Purification, characterization and molecular cloning of Vibrio fluvialis hemolysin

Purification and Characterization of the Lecithin-Dependent Thermolabile Hemolysin Vhe1 from the Vibrio sp. Strain MA3 Associated with Mass Mortality of Pearl Oyster (Pinctada fucata)

In a previous study, we isolated a Vibrio sp. strain MA3 and its virulence factor, a hemolysin encoded by vhe1. This strain is associated with mass mortalities of the pearl oyster Pinctada fucata. In the present study, the vhe1 gene from strain MA3 was cloned and its encoded product was purified and characterized. Our results show that the vhe1 gene encodes a protein of 417 amino acids with an estimated molecular mass of 47.2 kDa and a pI of 5.14. The deduced protein, Vhe1, was found to contain the conserved amino acid sequence (GDSL motif) of the hydrolase/esterase superfamily and five conserved blocks characteristic of SGNH hydrolases. A BLAST homology search indicated that Vhe1 belongs the lecithin-dependent hemolysin/thermolabile hemolysin (LDH/TLH) family. In activity analyses, the optimal temperature for both the hemolytic and phospholipase activities of Vhe1 was 50 °C. Vhe1 hemolytic activity and phospholipase activity were highest at pH 8.5 and pH 8.0, respectively. However, both enzymatic activities sharply decreased at high temperature (> 50 °C) and pH < 7.0. Compared with previously reported hemolysins, Vhe1 appeared to be more thermal- and pH-labile. Both its hemolytic activity and phospholipase activity were significantly inhibited by CuCl2, CdCl2, ZnCl2, and NiCl2, and slightly inhibited by MnCl2 and CoCl2. Vhe1 showed higher phospholipase activity toward medium-chain fatty acids (C8-C12) than toward shorter- and longer-chain fatty acids. These results accumulate knowledge about the LDH/TLH of V. alginolyticus, which detailed characterization has not been reported, and contribute to solving of the mass mortality of pearl oyster.

Metal Ions and Chemical Modification Reagents Inhibit the Enzymatic Activity of Lecithin-Dependent Hemolysin from Vibrio parahaemolyticus

Lecithin-dependent thermolabile hemolysin (LDH) is a virulence factor excreted by Vibrio parahaemolyticus, a marine bacterium that causes important losses in shrimp farming. In this study, the function of LDH was investigated through its inhibition by metal ions (Mg2+, Ca2+, Mn2+, Co2+, Ni2+ and Cu2+) and chemical modification reagents: β-mercaptoethanol (βME), phenylmethylsulfonyl fluoride (PMSF) and diethyl pyrocarbonate (DEPC). LDH was expressed in the Escherichia coli strain BL-21, purified under denaturing conditions, and the enzymatic activity was evaluated. Cu2+, Ni2+, Co2+ and Ca2+ at 1 mmol/L inhibited the LDH esterase activity by 20−95%, while Mg2+ and Mn2+ slightly increased its activity. Additionally, PMSF and DEPC at 1 mmol/L inhibited the enzymatic activity by 40% and 80%, respectively. Dose-response analysis showed that DEPC was the best-evaluated inhibitor (IC50 = 0.082 mmol/L), followed by Cu2+ > Co2+ > Ni2+ and PMSF (IC50 = 0.146−1.5 mmol/L). Multiple sequence alignment of LDH of V. parahaemolyticus against other Vibrio species showed that LDH has well-conserved GDSL and SGNH motifs, characteristic of the hydrolase/esterase superfamily. Additionally, the homology model showed that the conserved catalytic triad His-Ser-Asp was in the LDH active site. Our results showed that the enzymatic activity of LDH from V. parahaemolyticus was modulated by metal ions and chemical modification, which could be related to the interaction with catalytic amino acid residues such as Ser153 and/or His 393.

Population genomics of the food-borne pathogen Vibrio fluvialis reveals lineage associated pathogenicity-related genetic elements

Vibrio fluvialis is a food-borne pathogen with epidemic potential that causes cholera-like acute gastroenteritis and sometimes extraintestinal infections in humans. However, research on its genetic diversity and pathogenicity-related genetic elements based on whole genome sequences is lacking. In this study, we collected and sequenced 130 strains of V. fluvialis from 14 provinces of China, and also determined the susceptibility of 35 of the strains to 30 different antibiotics. Combined with 52 publicly available V. fluvialis genomes, we inferred the population structure and investigated the characteristics of pathogenicity-related factors. The V. fluvialis strains exhibited high levels of homologous recombination and were assigned to two major populations, VflPop1 and VflPop2, according to the different compositions of their gene pools. VflPop2 was subdivided into groups 2.1 and 2.2. Except for VflPop2.2, which consisted only of Asian strains, the strains in VflPop1 and VflPop2.1 were distributed in the Americas, Asia and Europe. Analysis of the pathogenicity potential of V. fluvialis showed that most of the identified virulence-related genes or gene clusters showed high prevalence in V. fluvialis, except for three mobile genetic elements: pBD146, ICEVflInd1 and MGIVflInd1, which were scattered in only a few strains. A total of 21 antimicrobial resistance genes were identified in the genomes of the 182 strains analysed in this study, and 19 (90%) of them were exclusively present in VflPop2. Notably, the tetracycline resistance-related gene tet(35) was present in 150 (95%) of the strains in VflPop2, and in only one (4%) strain in VflPop1, indicating it was population-specific. In total, 91% of the 35 selected strains showed resistance to cefazolin, indicating V. fluvialis has a high resistance rate to cefazolin. Among the 15 genomes that carried the previously reported drug resistance-related plasmid pBD146, 11 (73%) showed resistance to trimethoprim-sulfamethoxazole, which we inferred was related to the presence of the dfr6 gene in the plasmid. On the basis of the population genomics analysis, the genetic diversity, population structure and distribution of pathogenicity-related factors of V. fluvialis were delineated in this study. The results will provide further clues regarding the evolution and pathogenic mechanisms of V. fluvialis, and improve our knowledge for the prevention and control of this pathogen.

Impact of a reduced water salinity on the composition of Vibrio spp. in recirculating aquaculture systems for Pacific white shrimp (Litopenaeus vannamei) and its possible risks for shrimp health and food safety

Tropical shrimp, like Litopenaeus vannamei, in land-based recirculating aquaculture systems (RAS) are often kept at low water salinities to reduce costs for artificial sea salt and the amount of salty wastewater. Although these shrimp are tolerant against low salinities, innate immunity suppression and changes in the microbial composition in the water can occur. As especially Vibrio spp. are relevant for shrimp health, alterations in the species composition of the Vibrio community were analysed in water from six RAS, run at 15‰ or 30‰. Additionally, pathogenicity factors including pirA/B, VPI, toxR, toxS, vhh, vfh, tdh, trh, flagellin genes and T6SS1/2 of V. parahaemolyticus were analysed. The Vibrio composition differed significantly depending on water salinity. In RAS at 15‰, higher numbers of the potentially pathogenic species V. parahaemolyticus, V. owensii and V. campbellii were detected, and especially in V. parahaemolyticus, various pathogenicity factors were present. A reduced salinity may therefore pose a higher risk of disease outbreaks in shrimp RAS. Because some of the detected pathogenicity factors are relevant for human health, this might also affect food safety. In order to produce healthy shrimp as a safe food for human consumption, maintaining high water salinities seems to be recommendable.

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.

Functional Characterization and Conditional Regulation of the Type VI Secretion System in Vibrio fluvialis

Vibrio fluvialis is an emerging foodborne pathogen of increasing public health concern. The mechanism(s) that contribute to the bacterial survival and disease are still poorly understood. In other bacterial species, type VI secretion systems (T6SSs) are known to contribute to bacterial pathogenicity by exerting toxic effects on host cells or competing bacterial species. In this study, we characterized the genetic organization and prevalence of two T6SS gene clusters (VflT6SS1 and VflT6SS2) in V. fluvialis. VflT6SS2 harbors three “orphan” hcp-vgrG modules and was more prevalent than VflT6SS1 in our isolates. We showed that VflT6SS2 is functionally active under low (25°C) and warm (30°C) temperatures by detecting the secretion of a T6SS substrate, Hcp. This finding suggests that VflT6SS2 may play an important role in the survival of the bacterium in the aquatic environment. The secretion of Hcp is growth phase-dependent and occurs in a narrow range of the growth phase (OD₆₀₀ from 1.0 to 2.0). Osmolarity also regulates the function of VflT6SS2, as evidenced by our finding that increasing salinity (from 170 to 855 mM of NaCl) and exposure to high osmolarity KCl, sucrose, trehalose, or mannitol (equivalent to 340 mM of NaCl) induced significant secretion of Hcp under growth at 30°C. Furthermore, we found that although VflT6SS2 was inactive at a higher temperature (37°C), it became activated at this temperature if higher salinity conditions were present (from 513 to 855 mM of NaCl), indicating that it may be able to function under certain conditions in the infected host. Finally, we showed that the functional expression of VflT6SS2 is associated with anti-bacterial activity. This activity is Hcp-dependent and requires vasH, a transcriptional regulator of T6SS. In sum, our study demonstrates that VflT6SS2 provides V. fluvialis with an enhanced competitive fitness in the marine environment, and its activity is regulated by environmental signals, such as temperature and osmolarity.

Erythrocyte lysis and Xenopus laevis oocyte rupture by recombinant Plasmodium falciparum hemolysin III

Malaria kills more than 1 million people per year worldwide, with severe malaria anemia accounting for the majority of the deaths. Malaria anemia is multifactorial in etiology, including infected erythrocyte destruction and decrease in erythrocyte production, as well as destruction or clearance of noninfected erythrocytes. We identified a panspecies Plasmodium hemolysin type III related to bacterial hemolysins. The identification of a hemolysin III homologue in Plasmodium suggests a potential role in host erythrocyte lysis. Here, we report the first characterization of Plasmodium falciparum hemolysin III, showing that the soluble recombinant P. falciparum hemolysin III is a pore-forming protein capable of lysing human erythrocytes in a dose-, time-, and temperature-dependent fashion. The recombinant P. falciparum hemolysin III-induced hemolysis was partially inhibited by glibenclamide, a known channel antagonist. Studies with polyethylene glycol molecules of different molecular weights indicated a pore size of approximately 3.2 nm. Heterologous expression of recombinant P. falciparum hemolysin III in Xenopus oocytes demonstrated early hypotonic lysis similar to that of the pore-forming aquaporin control. Live fluorescence microscopy localized transfected recombinant green fluorescent protein (GFP)-tagged P. falciparum hemolysin III to the essential digestive vacuole of the P. falciparum parasite. These transfected trophozoites also possessed a swollen digestive vacuole phenotype. Native Plasmodium hemolysin III in the digestive vacuole may contribute to lysis of the parasitophorous vacuole membrane derived from the host erythrocyte. After merozoite egress from infected erythrocytes, remnant P. falciparum hemolysin III released from digestive vacuoles could potentially contribute to lysis of uninfected erythrocytes to contribute to severe life-threatening anemia.

Vibrio fluvialis: an emerging human pathogen

Vibrio fluvialis is a pathogen commonly found in coastal environs. Considering recent increase in numbers of diarrheal outbreaks and sporadic extraintestinal cases, V. fluvialis has been considered as an emerging pathogen. Though this pathogen can be easily isolated by existing culture methods, its identification is still a challenging problem due to close phenotypic resemblance either with Vibrio cholerae or Aeromonas spp. However, using molecular tools, it is easy to identify V. fluvialis from clinical and different environmental samples. Many putative virulence factors have been reported, but its mechanisms of pathogenesis and survival fitness in the environment are yet to be explored. This chapter covers some of the major discoveries that have been made to understand the importance of V. fluvialis.

Synergistic and additive effects of chromosomal and plasmid-encoded hemolysins contribute to hemolysis and virulence in Photobacterium damselae subsp. damselae

Photobacterium damselae subsp. damselae causes infections and fatal disease in marine animals and in humans. Highly hemolytic strains produce damselysin (Dly) and plasmid-encoded HlyA (HlyA(pl)). These hemolysins are encoded by plasmid pPHDD1 and contribute to hemolysis and virulence for fish and mice. In this study, we report that all the hemolytic strains produce a hitherto uncharacterized chromosome-encoded HlyA (HlyAch). Hemolysis was completely abolished in a single hlyAch mutant of a plasmidless strain and in a dly hlyApl hlyAch triple mutant. We found that Dly, HlyA(pl), and HlyAch are needed for full hemolytic values in strains harboring pPHDD1, and these values are the result of the additive effects between HlyApl and HlyAch, on the one hand, and of the synergistic effect of Dly with HlyApl and HlyAch, on the other hand. Interestingly, Dly-producing strains produced synergistic effects with strains lacking Dly production but secreting HlyA, constituting a case of the CAMP (Christie, Atkins, and Munch-Petersen) reaction. Environmental factors such as iron starvation and salt concentration were found to regulate the expression of the three hemolysins. We found that the contributions, in terms of the individual and combined effects, of the three hemolysins to hemolysis and virulence varied depending on the animal species tested. While Dly and HlyApl were found to be main contributors in the virulence for mice, we observed that the contribution of hemolysins to virulence for fish was mainly based on the synergistic effects between Dly and either of the two HlyA hemolysins rather than on their individual effects.

Vibrio fluvialis in patients with diarrhea, Kolkata, India

We identified 131 strains of Vibrio fluvialis among 400 nonagglutinating Vibrio spp. isolated from patients with diarrhea in Kolkata, India. For 43 patients, V. fluvialis was the sole pathogen identified. Most strains harbored genes encoding hemolysin and metalloprotease; this finding may contribute to understanding of the pathogenicity of V. fluvialis.

The virulence phenotypes and molecular epidemiological characteristics of Vibrio fluvialis in China

Background

Vibrio fluvialis is considered to be an emerging foodborne pathogen and has been becoming a high human public health hazard all over the world, especially in coastal areas of developing countries and regions with poor sanitation. The distribution of virulence factors, microbiological and molecular epidemiological features of V. fluvialis isolates in China remains to be examined.

Methods and results

PCR targeted at the virulence determinants and phenotype tests including metabolism, virulence and antibiotic susceptibility were performed. Pulsed-field gel electrophoresis (PFGE) analysis was used to access the relatedness of isolates. A strain with deletion of the arginine dihydrolase system was first reported and proved in molecular level by PCR. Virulence genes vfh, hupO and vfpA were detected in all strains, the ability to produce hemolysin, cytotxin, protease and biofilm formation varied with strains. High resistance rate to β-lactams, azithromycin and sulfamethoxazole were observed. Twenty-seven percent of test strains showed resistant to two and three antibiotics. PFGE analysis demonstrated great genetic heterogeneity of test V. fluvialis strains.

Conclusion

This study evaluated firstly the biological characteristics and molecular epidemiological features of V. fluvialis in China. Some uncommon biochemical characteristics were found. Virulence genes were widely distributed in the isolates from patient and seafood sources, and the occurrence of virulence phenotypes varied with strains. Continued and enhanced laboratory based-surveillance is needed in the future together with systematically collection of the epidemiological information of the cases or the outbreaks.

First report of an anti-tumor, anti-fungal, anti-yeast and anti-bacterial hemolysin from Albizia lebbeck seeds

A monomeric 5.5-kDa protein with hemolytic activity toward rabbit erythrocytes was isolated from seeds of Albizia lebbeck by using a protocol that involved ion-exchange chromatography on Q-Sepharose and SP-Sepharose, hydrophobic interaction chromatography on Phenyl-Sepharose, and gel filtration on Superdex 75. It was unadsorbed on both Q-Sepharose and SP-Sepharose, but adsorbed on Phenyl-Sepharose. Its hemolytic activity was fully preserved in the pH range 0-14 and in the temperature range 0-100 °C, and unaffected in the presence of a variety of metal ions and carbohydrates. The hemolysin reduced viability of murine splenocytes and inhibited proliferation of MCF-7 breast cancer cells and HepG2 hepatoma cells with an IC₅₀ of 0.21, 0.97, and 1.37 μM, respectively. It impeded mycelial growth in the fungi Rhizoctonia solani with an IC₅₀ of 39 μM but there was no effect on a variety of other filamentous fungi, including Fusarium oxysporum, Helminthosporium maydis, Valsa mali and Mycosphaerella arachidicola. Lebbeckalysin inhibited growth of Escherichia coli with an IC₅₀ of 0.52 μM.

Vibrio fluvialis: an unusual enteric pathogen of increasing public health concern

In developing countries, the fraction of treated wastewater effluents being discharged into watersheds have increased over the period of time, which have led to the deteriorations of the qualities of major rivers in developing nations. Consequently, high densities of disease causing bacteria in the watersheds are regularly reported including incidences of emerging Vibrio fluvialis. Vibrio fluvialis infection remains among those infectious diseases posing a potentially serious threat to public health. This paper addresses the epidemiology of this pathogen; pathogenesis of its disease; and its clinical manifestations in humans.

Schizolysin, a hemolysin from the split gill mushroom Schizophyllum commune

Abstract A monomeric hemolysin with a molecular mass of 29 kDa was isolated from fresh fruiting bodies of the split gill mushroom Schizophyllum commune. The hemolysin was purified by successive adsorption on DEAE-cellulose, carboxymethyl-cellulose and Q-Sepharose and finally gel filtration on Superdex 75. This demonstrated the N-terminal sequence ATNYNKCPGA, different from those of previously reported fungal and bacterial hemolysins. The hemolysin was stable up to 40 degrees C. Only partial activity remained at 50 and 60 degrees C. Activity was indiscernible at 70 degrees C. A pH of 6.0 was optimal for activity. The hemolytic activity was most potently inhibited by dithiothreitol, sucrose and raffinose, followed by cellobiose, maltose, rhamnose, inulin, lactose, fructose and inositol. The metal ions Cu(2+), Mg(2+), Zn(2+), Al(3+) and Fe(3+) significantly, and Pb(2+) to a lesser extent, curtailed the activity of the hemolysin. The hemolysin inhibited HIV-1 reverse transcriptase with an IC(50) of 1.8 microM.

Identification of a Vibrio furnissii oligopeptide permease and characterization of its in vitro hemolytic activity

We describe purification and characterization of an oligopeptide permease protein (Hly-OppA) from Vibrio furnissii that has multifaceted functions in solute binding, in in vitro hemolysis, in antibiotic resistance, and as a virulence factor in bacterial pathogenesis. The solute-binding function was revealed by N-terminal and internal peptide sequences of the purified protein and was confirmed by discernible effects on oligopeptide binding, by accumulation of fluorescent substrates, and by fluorescent substrate-antibiotic competition assay experiments. The purified protein exhibited host-specific in vitro hemolytic activity against various mammalian erythrocytes and apparent cytotoxicity in CHO-K1 cells. Recombinant Hly-OppA protein and an anti-Hly-OppA monoclonal antibody exhibited and neutralized the in vitro hemolytic activity, respectively, which further confirmed the hemolytic activity of the gene product. In addition, a V. furnissii hly-oppA knockout mutant caused less mortality than the wild-type strain when it was inoculated into BALB/c mice, indicating the virulence function of this protein. Finally, the in vitro hemolytic activity was also confirmed with homologous ATP-binding cassette-type transporter proteins from other Vibrio species.

Overexpression, purification, characterization, and pathogenicity of Vibrio harveyi hemolysin VHH

Vibrio harveyi VHH hemolysin is a putative pathogenicity factor in fish. In this study, the hemolysin gene vhhA was overexpressed in Escherichia coli, and the purified VHH was characterized with regard to pH and temperature profiles, phospholipase activity, cytotoxicity, pathogenicity to flounder, and the signal peptide.

A hemolysin from the mushroom Pleurotus eryngii

A monomeric 17-kDa hemolysin designated as eryngeolysin was isolated from fresh fruiting bodies of the mushroom Pleurotus eryngii, using a protocol that involved gel filtration on Superdex 75, ion exchange chromatography on Mono Q and gel filtration on Superdex 75. Its N-terminal sequence demonstrated striking homology to that of its counterparts ostreolysin from the oyster mushroom Pleurotus ostreatus and aegerolysin from the mushroom Agrocybe cylindracea. Its hemolytic activity was unaffected over the pH range 4.0-12.0, but no activity was observed at pH 13 and at and below pH 2. The hemolysin was stable between 0 and 30 degrees C. At 40 degrees C, only residual activity was detectable. At and above 50 degrees C, activity was indiscernible. Eryngeolysin exhibited cytotoxicity toward leukemia (L1210) cells but not toward fungi. The hemolysin was inactivated by treatment with trypsin. It exhibited antibacterial activity against Bacillus sp. but not against other species. It inhibited basal as well as ConA-stimulated mitogenic response of murine splenocytes. N-Glycolyneuraminic acid was the only sugar capable of inhibiting the hemolytic activity. Eryngeolysin-induced hemolysis was osmotically protected by polyethylene glycol (PEG) 10000 with a mean hydrated diameter dose to 9.3 nm. However, no protection was offered by PEG 10000 to the anti-mitogenic and antiproliferative activities of eryngeolysin. The susceptibility of erythrocytes from different classes of vertebrates to eryngeolysin was mammalian > avian > reptilian > piscine.

Identification of an iron-regulated hemin-binding outer membrane protein, HupO, in Vibrio fluvialis: effects on hemolytic activity and the oxidative stress response

In pathogenic bacteria, iron acquisition is important for colonization and proliferation in the host under iron-limited conditions. The ability of Vibrio spp. to acquire iron is often critical to their virulence, causing gastroenteritis or excessive watery diarrhea in humans. In the study described here, we cloned the 2,100-bp heme utilization protein gene hupO in Vibrio fluvialis. HupO had high homology to iron-regulated outer membrane receptor proteins in Vibrio sp. and contained motifs that are common to bacterial heme receptors, including a consensus TonB box, a FRAP domain, and an NPNL domain. To characterize the hemin-binding activity of HupO, we purified the recombinant HupO protein (rHupO) from Escherichia coli by using an overexpression system. HupO was found to bind to hemin but not to hemoglobin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting demonstrated that the 77-kDa outer membrane protein HupO of V. fluvialis was induced under iron-restricted conditions. We constructed a hupO mutant, HP1, to investigate the biochemical function of HupO in V. fluvialis. The hemolytic activity of HP1 was reduced compared to that of wild-type cells and, when exposed to hydrogen peroxide, significantly lower numbers of HP1 survived than was the case in the wild type. These results suggest that HupO is associated with virulence expression in V. fluvialis through stimulation of hemolysin production and resistance to oxidative stress. In experimentally infected mice, the 50% lethal dose value of the wild-type was lower than that of the mutant, HP1.

Hemolysis of erythrocytes by granulysin-derived peptides but not by granulysin

Granulysin, a 9-kDa protein localized in human cytolytic T lymphocytes and natural killer cell granules, is cytolytic against tumors and microbes but not against red blood cells. Synthetic peptides corresponding to the central region of granulysin recapitulate the lytic activity of the intact molecule, and some peptides cause hemolysis of red blood cells. Peptides in which cysteine residues were replaced by serine maintain their activity against microbes but lose activity against human cells, suggesting their potential as antibiotics. Studies were undertaken to determine the mechanism of resistance of red blood cells to granulysin and sensitivity to a subset of granulysin-derived peptides. Granulysin lyses immature reticulocytes, which have mitochondria, but not red blood cells. Granulysin lyses U937 cells but not U937 cells lacking mitochondrial DNA and a functional respiratory chain (U937rho(o) degrees cells), further demonstrating the requirement of intact mitochondria for granulysin-mediated death. Peptide G8, which corresponds to helix 2/loop 2/helix 3, lyses red blood cells, while peptide G9, which is identical except that the cysteine residues were replaced by serine, does not lyse red blood cells. Granulysin peptide-induced hemolysis is markedly inhibited by an anion transporter inhibitor and by Na(+), K(+), and Ca(2+) channel blockers but not by Na(+)/K(+) pump, cotransport, or Cl(-) channel blockers. Although recombinant granulysin and G9 peptide do not induce hemolysis, they both competitively inhibit G8-induced hemolysis. The finding that some derivatives of granulysin are hemolytic may have important implications for the design of granulysin-based antimicrobial therapeutics.

The effect of merulinic acid on biomembranes

Merulinic acid (heptadecenylresorcinolic acid, resorcinolic acid) is one of the members of resorcinolic lipids, the natural amphiphilic long-chain homologues of orcinol (1,3-dihydroksy-5-methylbenzene). In the present study, membrane properties of merulinic acid were investigated. Merulinic acid exhibits strong haemolytic activity against sheep erythrocytes (EH50 of 5+/-2 microM) regardless of the form of its application-direct injection into the erythrocyte suspension or injection as merulinic acid-enriched liposomes. The lysis of erythrocytes induced by merulinic acid was inhibited by the presence of divalent cations. The effectivity of the protection of erythrocytes was highest for Zn2+ and weakest for Mn2+. Merulinic acid at low concentrations also exhibits the ability for protection of cells against their lysis in hypoosmotic solutions. This protective effect is significant as, at 10 microM concentration of merulinic acid, the extent of osmotically induced cell lysis is reduced by approximately 40%. Merulinic acid induces increased permeability of liposomal vesicles. This effect was shown to be dependent on the composition of liposomal bilayer and it was stronger when lipid bilayer contained glycolipids (MGDG and DGDG) and sphingomyelin. Changes of TMA-DPH and NBD-PE fluorescence polarization show that the degree of merulinic acid incorporation into liposomal membrane is not very high. The polar "heads" of the molecules of investigated compounds are localized on the level of fatty acid's ester bonds in phospholipid molecules. Merulinic acid caused the increased fluorescence of the membrane potential fragile probe. This indicated an alteration of the surface charge and a decrease of the local pH at the membrane surface. This effect was visible in both low- and high-ionic strength environment. Merulinic acid causes also a decrease in activity of the membrane-bound enzyme acetylcholinesterase.

Identification of oligopeptide permease (opp) gene cluster inVibrio fluvialisand characterization of biofilm production byoppAknockout mutation

Oligopeptides play important roles in bacterial nutrition and signaling. The oligopeptide permease (opp) gene cluster was cloned from Vibrio fluvialis. The V. fluvialis opp operon encodes five proteins: OppA, B, C, D and F. The deduced amino acid sequence of these proteins showed high similarity with those from other Gram-negative bacteria. To investigate whether OppA is involved in biofilm production, an oppA knockout mutant was constructed by homologous recombination. The oppA mutant produced more abundant biofilm than the wild type in BHI medium. When both strains were grown in minimal medium, we could not detect biofilm formation. However, it was found that the biofilm productivity of the oppA mutant was two folds greater than that of the wild type in minimal medium containing peptone or tryptone. This variation in biofilm production was demonstrated by scanning electron microscopy (SEM). In minimal medium containing C-sources, both strains produced some biofilm without significant difference in the biofilm productivity. Complementation of oppA gene with the plasmid pOAC2, which contains oppA ORF plus promoter regions, was sufficient to restore growth rate and biofilm to the wild type. These results suggest that the OppA protein is involved in uptake of peptides and affects biofilm productivity.