Functional domains of a zinc metalloprotease from Vibrio vulnificus

Stress Responses in Pathogenic Vibrios and Their Role in Host and Environmental Survival

Vibrio is a genus of bacteria commonly found in estuarine, marine, and freshwater environments. Vibrio species have evolved to occupy diverse niches in the aquatic ecosystem, with some having complex lifestyles. About a dozen of the described Vibrio species have been reported to cause human disease, while many other species cause disease in other organisms. Vibrio cholerae causes epidemic cholera, a severe dehydrating diarrheal disease associated with the consumption of contaminated food or water. The human pathogenic non-cholera Vibrio species, Vibrio parahaemolyticus and Vibrio vulnificus, cause gastroenteritis, septicemia, and other extra-intestinal infections. Infections caused by V. parahaemolyticus and V. vulnificus are normally acquired through exposure to sea water or through consumption of raw or undercooked contaminated seafood. The human pathogenic Vibrios are exposed to numerous different stress-inducing agents and conditions in the aquatic environment and when colonizing a human host. Therefore, they have evolved a variety of mechanisms to survive in the presence of these stressors. Here we discuss what is known about important stress responses in pathogenic Vibrio species and their role in bacterial survival.

The Vibriolysin-Like Protease VnpA and the Collagenase ColA Are Required for Full Virulence of the Bivalve Mollusks Pathogen Vibrio neptunius

Vibrio neptunius is an important pathogen of bivalve mollusks worldwide. Several metalloproteases have been described as virulence factors in species of Vibrio that are pathogenic to bivalves, but little is known about the contribution of these potential virulence factors to Vibrio neptunius pathogenesis. In silico analysis of the genome of V. neptunius strain PP-145.98 led to the identification of two hitherto uncharacterized chromosomal loci encoding a probable vibriolysin-like metalloprotease and a putative collagenase, which were designated VnpA and ColA, respectively. Single defective mutants of each gene were obtained in V. neptunius PP-145.98, and the phospholipase, esterase and collagenase activities were studied and compared with those of the wild-type strain. The results showed that the single inactivation of vnpA resulted in a 3-fold reduction in phospholipase/esterase activity. Inactivation of colA reduced the collagenase activity by 50%. Finally, infection challenges performed in oyster larvae showed that ΔvnpA and ΔcolA—single mutant strains of V. neptunius—are between 2–3-fold less virulent than the wild-type strain. Thus, the present work demonstrates that the production of both VnpA and ColA is required for the full virulence of the bivalve pathogen V. neptunius.

A Novel Thermostable Keratinase from Deinococcus geothermalis with Potential Application in Feather Degradation

Keratinase can specifically attack disulfide bridges in keratin to convert them from complex to simplified forms. Keratinase thermal stability has drawn attention to various biotechnological industries. In this study, a keratinase DgeKer was identified from a slightly thermophilic species, D. geothermalis. The in silico analysis showed that DgeKer is composed of signal peptide, N-terminal propeptide, mature domain, and C-terminal extension. DgeKer and its C-terminal extension-truncated enzyme (DgeKer-C) were cloned and expressed in E. coli. The purified DgeKer and DgeKer-C showed maximum activity at 70 °C and pH 9–The thermal stability assay (60 °C) showed that the half-life value of DgeKer and DgeKer-C were 103.45 min and 169.10 min, respectively. DgeKer and DgeKer-C were stable at the range of pH from 9 to 11 and showed good tolerance to some metal ions, surfactants and organic solvent. Furthermore, DgeKer could degrade feathers at 70 °C for 60 min. However, the medium became turbid with obvious softening of barbules after being treated with DgeKer-C, which might be due to C-terminal extension. In summary, a thermostable keratinase DgeKer with high efficiency degradation of feathers may have great potential in industry.

Spatiotemporal Regulation of Vibrio Exotoxins by HlyU and Other Transcriptional Regulators

After invading a host, bacterial pathogens secrete diverse protein toxins to disrupt host defense systems. To ensure successful infection, however, pathogens must precisely regulate the expression of those exotoxins because uncontrolled toxin production squanders energy. Furthermore, inappropriate toxin secretion can trigger host immune responses that are detrimental to the invading pathogens. Therefore, bacterial pathogens use diverse transcriptional regulators to accurately regulate multiple exotoxin genes based on spatiotemporal conditions. This review covers three major exotoxins in pathogenic Vibrio species and their transcriptional regulation systems. When Vibrio encounters a host, genes encoding cytolysin/hemolysin, multifunctional-autoprocessing repeats-in-toxin (MARTX) toxin, and secreted phospholipases are coordinately regulated by the transcriptional regulator HlyU. At the same time, however, they are distinctly controlled by a variety of other transcriptional regulators. How this coordinated but distinct regulation of exotoxins makes Vibrio species successful pathogens? In addition, anti-virulence strategies that target the coordinating master regulator HlyU and related future research directions are discussed.

Characterization of a New M4 Metalloprotease With Collagen-Swelling Ability From Marine Vibrio pomeroyi Strain 12613

The ocean harbors a variety of bacteria that contain huge protease resources and offer a great potential for industrial and biotechnological applications. Here, we isolated a protease-secreting bacterium Vibrio pomeroyi strain 12613 from Atlantic seawater and purified a protease VP9 from strain 12613. VP9 was identified as a metalloprotease of the M4 family. VP9 could hydrolyze casein and gelatin but not elastin and collagen. With gelatin as the substrate, VP9 showed the highest activity at 40°C and pH 6.0–8.0. It was stable at temperatures of 50°C and less and in the range of pH 5.0–11.0. VP9 also had good tolerance to NaCl, non-ionic detergents, and organic solvent methanol. Unlike other M4 metalloproteases, VP9 has distinct collagen-swelling ability, and its collagen-swelling effect was concentration dependent. The relative expansion volume of collagen increased by approximately eightfold after treatment with 10 μM VP9 at 37°C for 12 h. The collagen-swelling mechanism of VP9 on bovine-insoluble type I collagen was further studied. Atomic force microscopy observation and biochemical analyses showed that VP9 can degrade proteoglycans in collagen fibers, resulting in the release of collagen fibrils from collagen fibers and the swelling of the latter. In addition, VP9 can degrade glycoproteins, a non-collagenous constituent interacting with collagen in the skin. The characteristics of VP9, such as sufficient specificity toward proteoglycans and glycoproteins but no activity toward collagen, suggest its promising potential in the unhairing and fiber-opening processing in leather industry.

Phylogeny and life cycle of the zoonotic pathogen Vibrio vulnificus

Vibrio vulnificus is a zoonotic pathogen able to cause diseases in humans and fish that occasionally result in sepsis and death. Most reviews about this pathogen (including those related to its ecology) are clearly biased towards its role as a human pathogen, emphasizing its relationship with oysters as its main reservoir, the role of the known virulence factors as well as the clinic and the epidemiology of the human disease. This review tries to give to the reader a wider vision of the biology of this pathogen covering aspects related to its phylogeny and evolution and filling the gaps in our understanding of the general strategies that V. vulnificus uses to survive outside and inside its two main hosts, the human and the eel, and how its response to specific environmental parameters determines its survival, its death, or the triggering of an infectious process.

The Effect of the Environmental Temperature on the Adaptation to Host in the Zoonotic Pathogen Vibrio vulnificus

Vibrio vulnificus is a zoonotic pathogen that lives in temperate, tropical and subtropical aquatic ecosystems whose geographical distribution is expanding due to global warming. The species is genetically variable and only the strains that belong to the zoonotic clonal-complex can cause vibriosis in both humans and fish (being its main host the eel). Interestingly, the severity of the vibriosis in the eel and the human depends largely on the water temperature (highly virulent at 28°C, avirulent at 20°C or below) and on the iron content in the blood, respectively. The objective of this work was to unravel the role of temperature in the adaptation to the host through a transcriptomic and phenotypic approach. To this end, we obtained the transcriptome of a zoonotic strain grown in a minimum medium (CM9) at 20, 25, 28, and 37°C, and confirmed the transcriptomic results by RT-qPCR and phenotypic tests. In addition, we compared the temperature stimulon with those previously obtained for iron and serum (from eel and human, respectively). Our results suggest that warm temperatures activate adaptive traits that would prepare the bacteria for host colonization (metabolism, motility, chemotaxis, and the protease activity) and fish septicemia (iron-uptake from transferrin and production of O-antigen of high molecular weight) in a generalized manner, while environmental iron controls the expression of a host-adapted virulent phenotype (toxins and the production of a protective envelope). Finally, our results confirm that beyond the effect of temperature on the V. vulnificus distribution in the environment, it also has an effect on the infectious capability of this pathogen that must be taken into account to predict the real risk of V. vulnificus infection caused by global warming.

A novel alkaline protease from alkaliphilic Idiomarina sp. C9-1 with potential application for eco-friendly enzymatic dehairing in the leather industry

Alkaline proteases have a myriad of potential applications in many industrial processes such as detergent, food and feed production, waste management and the leather industry. In this study, we isolated several alkaline protease producing bacteria from soda lake soil samples. A novel serine alkaline protease (AprA) gene from alkaliphilic Idiomarina sp. C9-1 was cloned and expressed in Escherichia coli. The purified AprA and its pre-peptidase C-terminal (PPC) domain-truncated enzyme (AprA-PPC) showed maximum activity at pH 10.5 and 60 °C, and were active and stable in a wide range of pH and temperature. Ca²⁺ significantly improved the thermostability and increased the optimal temperature to 70 °C. Furthermore, both AprA and AprA-PPC showed good tolerance to surfactants and oxidizing and reducing agents. We found that the PPC domain contributed to AprA activity, thermostability and surfactant tolerance. With casein as substrate, AprA and AprA-PPC showed the highest specific activity of 42567.1 U mg⁻¹ and 99511.9 U mg⁻¹, the K_m values of 3.76 mg ml⁻¹ and 3.98 mg ml⁻¹, and the V_max values of 57538.5 U mg⁻¹ and 108722.1 U mg⁻¹, respectively. Secreted expression of AprA-PPC in Bacillus subtilis after 48 h cultivation resulted in yield of 4935.5 U ml⁻¹ with productivity of 102.8 U ml⁻¹ h⁻¹, which is the highest reported in literature to date. Without adding any lime or sodium sulfide, both of which are harmful pollutants, AprA-PPC was effective in dehairing cattle hide and skins of goat, pig and rabbit in 8–12 h without causing significant damage to hairs and grain surface. Our results suggest that AprA-PPC may have great potentials for ecofriendly dehairing of animal skins in the leather industry.

Functional analysis of N-terminal propeptide in the precursor of Vibrio vulnificus metalloprotease by using cell-free translational system

Vibrio vulnificus is a human pathogen causing fatal septicemia with edematous and hemorrhagic skin damage. Among multiple virulence factors, an extracellular metalloprotease termed as V. vulnificus protease (VVP) is known to play a crucial role in eliciting the skin damage. The mature VVP (413 aa) is composed of two domains, the N-terminal core domain with proteolytic activity and the C-terminal domain mediates efficient attachment to protein substrates. However, VVP is produced as an inactive precursor (609 aa) with a signal peptide (24 aa) and propeptide (172 aa). In order to clarify the function of propeptide, a series of DNA fragments encoding the VVP precursor and its various domains were designed and the proteins were expressed in vitro by using cell-free translational system. The results indicated that the propeptide might function as an intramolecular chaperon to promote the proper folding of both N-terminal and C-terminal domains. The obtained results also suggest that the propeptide, itself was unstable and thus digested easily by the enzymes present in cell lysate used for cell-free system. Additionally, the C-terminal domain in VVP found to inhibit the folding of the N-terminal domain in absence of propeptide.

The Fish Pathogen Vibrio vulnificus Biotype 2: Epidemiology, Phylogeny, and Virulence Factors Involved in Warm-Water Vibriosis

Vibrio vulnificus biotype 2 is the etiological agent of warm-water vibriosis, a disease that affects eels and other teleosts, especially in fish farms. Biotype 2 is polyphyletic and probably emerged from aquatic bacteria by acquisition of a transferable virulence plasmid that encodes resistance to innate immunity of eels and other teleosts. Interestingly, biotype 2 comprises a zoonotic clonal complex designated as serovar E that has extended worldwide. One of the most interesting virulence factors produced by serovar E is RtxA1 3 , a multifunctional protein that acts as a lethal factor for fish, an invasion factor for mice, and a survival factor outside the host. Two practically identical copies of rtxA1 3 are present in all biotype 2 strains regardless of the serovar, one in the virulence plasmid and the other in chromosome II. The plasmid also contains other genes involved in survival and growth in eel blood: vep07 , a gene for an outer membrane (OM) lipoprotein involved in resistance to eel serum and vep20 , a gene for an OM receptor specific for eel-transferrin and, probably, other related fish transferrins. All the three genes are highly conserved within biotype 2, which suggests that they are under a strong selective pressure. Interestingly, the three genes are related with transferable plasmids, which emphasizes the role of horizontal gene transfer in the evolution of V. vulnificus in nutrient-enriched aquatic environments, such as fish farms.

Vibrio vulnificus VvpE inhibits mucin 2 expression by hypermethylation via lipid raft-mediated ROS signaling in intestinal epithelial cells

Mucin is an important physical barrier against enteric pathogens. VvpE is an elastase encoded by Gram-negative bacterium Vibrio vulnificus; however, the functional role of VvpE in intestinal mucin (Muc) production is yet to be elucidated. The recombinant protein (r) VvpE significantly reduced the level of Muc2 in human mucus-secreting HT29-MTX cells. The repression of Muc2 induced by rVvpE was highly susceptible to the knockdown of intelectin-1b (ITLN) and sequestration of cholesterol by methyl-β-cyclodextrin. We found that rVvpE induces the recruitment of NADPH oxidase 2 and neutrophil cytosolic factor 1 into the membrane lipid rafts coupled with ITLN to facilitate the production of reactive oxygen species (ROS). The bacterial signaling of rVvpE through ROS production is uniquely mediated by the phosphorylation of ERK, which was downregulated by the silencing of the PKCδ. Moreover, rVvpE induced region-specific methylation in the Muc2 promoter to promote the transcriptional repression of Muc2. In two mouse models of V. vulnificus infection, the mutation of the vvpE gene from V. vulnificus exhibited an increased survival rate and maintained the level of Muc2 expression in intestine. These results demonstrate that VvpE inhibits Muc2 expression by hypermethylation via lipid raft-mediated ROS signaling in the intestinal epithelial cells.

VvpM, an extracellular metalloprotease of Vibrio vulnificus, induces apoptotic death of human cells

A pathogenic bacterium, Vibrio vulnificus produces various extracellular proteases including the elastolytic metalloprotease, VvpE. In silico analysis of its genome revealed a VvpE-homologous protease, VvpM whose proteolytic activity was abolished by specific inhibitors against metalloproteases. To investigate whether this newly identified protease has pathogenic role in host interaction in addition to proteolytic role, human cell lines were incubated with recombinant VvpM (rVvpM). rVvpM-challenged cells showed typical morphological changes found in cells under apoptosis. Apoptotic cell death was further evidenced by estimating the Annexin V-stained cells, whose proportions were dependent upon the concentrations of rVvpM treated to human cells. To elucidate the signaling pathway for VvpM-induced apoptosis, three MAPKs were tested if their activation were mediated by rVvpM. ERK1/2 was phosphorylated by treatment of rVvpM and rVvpM-induced cell death was blocked by a specific inhibitor against ERK1/2. In rVvpM-treated cells, the cytosolic levels of cytochrome c were increased in a VvpM concentration-dependent manner, while the levels of cytochrome c in mitochondria were decreased. Cell deaths were accompanied by apparent cleavages of procaspases-9 and -3 to the active caspases-9 and -3, respectively. Therefore, this study demonstrates that an extracellular metalloprotease of V. vulnificus, VvpM induces apoptosis of human cells via a pathway consisting of ERK activation, cytochrome c release, and then activation of caspases-9 and -3.

Biofilm-degrading enzymes from Lysobacter gummosus

Biofilm-degrading enzymes could be used for the gentle cleaning of industrial and medical devices and the manufacture of biofilm-resistant materials. We therefore investigated 20 species and strains of the bacterial genus Lysobacter for their ability to degrade experimental biofilms formed by Staphylococcus epidermidis, a common nosocomial pathogen typically associated with device-related infections. The highest biofilm-degradation activity was achieved by L. gummosus. The corresponding enzymes were identified by sequencing the L. gummosus genome. Partial purification of the biofilm-degrading activity from an extract of extracellular material followed by peptide mass fingerprinting resulted in the identification of two peptidases (α-lytic protease and β-lytic metalloendopeptidase) that were predicted to degrade bacterial cell walls. In addition, we identified two isoforms of a lysyl endopeptidase and an enzyme similar to metalloproteases from Vibrio spp. Potential peptidoglycan-binding C-terminal fragments of two OmpA-like proteins also co-purified with the biofilm-degrading activity. The L. gummosus genome was found to encode five isoenzymes of α-lytic protease and three isoenzymes of lysyl endopeptidase. These results indicated that the extracellular digestion of biofilms by L. gummosus depends on multiple bacteriolytic and proteolytic enzymes, which could now be exploited for biofilm control.

Extracellular proteolytic enzymes produced by human pathogenic vibrio species

Bacteria in the genus Vibrio produce extracellular proteolytic enzymes to obtain nutrients via digestion of various protein substrates. However, the enzymes secreted by human pathogenic species have been documented to modulate the bacterial virulence. Several species including Vibrio cholerae and V. vulnificus are known to produce thermolysin-like metalloproteases termed vibriolysin. The vibriolysin from V. vulnificus, a causative agent of serious systemic infection, is a major toxic factor eliciting the secondary skin damage characterized by formation of the hemorrhagic brae. The vibriolysin from intestinal pathogens may play indirect roles in pathogenicity because it can activate protein toxins and hemagglutinin by the limited proteolysis and can affect the bacterial attachment to or detachment from the intestinal surface by degradation of the mucus layer. Two species causing wound infections, V. alginolyticus and V. parahaemolyticus, produce another metalloproteases so-called collagenases. Although the detailed pathological roles have not been studied, the collagenase is potent to accelerate the bacterial dissemination through digestion of the protein components of the extracellular matrix. Some species produce cymotrypsin-like serine proteases, which may also affect the bacterial virulence potential. The intestinal pathogens produce sufficient amounts of the metalloprotease at the small intestinal temperature; however, the metalloprotease production by extra-intestinal pathogens is much higher around the body surface temperature. On the other hand, the serine protease is expressed only in the absence of the metalloprotease.

Structural and functional characterization of mature forms of metalloprotease E495 from Arctic sea-ice bacterium Pseudoalteromonas sp. SM495

E495 is the most abundant protease secreted by the Arctic sea-ice bacterium Pseudoalteromonas sp. SM495. As a thermolysin family metalloprotease, E495 was found to have multiple active forms in the culture of strain SM495. E495-M (containing only the catalytic domain) and E495-M-C1 (containing the catalytic domain and one PPC domain) were two stable mature forms, and E495-M-C1-C2 (containing the catalytic domain and two PPC domains) might be an intermediate. Compared to E495-M, E495-M-C1 had similar affinity and catalytic efficiency to oligopeptides, but higher affinity and catalytic efficiency to proteins. The PPC domains from E495 were expressed as GST-fused proteins. Both of the recombinant PPC domains were shown to have binding ability to proteins C-phycocyanin and casein, and domain PPC1 had higher affinity to C-phycocyanin than domain PPC2. These results indicated that the domain PPC1 in E495-M-C1 could be helpful in binding protein substrate, and therefore, improving the catalytic efficiency. Site-directed mutagenesis on the PPC domains showed that the conserved polar and aromatic residues, D26, D28, Y30, Y/W65, in the PPC domains played key roles in protein binding. Our study may shed light on the mechanism of organic nitrogen degradation in the Arctic sea ice.

The Myxococcus xanthus spore cuticula protein C is a fragment of FibA, an extracellular metalloprotease produced exclusively in aggregated cells

Myxococcus xanthus is a soil bacterium with a complex life cycle involving distinct cell fates, including production of environmentally resistant spores to withstand periods of nutrient limitation. Spores are surrounded by an apparently self-assembling cuticula containing at least Proteins S and C; the gene encoding Protein C is unknown. During analyses of cell heterogeneity in M. xanthus, we observed that Protein C accumulated exclusively in cells found in aggregates. Using mass spectrometry analysis of Protein C either isolated from spore cuticula or immunoprecipitated from aggregated cells, we demonstrate that Protein C is actually a proteolytic fragment of the previously identified but functionally elusive zinc metalloprotease, FibA. Subpopulation specific FibA accumulation is not due to transcriptional regulation suggesting post-transcriptional regulation mechanisms mediate its heterogeneous accumulation patterns.

Proteases produced by vibrios

Bacteria of the genus Vibrio are normal habitants of the aquatic environment but the some species are believed to be human pathogens. Pathogenic vibrios produce various pathogenic factors, and the proteases are also recognized to play pathogenic roles in the infection: the direct roles by digesting many kinds of host proteins or indirect roles by processing other pathogenic protein factors. Especially VVP from Vibrio vulnificus is thought to be a major pathogenic factor of the vibrio. Although HA/P, the V. cholerae hemagglutinin/protease, is not a direct toxic factor of cholera vibrio, its significance is an undeniable fact. Production of HA/P is regulated together with major pathogenic factors such as CT (cholera toxin) or TCP (toxin co-regulated pilus) by a quorum-sensing system. HA/P is necessary for full expression of pathogenicity of the vibrio by supporting growth and translocation in the digestive tract. Processing of protein toxins such as CT or El Tor hemolysin is also an important pathogenic role.

Genomic and proteomic analyses of the coral pathogen Vibrio coralliilyticus reveal a diverse virulence repertoire

Vibrio coralliilyticus has been implicated as an important pathogen of coral species worldwide. In this study, the nearly complete genome of Vibrio coralliilyticus strain P1 (LMG23696) was sequenced and proteases implicated in virulence of the strain were specifically investigated. The genome sequence of P1 (5,513,256 bp in size) consisted of 5222 coding sequences and 58 RNA genes (53 tRNAs and at least 5 rRNAs). Seventeen metalloprotease and effector (vgrG, hlyA and hcp) genes were identified in the genome and expressed proteases were also detected in the secretome of P1. As the VcpA zinc-metalloprotease has been considered an important virulence factor of V. coralliilyticus, a vcpA deletion mutant was constructed to evaluate the effect of this gene in animal pathogenesis. Both wild-type and mutant (ΔvcpA) strains exhibited similar virulence characteristics that resulted in high mortality in Artemia and Drosophila pathogenicity bioassays and strong photosystem II inactivation of the coral dinoflagellate endosymbiont (Symbiodinium). In contrast, the ΔvcpA mutant demonstrated higher hemolytic activity and secreted 18 proteins not secreted by the wild type. These proteins included four types of metalloproteases, a chitinase, a hemolysin-related protein RbmC, the Hcp protein and 12 hypothetical proteins. Overall, the results of this study indicate that V. coralliilyticus strain P1 has a diverse virulence repertoire that possibly enables this bacterium to be an efficient animal pathogen.

Assimilation of metal ions bound to porphyrins or porphyrin-peptides by vibrio vulnificus, a human pathogen inhabiting estuarine and marine environments

Vibrio vulnificus, a ubiquitous microorganism in aquatic environments, causes serious septicemia to the immunocompromised host. In addition to protoheme, this species can utilize Fe-TCPP [ferric tetrakis (4-carboxyphenyl) porphine] as an iron source. In the present study, heme c bound covalently to the protein in cytochrome c, as well as the Fe-TCPP complex formed with a nanopeptide with a high affinity, was found to be useful iron sources for V. vulnificus. This bacterium was also revealed to use Zn-TCPP as a single zinc source. However, other metalloporphyrins such as Mn-TCPP and Pt-TCPP delayed the bacterial growth in the broth containing Fe-TCPP, suggesting interference in the iron assimilation. These results indicate that V. vulnificus may acquire metal ions from both free and peptide-bound metalloporphyrins.

TetR-type transcriptional regulator VtpR functions as a global regulator in Vibrio tubiashii

Vibrio tubiashii, a causative agent of severe shellfish larval disease, produces multiple extracellular proteins, including a metalloprotease (VtpA), as potential virulence factors. We previously reported that VtpA is toxic for Pacific oyster (Crassostrea gigas) larvae. In this study, we show that extracellular protease production by V. tubiashii was much reduced by elevated salt concentrations, as well as by elevated temperatures. In addition, V. tubiashii produced dramatically less protease in minimal salts medium supplemented with glucose or sucrose as the sole carbon source than with succinate. We identified a protein that belongs to the TetR family of transcriptional regulators, VtpR, which showed high homology with V. cholerae HapR. We conclude that VtpR activates VtpA production based on the following: (i) a VtpR-deficient V. tubiashii mutant did not produce extracellular proteases, (ii) the mutant showed reduced expression of a vtpA-lacZ fusion, and (iii) VtpR activated vtpA-lacZ in a V. cholerae heterologous background. Moreover, we show that VtpR activated the expression of an additional metalloprotease gene (vtpB). The deduced VtpB sequence showed high homology with a metalloprotease, VhpA, from V. harveyi. Furthermore, the vtpR mutant strain produced reduced levels of extracellular hemolysin, which is attributed to the lower expression of the V. tubiashii hemolysin genes (vthAB). The VtpR-deficient mutant also had negative effects on bacterial motility and did not demonstrate toxicity to oyster larvae. Together, these findings establish that the V. tubiashii VtpR protein functions as a global regulator controlling an array of potential virulence factors.

Molecular analysis of the gene encoding a cold-adapted halophilic subtilase from deep-sea psychrotolerant bacterium Pseudoalteromonas sp. SM9913: cloning, expression, characterization and function analysis of the C-terminal PPC domains

Only a few cold-adapted halophilic proteases have been reported. Here, the gene mcp03 encoding a cold-adapted halophilic protease MCP-03 was cloned from deep-sea psychrotolerant bacterium Pseudoalteromonas sp. SM9913, which contains a 2,130-bp ORF encoding a novel subtilase precursor. The recombinant MCP-03, expressed in Escherichia coli BL21 and purified from fermented broth, is a multi-domain protein with a catalytic domain and two PPC domains. Compared to mesophilic subtilisin Carlsberg, MCP-03 had characteristics of a typical cold-adapted enzyme (e.g., higher activity at low temperatures, lower optimum temperature and higher thermolability). MCP-03 also exhibited good halophilic ability with maximal activity at 3 M NaCl/KCl and good stability in 3 M NaCl. Deletion mutagenesis showed that the C-terminal PPC domains were unnecessary for enzyme secretion but had an inhibitory effect on MCP-03 catalytic efficiency and were essential for keeping MCP-03 thermostable.

Vibrio zinc-metalloprotease causes photoinactivation of coral endosymbionts and coral tissue lesions

BACKGROUND

Coral diseases are emerging as a serious threat to coral reefs worldwide. Of nine coral infectious diseases, whose pathogens have been characterized, six are caused by agents from the family Vibrionacae, raising questions as to their origin and role in coral disease aetiology.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report on a Vibrio zinc-metalloprotease causing rapid photoinactivation of susceptible Symbiodinium endosymbionts followed by lesions in coral tissue. Symbiodinium photosystem II inactivation was diagnosed by an imaging pulse amplitude modulation fluorometer in two bioassays, performed by exposing Symbiodinium cells and coral juveniles to non-inhibited and EDTA-inhibited supernatants derived from coral white syndrome pathogens.

CONCLUSION/SIGNIFICANCE

These findings demonstrate a common virulence factor from four phylogenetically related coral pathogens, suggesting that zinc-metalloproteases may play an important role in Vibrio pathogenicity in scleractinian corals.

Two forms of Vibrio vulnificus metalloprotease VvpE are secreted via the type II general secretion system

Vibrio vulnificus has been known to secrete one form of metalloprotease VvpE (45 kDa) that is cleaved to 34 kDa-VvpE and 11 kDa-C-terminal propeptide via extracellular autoproteolysis. However, we found that extracellular secretion of both the 34 and 45 kDa forms of VvpE began in the early growth phase; moreover, 34 kDa-VvpE existed as the major form in V. vulnificus cell lysates and culture supernatants. In addition, extracellular secretion of both 34 and 45 kDa-VvpE was blocked by mutation of the pilD gene, which encodes for the type IV leader peptidase/N-methyltransferase of the type II general secretion system, and the blocked VvpE secretion was recovered by in trans-complementation of the wild-type pilD gene. These results indicate that 34 kDa-VvpE is the major form secreted along with 45 kDa-VvpE from the early growth phase via the PilD-mediated type II general secretion system.

The extracellular metalloprotease of Vibrio tubiashii is a major virulence factor for pacific oyster (Crassostrea gigas) larvae

Vibrio tubiashii is a recently reemerging pathogen of larval bivalve mollusks, causing both toxigenic and invasive disease. Marine Vibrio spp. produce an array of extracellular products as potential pathogenicity factors. Culture supernatants of V. tubiashii have been shown to be toxic to oyster larvae and were reported to contain a metalloprotease and a cytolysin/hemolysin. However, the structural genes responsible for these proteins have yet to be identified, and it is uncertain which extracellular products play a role in pathogenicity. We investigated the effects of the metalloprotease and hemolysin secreted by V. tubiashii on its ability to kill Pacific oyster (Crassostrea gigas) larvae. While V. tubiashii supernatants treated with metalloprotease inhibitors severely reduced the toxicity to oyster larvae, inhibition of the hemolytic activity did not affect larval toxicity. We identified structural genes of V. tubiashii encoding a metalloprotease (vtpA) and a hemolysin (vthA). Sequence analyses revealed that VtpA shared high homology with metalloproteases from a variety of Vibrio species, while VthA showed high homology only to the cytolysin/hemolysin of Vibrio vulnificus. Compared to the wild-type strain, a VtpA mutant of V. tubiashii not only produced reduced amounts of protease but also showed decreased toxicity to C. gigas larvae. Vibrio cholerae strains carrying the vtpA or vthA gene successfully secreted the heterologous protein. Culture supernatants of V. cholerae carrying vtpA but not vthA were highly toxic to Pacific oyster larvae. Together, these results suggest that the V. tubiashii extracellular metalloprotease is important in its pathogenicity to C. gigas larvae.

Regulation of bacterial protease activity

Proteases, also referred to as peptidases, are the enzymes that catalyse the hydrolysis of peptide bonds in polipeptides. A variety of biological functions and processes depend on their activity. Regardless of the organism's complexity, peptidases are essential at every stage of life of every individual cell, since all protein molecules produced must be proteolytically processed and eventually recycled. Protease inhibitors play a crucial role in the required strict and multilevel control of the activity of proteases involved in processes conditioning both the physiological and pathophysiological functioning of an organism, as well as in host-pathogen interactions. This review describes the regulation of activity of bacterial proteases produced by dangerous human pathogens, focusing on the Staphylococcus genus.

Role of the metalloprotease Vvp and the virulence plasmid pR99 of Vibrio vulnificus serovar E in surface colonization and fish virulence

The virulence for eels of Vibrio vulnificus biotype 2 serovar E (VSE) is conferred by a plasmid that codifies ability to survive in eel serum and cause septicaemia. To find out whether the plasmid and the selected chromosomal gene vvp plays a role in the initial steps of infection, the VSE strain CECT4999, the cured strain CT218 and the Vvp-deficient mutant CT201 (obtained in this work by allelic exchange) were used in colonization and virulence experiments. The eel avirulent biotype 1 (BT1) strain YJ016, whose genome has been sequenced, was used for comparative purposes. The global results demonstrate that the plasmid does not play a significant role in surface colonization because (i) CECT4999 and CT218 were equally chemoattracted towards and adherent to eel mucus and gills, and (ii) CT218 persisted in gills from bath-infected eels 2 weeks post infection. In contrast, mutation in vvp gene reduced significantly chemoattraction and attachment to eel mucus and gills, as well as virulence degree by immersion challenge. Co-infection experiments by bath with CECT4999 and CT201 confirmed that Vvp was involved in eel colonization and persistence in gills, because CECT4999 was recovered at higher numbers compared with CT201 from both internal organs of moribund fish (ratio 4:1) and gills from survivors (ratio 50:1). Interestingly, YJ016 also showed chemoattraction and attachment to mucus, and complementation of CT201 with BT1-vvp gene restored both activities together with virulence degree by immersion challenge. Additional experiments with algae mucus and purified mucin gave similar results. In conclusion, the protease Vvp of V. vulnificus seems to play an essential role in colonization of mucosal surfaces present in aquatic environments. Among the V. vulnificus strains colonizing fish mucus, only those harbouring the plasmid could survive in blood and cause septicaemia.

The N-terminal propeptide of Vibrio vulnificus extracellular metalloprotease is both an inhibitor of and a substrate for the enzyme

Vibrio vulnificus, a marine bacterium capable of causing wound infection and septicemia, secretes a 45-kDa metalloprotease (vEP) with many biological activities. The precursor of vEP consists of four regions: a signal peptide, an N-terminal propeptide (nPP), a C-terminal propeptide, and the mature protease. Two forms of vEP-vEP-45, which contains the mature protease plus the C-terminal propeptide, and vEP-34, which contains only the mature protease-were expressed in Escherichia coli and purified. vEP-45 and vEP-34 had similar activities with azocasein as a substrate, but vEP-34 had reduced activity toward insoluble proteins. The nPP of vEP was expressed as a His tag fusion protein, and its effect on vEP activity was investigated. nPP inhibited the activities of both vEP-45 and vEP-34 but not that of thermolysin, a different but related zinc-dependent protease. The inhibition of vEP by nPP was further examined using vEP-34 as a representative enzyme. The inhibition could be completely reversed under conditions of low enzyme and propeptide concentrations and with prolonged incubation, which resulted from the degradation of nPP by vEP. However, even at high nPP and vEP concentrations, inhibition of vEP by nPP at high temperatures was not effective, resulting in the degradation of both nPP and vEP. These results demonstrate that the nPP of vEP could bind to vEP and inhibit its activity, resulting in the degradation of the propeptide.

Production of Vibrio vulnificus metalloprotease VvpE begins during the early growth phase: Usefulness of gelatin-zymography

Recent studies have demonstrated that expression of the vvpE gene begins during the early growth phase albeit at low levels. However, we found that the traditional protease assay method that is used to measure caseinolytic activity in culture supernatants is not suitable for the measurement of extracellular VvpE that is produced at low levels during the early growth phase. By using gelatin-zymography in place of the protease assay, we could specifically detect only VvpE of several proteases produced by Vibrio vulnificus. Moreover, we could sensitively measure VvpE produced at low levels during the early growth phase, which was consistent with transcription of the vvpE gene. The extracellular production of VvpE was reduced or delayed by mutation of the pilD gene which encodes for the type IV leader peptidase/N-methyltransferase associated with the type II general secretion system; the delayed production of VvpE was recovered by in trans complementation of the wild-type pilD gene. These results indicate that VvpE begins to be produced during the early growth phase via the PilD-mediated type II general secretion system, and that the use of gelatin-zymography is recommended as a simple method for the sensitive and specific detection of VvpE production.

Phospholipid directed motility of surface-motile bacteria

Myxococcus xanthus is a surface-motile bacterium that has adapted at least one chemosensory system to allow directed movement towards the slowly diffusible lipid phosphatidylethanolamine (PE). The Dif chemosensory pathway is remarkable because it has at least three inputs coupled to outputs that control extracellular matrix (ECM) production and lipid chemotaxis. The methyl-accepting chemotaxis protein, DifA, has two different sensor inputs that have been localized by mutagenesis. The Dif chemosensory pathway employs a novel protein that slows adaptation. Lipid chemotaxis may play important roles in the M. xanthus life cycle where prey-specific and development-specific attractants have been identified. Lipid chemotaxis may also be an important mechanism for locating nutrients by lung pathogens such as Pseudomonas aeruginosa.

Characterization of a recombinantly expressed proteinase K-like enzyme from a psychrotrophic Serratia sp

The gene encoding a peptidase that belongs to the proteinase K family of serine peptidases has been identified from a psychrotrophic Serratia sp., and cloned and expressed in Escherichia coli. The gene has 1890 base pairs and encodes a precursor protein of 629 amino acids with a theoretical molecular mass of 65.5 kDa. Sequence analysis suggests that the peptidase consists of a prepro region, a catalytic domain and two C-terminal domains. The enzyme is recombinantly expressed as an active approximately 56 kDa peptidase and includes both C-terminal domains. Purified enzyme is converted to the approximately 34 kDa form by autolytic cleavage when incubated at 50 degrees C for 30 min, but retains full activity. In the present work, the Serratia peptidase (SPRK) is compared with the family representative proteinase K (PRK) from Tritirachium album Limber. Both enzymes show a relatively high thermal stability and a broad pH stability profile. SPRK possess superior stability towards SDS at 50 degrees C compared to PRK. On the other hand, SPRK is considerably more labile to removal of calcium ions. The activity profiles against temperature and pH differ for the two enzymes. SPRK shows both a broader pH optimum as well as a higher temperature optimum than PRK. Analysis of the catalytic properties of SPRK and PRK using the synthetic peptide succinyl-Ala-Ala-Pro-Phe-pNA as substrate showed that SPRK possesses a 3.5-4.5-fold higher kcat at the temperature range 12-37 degrees C, but a fivefold higher Km results in a slightly lower catalytic efficiency (kcat/Km) of SPRK compared to PRK.

The eel immune system: present knowledge and the need for research

The European eel, Anguilla anguilla, is one of the most important warm water fish species cultured in southern Europe and the Mediterranean as well as in northern countries including Germany, the Netherlands and Denmark. The Japanese eel, A. japonica, is an important cultured fish in several Asiatic countries including Japan, China and Taiwan. During recent decades, research has been performed to elucidate the immune response of these species against different pathogens (viruses, bacteria or parasites). Nevertheless, there is very limited information in terms of both cellular and humoral immune responses. This review summarizes the present knowledge relating to the eel immune system and includes new data.

Molecular Cloning of the Gene Encoding Vibrio Metalloproteinase Vimelysin and Isolation of a Mutant with High Stability in Organic Solvents

Vimelysin is a unique metalloproteinase from Vibrio sp. T1800 exhibiting high activity at low temperature and high stability in organic solvents such as ethanol. A 1,821 bp open reading frame of the vimelysin gene encoded 607 amino acid residues consisting of an N-terminal pro-region, a mature enzyme, and a C-terminal pro-region. The mature enzyme region showed 80%, 57% and 35% sequence identity with the mature forms of vibriolysin from V. vulnificus, pseudolysin from Pseudomonas aeruginosa, and thermolysin from Bacillus thermoproteolyticus, respectively. The catalytic residues and zinc-binding motifs of metalloproteinases are well conserved in vimelysin. The vimelysin gene was expressed in E. coli JM109 cells and the recombinant enzyme was purified as a 38-kDa mature form from cell-free extracts. The purified recombinant enzyme is indistinguishable from the enzyme purified directly from Vibrio. To obtain mutants exhibiting higher stability in organic solvents, random mutations were introduced by error-prone PCR and 600 transformants were screened. The N123D mutant exhibits two times higher stability in organic solvents than the wild-type enzyme. A plausible mechanism for the stability of the N123D mutant in organic solvents was discussed based on homology models of vimelysin and the N123D mutant.

Vibrio vulnificus secretes a broad-specificity metalloprotease capable of interfering with blood homeostasis through prothrombin activation and fibrinolysis

Vibrio vulnificus is a causative agent of serious food-borne diseases in humans related to the consumption of raw seafood. It secretes a metalloprotease that is associated with skin lesions and serious hemorrhagic complications. In this study, we purified and characterized an extracellular metalloprotease (designated as vEP) having prothrombin activation and fibrinolytic activities from V. vulnificus ATCC 29307. vEP could cleave various blood clotting-associated proteins such as prothrombin, plasminogen, fibrinogen, and factor Xa, and the cleavage could be stimulated by addition of 1 mM Mn2+ in the reaction. The cleavage of prothrombin produced active thrombin capable of converting fibrinogen to fibrin. The formation of active thrombin appeared to be transient, with further cleavage resulting in a loss of activity. The cleavage of plasminogen, however, did not produce an active plasmin. vEP could cleave all three major chains of fibrinogen without forming a clot. It could cleave fibrin polymer formed by thrombin as well as the cross-linked fibrin formed by factor XIIIa. In addition, vEP could also cleave plasma proteins such as bovine serum albumin and gamma globulin, and its broad specificity is reflected in the cleavage sites, which include Asp207-Phe208 and Thr272-Ala273 bonds in prothrombin and a Tyr80-Leu81 bond in plasminogen. Taken together, the data suggest that vEP is a broad-specificity protease that could function as a prothrombin activator and a fibrinolytic enzyme to interfere with blood homeostasis as part of the mechanism associated with the pathogenicity of V. vulnificus in humans and thereby facilitate the development of systemic infection.

Pathogenic Factors of Vibrios with Special Emphasis on Vibrio vulnificus

Bacteria of the genus Vibrio are normal habitants of the aquatic environment and play roles for biocontrole of aquatic ecosystem, but some species are believed to be human pathogens. These species can be classified into two groups according to the types of diseases they cause: the gastrointestinal infections and the extraintestinal infections. The pathogenic species produce various pathogenic factors including enterotoxin, hemolysin, cytotoxin, protease, siderophore, adhesive factor, and hemagglutinin. We studied various pathogenic factors of vibrios with special emphasis on protease and hemolysin of V. vulnificus. V. vulnificus is now recognized as being among the most rapidly fatal of human pathogens, although the infection is appeared in patients having underlying disease(s) such as liver dysfunction, alcoholic cirrhosis or haemochromatosis. V. vulnificus protease (VVP) is thought to be a major toxic factor causing skin damage in the patients having septicemia. VVP is a metalloprotease and degrades a number of biologically important proteins including elastin, fibrinogen, and plasma proteinase inhibitors of complement components. VVP causes skin damages through activation of the Factor XII-plasma kallikrein-kinin cascade and/or exocytotic histamine release from mast cells, and a haemorrhagic lesion through digestion of the vascular basement membrane. Thus, the protease is the most probable candidate for tissue damage and bacterial invasion during an infection. Pathogenic roles and functional mechanism of other factors including hemolysins of V. vulnificus and V. mimicus are also shown in this review article.

Generation of active fragments from human zymogens in the brady kinin-generating cascade by extracellular proteases from Vibrio vulnificus and V. parahaemolyticus

Vibrio vulnificus is an opportunistic human pathogen causing septicemia, and the infection is characterized by formation of the edematous skin lesions on limbs. This pathogenic species secretes a thermolysin-like metalloprotease as a virulence determinant. The metalloprotease was confirmed to activate human factor XII-plasma kallikrein-kinin cascade that results in liberation of bradykinin, a chemical mediator enhancing the vascular permeability, from high-molecular weight kininogen. Namely, the metalloprotease showed to generate active fragments by cleavage of Arg-Ile, Arg-Val or Gly-Leu peptide bond in human zymogens (plasma prekallikrein and factor XII). In spite of induction of the sufficient vascular permeability-enhancing and edema-forming reaction in the guinea pig model, a serine protease from V. parahaemolyticus, a human pathogen causing primarily watery diarrhea, showed far less ability to activate and to cleave the human zymogens. These results in part may explain why only V. vulnificus often causes serious edematous skin damages in humans.

Transcriptional regulation of Vibrio cholerae hemagglutinin/protease by the cyclic AMP receptor protein and RpoS

Vibrio cholerae secretes a Zn-dependent metalloprotease, hemagglutinin/protease (HA/protease), which is encoded by hapA and displays a broad range of potentially pathogenic activities. Production of HA/protease requires transcriptional activation by the quorum-sensing regulator HapR. In this study we demonstrate that transcription of hapA is growth phase dependent and specifically activated in the deceleration and stationary growth phases. Addition of glucose in these phases repressed hapA transcription by inducing V. cholerae to resume exponential growth, which in turn diminished the expression of a rpoS-lacZ transcriptional fusion. Contrary to a previous observation, we demonstrate that transcription of hapA requires the rpoS-encoded sigma(s) factor. The cyclic AMP (cAMP) receptor protein (CRP) strongly enhanced hapA transcription in the deceleration phase. Analysis of rpoS and hapR mRNA in isogenic CRP+ and CRP- strains suggested that CRP enhances the transcription of rpoS and hapR. Analysis of strains containing hapR-lacZ and hapA-lacZ fusions confirmed that hapA is transcribed in response to concurrent quorum-sensing and nutrient limitation stimuli. Mutations inactivating the stringent response regulator RelA and the HapR-controlled AphA regulator did not affect HA/protease expression. Electrophoretic mobility shift experiments showed that pure cAMP-CRP and HapR alone do not bind the hapA promoter. This result suggests that HapR activation of hapA differs from its interaction with the aphA promoter and could involve additional factors.

Immunogenic antigens of the eel pathogen Vibrio vulnificus serovar E

The immunogenic antigens of Vibrio vulnificus serovar E were investigated in the eel. Fish were vaccinated by immersion with Vulnivaccine (V), revaccinated 2 years later by intraperitoneal injection (RV) and bath infected 15 days post-revaccination (RVI). The specific immune response in serum was followed in all groups, and selected sera were used for immunostaining of surface (SA) and extracellular antigens (ECA). Bacteria were grown in iron-rich (TSB and MSWYE) and iron-poor media (TSB and MSWYE plus human transferrin (TSB-T and MSWYE-T)) as well as eel serum (ES), and their SA and ECA were extracted and electrophoretically analysed. Cells grown in MSWYE-T and ES presented the same antigenic profiles, which suggests that iron-restriction is the main growth-limiting factor in vivo. The electrophoretic pattern of SA, but not that of ECA, varied with iron-availability in the growth medium. Further, SA extracted from bacteria grown in iron restriction were strongly immunogenic for eels, especially after vaccination and infection. Among the immunogenic antigens over expressed in iron-restriction, three outer membrane proteins of around 70-80 kDa, including the putative receptor for vulnibactin, together with the rapid and slow migrating forms of the lipopolysaccharide (LPS), were identified. The response was not so evident in the case of capsule, which was not clearly stained with any of the eel sera. With respect to ECA, two proteins, identified as the V. vulnificus protease (Vvp) and the major outer membrane protein (OMP), probably liberated to the medium after cell death, were recognised by RV and, more strongly, by RVI sera. The specific antibodies against the mentioned OMPs, LPS bands and the Vvp may contribute to the protection of vaccinated eels against infection, giving a reasonable explanation for the high effectiveness of Vulnivaccine.

The role and regulation of the extracellular proteases of Staphylococcus aureus

Staphylococcus aureus has several extracellular proteases with proposed roles in virulence. SspA (serine protease), SspB (cysteine protease) and Aur (metalloprotease) have been characterized previously and SspA and SspB were found to be cotranscribed. The coding region for the cysteine protease ScpA has been identified and characterized. It is in a probable bi-cistronic operon with scpA located immediately upstream of a coding region for a 108 aa protein that is a specific inhibitor of ScpA. Using primer extension analysis promoters have been mapped and it was found that sigmaA is the only sigma factor involved in the transcription of scpA, sspABC and aur. The transcription of all the genes occurs maximally at post-exponential phase, being positively regulated by agr (accessory gene regulator) and negatively regulated by sarA (staphylococcal accessory regulator). Furthermore sigmaB represses transcription from the aur and scp operons similarly to the previously shown effect on ssp [Horsburgh, M., Aish, J., White, I., Shaw, L., Lithgow, J. & Foster, S. (2002). J Bacteriol 184, 5457-5467]. Using mutations in each protease gene the proteolytic cascade of activation has been analysed. Aur, SspA, SspB and ScpA are all produced as zymogens, activated by proteolytic cleavage. Although the metalloprotease, Aur, does catalyse activation of the SspA zymogen, it is not the sole agent capable of conducting this process. Site-directed mutagenesis revealed that Aur is not capable of undergoing auto-proteolysis to achieve activation. The cysteine protease, ScpA, appears to reside outside this cascade of activation, as mature ScpA was observed in the aur, sspA and sspB mutant strains. Using a mouse abscess model, it has been shown that insertional inactivation of sspA or sspB results in significant attenuation of virulence, whilst mutations in aur or scpA do not. It is likely the attenuation observed in the sspA strain is due to polarity on the sspB gene.

High growing ability of Vibrio vulnificus biotype 1 is essential for production of a toxic metalloprotease causing systemic diseases in humans

Vibrio vulnificus biotype 1, a causative agent of fatal septicemia or wound infection in humans, is known to produce a toxic metalloprotease as an important virulence determinant. V. vulnificus biotype 2 (serovar E), a primary eel pathogen, was found to elaborate an extracellular metalloprotease that was indistinguishable from that of biotype 1. The potential of V. vulnificus biotype 1 for production of the metalloprotease was compared with biotype 2 and other human non-pathogenic Vibrio species (Vibrio anguillarum and Vibrio proteolyticus). When cultivated at 25 degrees C in tryptone-yeast extract broth supplemented with 0.9% NaCl, all bacteria multiplied sufficiently and secreted significant amounts of the metalloprotease. However, at 37 degrees C with 0.9% NaCl, V. anguillarum neither grew nor produced the metalloprotease. In human serum, only V. vulnificus biotype 1 revealed a steady multiplication accompanied with production of the extracellular metalloprotease. This prominent ability of biotype 1 in growth and protease production may contribute to cause serious systemic diseases in humans.

SmcR and cyclic AMP receptor protein coactivate Vibrio vulnificus vvpE encoding elastase through the RpoS-dependent promoter in a synergistic manner

The putative virulence factors of Vibrio vulnificus include an elastase, the gene product of vvpE. We previously demonstrated that vvpE expression is differentially directed by two different promoters in a growth phase-dependent manner. The activity of the stationaryphase promoter (promoter S (PS)) is dependent on RpoS and is also under the positive control of cyclic AMP receptor protein (CRP). In this study, primer extension analyses revealed that SmcR, the Vibrio harveyi LuxR homolog, is also involved in the regulation of vvpE transcription by activating PS. Although the influence of CRP on PS is mediated by SmcR, the level of PS activity observed when CRP and SmcR function together was found to be greater than the sum of the PS activities achieved by each activator alone. Western blot analyses demonstrated that the cellular levels of RpoS, CRP, and SmcR were not significantly affected by one other, indicating that CRP and SmcR function cooperatively to activate PS rather than sequentially in a regulatory cascade. The binding sites for CRP and SmcR were mapped based on a deletion analysis of the vvpE promoter region and confirmed by in vitro DNase I protection assays. The binding sites for CRP and SmcR were juxtapositioned and centered 220 and 198 bp upstream of the transcription start site of PS, respectively. Accordingly, these results reveal that CRP and SmcR function synergistically to coactivate the expression of vvpE by the RpoS-dependent promoter (PS) and that the activators exert their effect by directly binding to the promoter in the stationary phase.

Isolation and characterization of a zinc-containing metalloprotease expressed by Vibrio tubiashii

A Vibrio tubiashii hemagglutinin, a protease, was purified by ammonium sulfate precipitation, gel filtration, and hydrophobic interaction chromatography. It agglutinates sheep, chicken, bovine, rabbit, guinea pig, and human erythrocytes. It has a molecular mass of 35 kDa, isoelectric points of 3.5 and 3.7, and is inhibited by ortho-phenanthro line, phosphoramidon, and Zincov. The N-terminal amino acid sequence (Ala-Gln-Ala-Thr-Gly-Thr-Gly- Pro-Gly-Gly-Asn-Gln-Lys-Thr-Gly-Gln- Tyr-Asn-Phe-Gly) has strong homology to other Vibrio proteases.Key words: Vibrio tubiashii, metalloprotease, hemagglutinin.

Characterization of the enzyme activity of an extracellular metalloprotease (VMC) from Vibrio mimicus and its C-terminal deletions

To investigate the enzymatic properties of Vibrio mimicus metalloprotease, the mature metalloprotease gene (vmc) was overexpressed in Escherichia coli and the recombinant protein (rVMC61) was purified by metal affinity chromatography. rVMC61 showed maximum activity at about 37 degrees C, pH 8. The purified rVMC61 was very specific toward collagen substrates, such as gelatin, type I, II, and III collagens and synthetic peptides (Cbz-GPLGP and Cbz-GPGGPA). But it did not show degrading activity toward other biological proteins including lysozyme, lactoferrin and bovine serum albumin. rVMC61 also showed cytotoxicity against CHSE-214 fish cells. To examine the role of the C-terminal region of rVMC61, the 3' end of the metalloprotease gene (vmc) was digested serially with exonuclease III. The truncated vmc derivatives encoding 57-42 kDa of the protease were isolated and overexpressed in E. coli. The collagenase activities of truncated proteins were investigated using gelatin as substrate. Deletion of 100 amino acids from the C-terminus resulted in loss of gelatin degrading activity. However, deletion of 67 amino acids from the C-terminus did not affect its gelatin degrading activity.