seven sampling stations of Port Blair bays in which maximum number of Vibrio sp. population density (1.78 × 10⁴) was recorded in Phoenix Bay. Among the 786 isolates 57.38% of the isolates were confirmed as Vibrio sp., Vibrio cholerae and Vibrio parahaemolyticus. PCR results revealed that the prevalence of biomarker genes was recorded maximum in the isolates from Phoenix Bay and Junglighat Bay samples. Upon further analysis, it was observed that the prevalence of hlyA gene (215 bp), was found to be the most widespread biomarker determinant in 84.17% of isolates. Major virulence determinants; ctxA, ompU and toxR genes were not detected in V. cholerae isolates from Port Blair bays. Maximum antibiotic resistance pattern was observed in Phoenix Bay isolates and maximum number of V. cholerae isolates was resistance to tetracycline (60.76%). Cluster and Principal Component Analysis were employed to understand the diversity and distribution of Vibrio isolates and its biomarker genes. Upon PCA analysis seasonal influence was not much perceived in Vibrio species diversity in Port Blair bays and the lack of significant difference in the detection of species diversity in this study is due to resemblance in geographical conditions and sources of pollution.

Vibrio Pathogens: A Public Health Concern in Rural Water Resources in Sub-Saharan Africa

Members of the Vibrio genus are autochthonous inhabitants of aquatic environments and play vital roles in sustaining the aquatic milieu. The genus comprises about 100 species, which are mostly of marine or freshwater origin, and their classification is frequently updated due to the continuous discovery of novel species. The main route of transmission of Vibrio pathogens to man is through drinking of contaminated water and consumption inadequately cooked aquatic food products. In sub-Saharan Africa and much of the developing world, some rural dwellers use freshwater resources such as rivers for domestic activities, bathing, and cultural and religious purposes. This review describes the impact of inadequately treated sewage effluents on the receiving freshwater resources and the associated risk to the rural dwellers that depends on the water. Vibrio infections remain a threat to public health. In the last decade, Vibrio disease outbreaks have created alertness on the personal, economic, and public health uncertainties associated with the impact of contaminated water in the aquatic environment of sub-Saharan Africa. In this review, we carried out an overview of Vibrio pathogens in rural water resources in Sub-Saharan Africa and the implication of Vibrio pathogens on public health. Continuous monitoring of Vibrio pathogens among environmental freshwater and treated effluents is expected to help reduce the risk associated with the early detection of sources of infection, and also aid our understanding of the natural ecology and evolution of Vibrio pathogens.

Characterization of Vibrio cholerae isolates from 1976 to 2013 in Shandong Province, China

Cholera continues to be a serious public health issue in developing countries. We analyzed the epidemiological data of cholera from 1976 to 2013 in Shandong Province, an eastern coastal area of China. A total of 250 Vibrio cholerae isolates were selected for PCR analysis of virulence genes and pulsed-field gel electrophoresis (PFGE). The analysis of the virulence genes showed that the positive rates for tcpA and tcpI were the highest among strains from the southwest region, which had the highest incidence rate of cholera. Low positive rates for tcpA, tcpI and ctxAB among isolates from after 2000 may be an influencing factor contributing to the contemporary decline in cholera incidence rates. Spatiotemporal serotype shifts (Ogawa, Inaba, Ogawa, Inaba and O139) generally correlated with the variations in the PFGE patterns (PIV, PIIIc, PIa, PIIIb, PIIIa, PIb, and PII). O1 strains from different years or regions also had similar PFGE patterns, while O139 strains exclusively formed one cluster and differed from all other O1 strains. These data indicate that V. cholerae isolates in Shandong Province have continually undergone spatiotemporal changes. The serotype switching between Ogawa and Inaba originated from indigenous strains, while the emergence of serogroup O139 appeared to be unrelated to endemic V. cholerae O1 strains.

Plasmid-encoded MCP is involved in virulence, motility, and biofilm formation of Cronobacter sakazakii ATCC 29544

The aim of this study was to elucidate the function of the plasmid-borne mcp (methyl-accepting chemotaxis protein) gene, which plays pleiotropic roles in Cronobacter sakazakii ATCC 29544. By searching for virulence factors using a random transposon insertion mutant library, we identified and sequenced a new plasmid, pCSA2, in C. sakazakii ATCC 29544. An in silico analysis of pCSA2 revealed that it included six putative open reading frames, and one of them was mcp. The mcp mutant was defective for invasion into and adhesion to epithelial cells, and the virulence of the mcp mutant was attenuated in rat pups. In addition, we demonstrated that putative MCP regulates the motility of C. sakazakii, and the expression of the flagellar genes was enhanced in the absence of a functional mcp gene. Furthermore, a lack of the mcp gene also impaired the ability of C. sakazakii to form a biofilm. Our results demonstrate a regulatory role for MCP in diverse biological processes, including the virulence of C. sakazakii ATCC 29544. To the best of our knowledge, this study is the first to elucidate a potential function of a plasmid-encoded MCP homolog in the C. sakazakii sequence type 8 (ST8) lineage.

Isolation of Vibrio cholera El Tor Inaba From Lemna minor and Eichhornia crassipens Roots in Veracruz, Mexico

Background:

During epidemic periods, the strain Vibrio choleraEl Tor has been isolated from the aquatic macrophyte roots of Eichhornia crassipens and Lemna minor, suggesting that aquatic plants could be environmental reservoirs through either a non-specific association or a commensalism relationship. Therefore, it is important to understand V. cholera reservoirs in order to establish prevention strategies against this pathogen.

Objectives:

Our interest was to determine whether V. cholera could be isolated and typified from L. minor and E. crassipens roots.

Materials and Methods:

From 2004 to 2005, plants were collected from various ecological niches and the roots were used to isolate V. cholera. Standard bacteriological, biochemical and serological tests were used for its typification.

Results:

In five out of the nine ecological niches explored, we collected either L. minor or E. crassipens, as these specimens cohabited only in two niches. V. cholera was isolated from both L. minor and E. crassipens roots. The isolated V. cholera showed the same biochemical characteristics as the pure V. cholera strain which was used as a control. The isolated V. cholera corresponded to V. cholera O1 El Tor Inaba, which is the same serotype related to the last outbreak in Mexico.

Conclusions:

For first time V. cholera El Tor Inaba has been isolated several years after the last emergence of cholera in Mexico. A viable and cultivable V. cholera strain, sourced from freshwater niches in E. crassipens and L. minor roots, suggests the importance of these plants as a permanent aquatic reservoir for these organisms. The monitoring of E. crassipens and L. minor is the responsibility of health institutions in order to evaluate the ongoing risks.

Synergistic effect of various virulence factors leading to high toxicity of environmental V. cholerae non-O1/ non-O139 isolates lacking ctx gene : comparative study with clinical strains

Background

Vibrio cholerae non-O1/ non-O139 serogroups have been reported to cause sporadic diarrhoea in humans. Cholera toxins have been mostly implicated for hypersecretion of ions and water into the small intestine. Though most of the V. cholerae non-O1/ non-O139 strains lack these cholera toxins, several other innate virulence factors contribute towards their pathogenicity. The environmental isolates may thus act as reservoirs for potential spreading of these virulence genes in the natural environment which may cause the emergence of epidemic-causing organisms.

Results

The environmental isolates of vibrios were obtained from water samples, zooplanktons and phytoplanktons, from a village pond in Gandhinagar, Gujarat, India. They were confirmed as Vibrio cholerae non-O1/ non-O139 using standard biochemical and serotyping tests. PCR experiments revealed that the isolates lacked ctxA, ctxB, tcpA, zot and ace genes whereas other pathogenicity genes like toxR, rtxC, hlyA, hapA and prtV were detected in these isolates. Compared with epidemic strain V. cholerae O1 El Tor N16961, culture supernatants from most of these isolates caused higher cytotoxicity to HT29 cells and higher hemolytic, hemagglutinin and protease activities. In rabbit ileal loop assays, the environmental isolates showed only 2-4 folds lesser fluid accumulation in comparison to N16961 and a V. cholerae clinical isolate IDH02365 of 2009. Pulsed Field Gel electrophoresis and Random amplification of Polymorphic DNA indicated that these isolates showed considerable diversity and did not share the same clonal lineage even though they were derived from the same water source. All the isolates showed resistance to one or more antibiotics.

Conclusion

Though these environmental isolates lacked the cholera toxins, they seem to have adopted other survival strategies by optimally utilising a diverse array of several other toxins. The current findings indicate the possibility that these isolates could cause some gastroenteric inflammation when ingested and may serve as progenitors for overt disease-causing organisms.

Sequence polymorphisms of rfbT among the Vibrio cholerae O1 strains in the Ogawa and Inaba serotype shifts

Background

Vibrio cholerae serogroup O1 has two major serotypes, Ogawa and Inaba, which may alternate among cholera epidemics. The rfbT gene is responsible for the conversion between the two serotypes. In this study, we surveyed the sequence variance of rfbT in the Ogawa and Inaba strains in China over a 48-year (1961-2008) period in which serotype shifts occurred among epidemic years.

Results

Various mutation events including single nucleotide, short fragment insertions/deletions and transposases insertions, were found in the rfbT gene of the Inaba strains. Ectopically introducing an intact rfbT could overcome the mutations by converting the Inaba serotype to the Ogawa serotype, suggesting the effects of these mutations on the function of RfbT. Characteristic rfbT mutations were recognized in the Inaba strains among Inaba serotype dominant epidemic years which were separate from the Ogawa dominant epidemics. Three distinguishable mutation sites in rfbT between the classical and the El Tor biotype strains were identified and could serve as biotype-specific biomarkers.

Conclusions

Our results provide a comprehensive picture of the rfbT gene mutations among the V. cholerae O1 strains in different epidemic periods, which could be further used as the tracing markers in clonality analysis and dissemination surveillance of the epidemic strains.

Vibrio cholerae VttR(A) and VttR(B) regulatory influences extend beyond the type 3 secretion system genomic island

A subset of non-O1/non-O139 serogroup strains of Vibrio cholerae cause disease using type 3 secretion system (T3SS)-mediated mechanisms. An ∼50-kb genomic island carries genes encoding the T3SS structural apparatus, effector proteins, and two transmembrane transcriptional regulators, VttR(A) and VttR(B), which are ToxR homologues. Previous experiments demonstrated that VttR(A) and VttR(B) are necessary for colonization in vivo and promote bile-dependent T3SS gene expression in vitro. To better understand the scope of genes that are potential targets of VttR(A) and VttR(B) regulation, we performed deep RNA sequencing using O39 serogroup strain AM-19226 and derivatives carrying deletions in vttR(A) and vttR(B) grown in bile. Comparison of the transcript profiles from ΔvttR(A) and ΔvttR(B) mutant strains to the isogenic parent strain confirmed that VttR(A) and VttR(B) regulate expression of some T3SS island genes and provided additional information about relative expression levels and operon organization. Interestingly, the data also suggested that additional genes, located outside the T3SS island and encoding functions involved in motility, chemotaxis, type 6 secretion, transcriptional regulation, and stress responses, may also by regulated by VttR(A) and VttR(B). We verified transcript levels for selected genes by quantitative reverse transcription (RT)-PCR and then focused additional studies on motility and biofilm formation. The results suggest that VttR(A) and VttR(B) act as part of a complex transcriptional network that coordinates virulence gene expression with multiple cellular phenotypes. VttR(A) and VttR(B) therefore represent horizontally acquired transcriptional regulators with the ability to influence global gene expression in addition to modulating gene expression within the T3SS genomic island.

Disulfide bond formation and ToxR activity in Vibrio cholerae

Virulence factor production in Vibrio cholerae is complex, with ToxRS being an important part of the regulatory cascade. Additionally, ToxR is the transcriptional regulator for the genes encoding the major outer membrane porins OmpU and OmpT. ToxR is a transmembrane protein and contains two cysteine residues in the periplasmic domain. This study addresses the influence of the thiol-disulfide oxidoreductase system DsbAB, ToxR cysteine residues and ToxR/ToxS interaction on ToxR activity. The results show that porin production correlates with ToxR intrachain disulfide bond formation, which depends on DsbAB. In contrast, formation of ToxR intrachain or interchain disulfide bonds is dispensable for virulence factor production and in vivo colonization. This study further reveals that in the absence of ToxS, ToxR interchain disulfide bond formation is facilitated, whereat cysteinyl dependent homo- and oligomerization of ToxR is suppressed if ToxS is coexpressed. In summary, new insights into gene regulation by ToxR are presented, demonstrating a mechanism by which ToxR activity is linked to a DsbAB dependent intrachain disulfide bond formation.

Periplasmic proteins encoded by VCA0261-0260 and VC2216 genes together with copA and cueR products are required for copper tolerance but not for virulence in Vibrio cholerae

The bacterial pathogen Vibrio cholerae requires colonizination of the human small intestine to cause cholera. The anaerobic and slightly acidic conditions predominating there enhance toxicity of low copper concentrations and create a selective environment for bacteria with evolved detoxifying mechanisms. We reported previously that the VCA0260, VCA0261 and VC2216 gene products were synthesized only in V. cholerae grown in microaerobiosis or anaerobiosis. Here we show that ORFs VCA0261 and VCA0260 are actually combined into a single gene encoding a 18.7 kDa protein. Bioinformatic analyses linked this protein and the VC2216 gene product to copper tolerance. Following the approach of predict-mutate and test, we describe for the first time, to our knowledge, the copper tolerance systems operating in V. cholerae. Copper susceptibility analyses of mutants in VCA0261-0260, VC2216 or in the putative copper-tolerance-related VC2215 (copA ATPase) and VC0974 (cueR), under aerobic and anaerobic growth, revealed that CopA represents the main tolerance system under both conditions. The VC2216-encoded periplasmic protein contributes to resistance only under anaerobiosis in a CopA-functional background. The locus tag VCA0261-0260 encodes a copper-inducible, CueR-dependent, periplasmic protein, which mediates tolerance in aerobiosis, but under anaerobiosis its role is only evident in CopA knock-out mutants. None of the genes involved in copper homeostasis were required for V. cholerae virulence or colonization in the mouse model. We conclude that copper tolerance in V. cholerae, which lacks orthologues of the periplasmic copper tolerance proteins CueO, CusCFBA and CueP, involves CopA and CueR proteins along with the periplasmic Cot (VCA0261-0260) and CopG (VC2216) V. cholerae homologues.

Vibrio cholerae requires the type VI secretion system virulence factor VasX to kill Dictyostelium discoideum

The type VI secretion system (T6SS) is recognized as an important virulence mechanism in several Gram-negative pathogens. In Vibrio cholerae, the causative agent of the diarrheal disease cholera, a minimum of three gene clusters--one main cluster and two auxiliary clusters--are required to form a functional T6SS apparatus capable of conferring virulence toward eukaryotic and prokaryotic hosts. Despite an increasing understanding of the components that make up the T6SS apparatus, little is known about the regulation of these genes and the gene products delivered by this nanomachine. VasH is an important regulator of the V. cholerae T6SS. Here, we present evidence that VasH regulates the production of a newly identified protein, VasX, which in turn requires a functional T6SS for secretion. Deletion of vasX does not affect export or enzymatic function of the structural T6SS proteins Hcp and VgrG-1, suggesting that VasX is dispensable for the assembly of the physical translocon complex. VasX localizes to the bacterial membrane and interacts with membrane lipids. We present VasX as a novel virulence factor of the T6SS, as a V. cholerae mutant lacking vasX exhibits a phenotype of attenuated virulence toward Dictyostelium discoideum.

Differential gene expression in bacterial symbionts from loliginid squids demonstrates variation between mutualistic and environmental niches

Luminescent bacteria (gamma-Proteobacteria: Vibrionaceae) are found in complex bilobed light organs of both sepiolid and loliginid squids (Mollusca: Cephalopoda). Despite the existence of multiple strain colonization between Vibrio bacteria and loliginid squids, specificity at the genus level still exists and may influence interactions between symbiotic and free-living stages of the symbiont. The environmentally transmitted behaviour of Vibrio symbionts bestows a certain degree of recognition that exists prior and subsequent to the colonization process. Therefore, we identified bacterial genes required for successful colonization of loliginid light organs by examining transcripts solely expressed in either the light organ or free-living stages. Selective capture of transcribed sequences (SCOTS) was used to differentiate genes expressed by the same bacterium when thriving in two different environments (i.e. loliginid light organs and seawater). Genes specific for squid light organs included vulnibactin synthetase, outer membrane protein W and dihydroxy dehydratase, which have been associated with the maintenance of bacterial host associations in other systems. In contrast, genes that were solely expressed in the free-living condition consisted of transcripts recognized as important factors for bacterial survival in the environment. These transcripts included genes for methyl accepting chemotaxis proteins, arginine decarboxylase and chitinase. These results provide valuable information regarding mechanisms determining specificity, establishment, and maintenance of bacteria-squid associations.

Distribution of genes for virulence and ecological fitness among diverse Vibrio cholerae population in a cholera endemic area: tracking the evolution of pathogenic strains

The pathogenic strains of Vibrio cholerae that cause acute enteric infections in humans are derived from environmental nonpathogenic strains. To track the evolution of pathogenic V. cholerae and identify potential precursors of new pathogenic strains, we analyzed 324 environmental or clinical V. cholerae isolates for the presence of diverse genes involved in virulence or ecological fitness. Of 251 environmental non-O1, non-O139 strains tested, 10 (3.9%) carried the toxin coregulated pilus (TCP) pathogenicity island encoding TCPs, and the CTX prophage encoding cholera toxin, whereas another 10 isolates carried the TCP island alone, and were susceptible to transduction with CTX phage. Most V. cholerae O1 and O139 strains carried these two major virulence determinants, as well as the Vibrio seventh pandemic islands (VSP-1 and VSP-2), whereas 23 (9.1%) non-O1, non-O139 strains carried several VSP island genes, but none carried a complete VSP island. Conversely, 30 (11.9%) non-O1, non-O139 strains carried type III secretion system (TTSS) genes, but none of 63 V. cholerae O1 or O139 strains tested were positive for TTSS. Thus, the distribution of major virulence genes in the non-O1, non-O139 serogroups of V. cholerae is largely different from that of the O1 or O139 serogroups. However, the prevalence of putative accessory virulence genes (mshA, hlyA, and RTX) was similar in all strains, with the mshA being most prevalent (98.8%) followed by RTX genes (96.2%) and hlyA (94.6%), supporting more recent assumptions that these genes imparts increased environmental fitness. Since all pathogenic strains retain these genes, the epidemiological success of the strains presumably depends on their environmental persistence in addition to the ability to produce major virulence factors. Potential precursors of new pathogenic strains would thus require to assemble a combination of genes for both ecological fitness and virulence to attain epidemiological predominance.

Cold shock exoribonuclease R (VacB) is involved in Aeromonas hydrophila pathogenesis

In this study, we cloned and sequenced a virulence-associated gene (vacB) from a clinical isolate SSU of Aeromonas hydrophila. We identified this gene based on our recently annotated genome sequence of the environmental isolate ATCC 7966(T) of A. hydrophila and the vacB gene of Shigella flexneri. The A. hydrophila VacB protein contained 798 amino acid residues, had a molecular mass of 90.5 kDa, and exhibited an exoribonuclease (RNase R) activity. The RNase R of A. hydrophila was a cold-shock protein and was required for bacterial growth at low temperature. The vacB isogenic mutant, which we developed by homologous recombination using marker exchange mutagenesis, was unable to grow at 4 degrees C. In contrast, the wild-type (WT) A. hydrophila exhibited significant growth at this low temperature. Importantly, the vacB mutant was not defective in growth at 37 degrees C. The vacB mutant also exhibited reduced motility, and these growth and motility phenotype defects were restored after complementation of the vacB mutant. The A. hydrophila RNase R-lacking strain was found to be less virulent in a mouse lethality model (70% survival) when given by the intraperitoneal route at as two 50% lethal doses (LD(50)). On the other hand, the WT and complemented strains of A. hydrophila caused 80 to 90% of the mice to succumb to infection at the same LD(50) dose. Overall, this is the first report demonstrating the role of RNase R in modulating the expression of A. hydrophila virulence.

Polyphosphate stores enhance the ability of Vibrio cholerae to overcome environmental stresses in a low-phosphate environment

Vibrio cholerae, the causative agent of Asiatic cholera, has been reported to make large quantities of polyphosphate. Inorganic polyphosphate is a ubiquitous molecule with a variety of functions in prokaryotic and eukaryotic cells. We constructed a V. cholerae mutant with a deletion in the polyphosphate kinase (ppk) gene. The mutant was defective in polyphosphate biosynthesis. Deletion of ppk had no significant effect on production of cholera toxin, hemagglutinin/protease, motility, biofilm formation, and colonization of the suckling mouse intestine. The wild type and mutant had similar growth rates in rich and minimal medium and exhibited similar phosphate uptake and alkaline phosphatase induction. In contrast to ppk mutants from other gram-negative bacteria, the V. cholerae mutant survived prolonged starvation in LB medium and artificial seawater basal salts. The ppk mutant was significantly more sensitive to low pH, high salinity, and oxidative stress when it was cultured in low-phosphate minimal medium. The ppk mutant failed to induce catalase when it was downshifted to phosphorus-limiting conditions. Furthermore, the increased sensitivity of the ppk mutant to environmental stressors in phosphate-limited medium correlated with a diminished capacity to synthesize ATP from intracellular reservoirs. We concluded that polyphosphate protects V. cholerae from environmental stresses under phosphate limitation conditions. It has been proposed that toxigenic V. cholerae can survive in estuaries and brackish waters in which phosphorus and/or nitrogen can be a limiting nutrient. Thus, synthesis of large polyphosphate stores could enhance the ability of V. cholerae to survive in the aquatic environment.

Contribution of hemagglutinin/protease and motility to the pathogenesis of El Tor biotype cholera

Vibrio cholerae is a highly motile organism that secretes a Zn-dependent metalloprotease, hemagglutinin/protease (HapA). HapA has been shown to have mucinase activity and contribute to the reactogenicity of live vaccine candidates, but its role in cholera pathogenesis is not yet clear. The contribution of motility to pathogenesis is not fully understood, since conflicting results have been obtained with different strains, mutants, and animal models. The objective of this work was to determine the contribution of HapA and motility to the pathogenesis of El Tor biotype cholera. To this end we constructed isogenic motility (motY) and mucinase (hapA) single and double mutants of an El Tor biotype V. cholerae strain. Mutants were characterized for the expression of major virulence factors in vitro and in vivo. The motility mutant showed a remarkable increase in cholera toxin (CT), toxin coregulated pilus major subunit (TcpA), and HapA production in vitro. Increased TcpA and CT production could be explained by increased transcription of tcpA, ctxA, and toxT. No effect was detected on the transcription of hapA in the motility mutant. The sodium ionophore monensin diminished production of HapA in the parent but not in the motility mutant. Phenamil, a specific inhibitor of the flagellar motor, diminished CT production in the wild-type and motY strains. The hapA mutant showed increased binding to mucin. In contrast, the motY mutation diminished adherence to biotic and abiotic surfaces including mucin. Lack of HapA did not affect colonization in the suckling mouse model. The motility and mucinase defects did not prevent induction of ctxA and tcpA in the mouse intestine as measured by recombinase-based in vivo expression technology. Analysis of mutants in the rabbit ileal loop model showed that both V. cholerae motility and HapA were necessary for full expression of enterotoxicity.