Aberrant gene for E1 Tor hemolysin from Vibrio cholerae non-O1, N037

Purification and characterization of enterotoxigenic El Tor-like hemolysin produced by Vibrio fluvialis

The halophilic bacterium Vibrio fluvialis is an enteric pathogen that produces an extracellular hemolysin. This hemolysin was purified to homogeneity by using sequential hydrophobic-interaction chromatography with phenyl-Sepharose CL-4B and gel filtration with Sephacryl S-200. It has a molecular weight of 63,000 and an isoelectric point of 4.6, and its hemolytic activity is sensitive to heat, proteases, and preincubation with zinc ions. The hemolysin lyses erythrocytes of the eight different animal species that we tested, is cytotoxic against Chinese hamster ovary cells in tissue culture, and elicits fluid accumulation in suckling mice. Lysis of erythrocytes occurs by a temperature-dependent binding step followed by a temperature- and pH-dependent lytic step. Fourteen of the first 20 N-terminal amino acid residues (Val-Ser-Gly-Gly-Glu-Ala-Asn-Thr-Leu-Pro-His-Val-Ala-Phe-Tyr-Ile-Asn-Val-Asn-Arg) are identical to those of the El Tor hemolysin of Vibrio cholerae and the heat-labile hemolysin of Vibrio mimicus. This homology was further confirmed by PCR analysis using a 5' primer derived from the amino-terminal sequence of the hemolysin and a 3' primer derived from the El Tor hemolysin structural gene. The hemolysin also reacts with antibodies to the El Tor-like hemolysin of non-O1 V. cholerae.

Cell vacuolation caused by Vibrio cholerae hemolysin

Non-O1 strains of Vibrio cholerae implicated in gastroenteritis and diarrhea generally lack virulence determinants such as cholera toxin that are characteristic of epidemic strains; the factors that contribute to their virulence are not understood. Here we report that at least one-third of diarrhea-associated nonepidemic V. cholerae strains from Mexico cause vacuolation of cultured Vero cells. Detailed analyses indicated that this vacuolation was related to that caused by aerolysin, a pore-forming toxin of Aeromonas; it involved primarily the endoplasmic reticulum at early times (approximately 1 to 4 h after exposure), and resulted in formation of large, acidic, endosome-like multivesicular vacuoles (probably autophagosomes) only at late times (approximately 16 h). In contrast to vacuolation caused by Helicobacter pylori VacA protein, that induced by V. cholerae was exacerbated by agents that block vacuolar proton pumping but not by endosome-targeted weak bases. It caused centripetal redistribution of endosomes, reflecting cytoplasmic alkalinization. The gene for V. cholerae vacuolating activity was cloned and was found to correspond to hlyA, the structural gene for hemolysin. HlyA protein is a pore-forming toxin that causes ion leakage and, ultimately, eukaryotic cell lysis. Thus, a distinct form of cell vacuolation precedes cytolysis at low doses of hemolysin. We propose that this vacuolation, in itself, contributes to the virulence of V. cholerae strains, perhaps by perturbing intracellular membrane trafficking or ion exchange in target cells and thereby affecting local intestinal inflammatory or other defense responses.

Two-step purification and partial characterization of a variant of the Vibrio cholerae non-O1 hemolysin

A two-step purification method using ammonium sulfate precipitation and gel filtration was developed for the purification of a variant of the El Tor hemolysin/cytolysin from supernatant fluids of a Vibrio cholerae non-O1 human isolate (strain 2194c). The toxin displayed delayed elution from a Sephacryl gel filtration column, eluting at between two and three column volumes. The molecular mass and isoelectric point of the purified 2194c toxin were 60 kDa and 5. 3, respectively. The N-terminal amino acid sequence was ASPAPANSETNTLPHVAFYI. Purified toxin was cytolytic for Chinese hamster ovary cells and erythrocytes from several animal species.

Genetic diversity and population structure of Vibrio cholerae

Multilocus enzyme electrophoresis (MLEE) of 397 Vibrio cholerae isolates, including 143 serogroup reference strains and 244 strains from Mexico and Guatemala, identified 279 electrophoretic types (ETs) distributed in two major divisions (I and II). Linkage disequilibrium was demonstrated in both divisions and in subdivision Ic of division I but not in subdivision Ia, which includes 76% of the ETs. Despite this evidence of relatively frequent recombination, clonal lineages may persist for periods of time measured in at least decades. In addition to the pandemic clones of serogroups O1 and O139, which form a tight cluster of four ETs in subdivision Ia, MLEE analysis identified numerous apparent clonal lineages of non-O1 strains with intercontinental distributions. A clone of serogroup O37 that demonstrated epidemic potential in the 1960s is closely related to the pandemic O1/O139 clones, but the nontoxigenic O1 Inaba El Tor reference strain is not. A strain of serogroup O22, which has been identified as the most likely donor of exogenous rfb region DNA to the O1 progenitor of the O139 clone, is distantly related to the O1/O139 clones. The close evolutionary relationships of the O1, O139, and O37 epidemic clones indicates that new cholera clones are likely to arise by the modification of a lineage that is already epidemic or is closely related to such a clone.

Nucleotide sequence of the vmhA gene encoding hemolysin from Vibrio mimicus

The structural gene (vmhA) of hemolysin from Vibrio mimicus (ATCC33653) was cloned and sequenced. The vmhA gene contains an open reading frame consisting of 2232 nucleotides which can code for a protein of 744 amino acids with a predicted molecular mass of 83,059. The similarity of amino acid sequence shows 81.6% identity with Vibrio cholerae El Tor hemolysin.

Biochemical and physiological characteristics of HlyA, a pore-forming cytolysin of Vibrio cholerae serogroup O1

Among the various toxins produced by the bacterial species Vibrio cholerae is HlyA, a cytolytic protein commonly called the E1 Tor hemolysin. HlyA is synthesized and processed in a complex manner involving various processed or degraded forms, that may co-purify and complicate the interpretation of biochemical and physiological experiments. In this study a single form of HlyA was purified by gel filtration and chromatofocusing using fast protein liquid chromatography in the presence of protease inhibitors. A 45-fold purification was obtained, with a final recovery of 17% of pure 60,000 mol. wt HlyA. A significant improvement in specific activity to 8.5 x 10(6) Chinese hamster ovary tissue culture units per mg protein was obtained. Physiological activity studies indicated that cytolysis of erythrocytes (hemolysis) was inhibited by oxygen: storage of HlyA under oil, and experimentation in N2-flushed buffers maintained activity. HlyA-mediated lysis of human erythrocytes was characterized by a significant lag phase, followed by a rapid induction of hemolysis. Hemolysis was inhibited by sucrose, an osmotic protectant, suggesting that the initial action of HlyA on erythrocytes is to raise the basal cation permeability of the cell membrane. The most likely cytolytic mechanism is thus the formation of transmembrane lesions such as homopolymer pores in target cells, as has been found for toxins from numerous other bacterial pathogens.