[Molecular characterization of Vibrio cholerae phage-type 6b epidemic isolates from 1998 to 2001 in Sichuan province].

OBJECTIVE: To investigate the molecular characteristics of phage-type 6b isolates emerging in 1998-2001 cholera epidemics in Sichuan province. METHODS: Isolates were analyzed by phage-typing, pulsed field gel electrophoresis (PFGE) and ompW gene sequencing. RESULTS: All phage-type 1b and 6b isolates in Sichuan province from 1998 to 2001 were toxigenic. A total of 24 patterns were identified after PFGE analysis, and one predominant pattern consisted of 13 isolates. Several 1b and 6b isolates from Sichuan and isolates of the 1b from other provinces showed the same PFGE pattern. Mutation in ompW gene was found in 6b isolates. CONCLUSION: V.cholerae O1 6b isolates in Sichuan province from 1998 to 2001 have special genetic markers, and might genetically correlate with contemporaneous 1b isolates.

[Sequence analysis of housekeeping genes recA, dnaE, and mdh in different serogroups or biotypes of Vibrio cholerae isolated from China].

OBJECTIVE: To analyze sequences of the housekeeping genes including recA, dnaE, and mdh in different serogroups or different biotypes of Vibrio cholerae (VC) strains isolated from China. METHODS AND RESULTS: recA, dnaE, and mdh genes of Vibrio cholerae were obtained by PCR, sequenced and analyzed. Forty-four variable bases were identified in the 500 bases of recA gene of 18 VC strains, and the mutation of only 3 variable bases could result in changes of 2 amino acids. In the 600 bases of dnaE genes of 18 strains, 32 variable bases were found and only 1 contributed to an amino acid change. In the 367 bases of mdh genes of 18 strains, only 1 variable base was identified whose mutation involved an amino acid convertion. Toxic EI Tor biotype (EVC) strains and toxic O139 serogroup strains were closely related. Non-toxic strains of different serogroups or types were lowly related. Non-toxic and toxic strains of different serogroups or types were lowly related. CONCLUSION: Toxic EVC and toxic O139 serogroup strains isolated from different areas of China may evolve from a common original strain, and toxic O139 VC strains may come from toxic EVC strains.

[Study on infection of different strains of Vibro cholerae O1 by El Tor CTXPhi].

To study the horizontal transfer efficiencies of filamentous bacteriophage CTXPhi in different V. cholera O1 strains and the phage immunities of these strains. The infectious El Tor CTXPhi particles genetic marked by chloramphenicol resistance gene were used to infect four different V. cholerae O1 strains in vivo and in vitro. Selected the infected clones based on its character of chloramphenicol resistance and identified and judged the exist form of CTXPhi genome through Southern bolt and other hybridization methods. Calculated the infection rates of different strains and compared each other. Then we analyzed the mechanism of infection and phage immunity. The infection rate of classic strain 1119 with the genetic marked CTX(ET)Phi in vivo is much higher than that in vitro. In vitro experiment, the rate of 1119 is higher than other three El Tor strains. And in El Tor strains, the infection frequency of IEM101 that had no rstR gene is 100 to 1000 times higher than other two strains containing rstR. Classical biotype strain is more susceptible to CTX(ET)Phi particles than El Tor strains. Expression of TCP and the phage immunity mediated by rstR gene affect the horizontal transfection of CTXPhi in V. cholerae strains.

[Sequence analysis of the mutated genes in CTXEVC Phi and nct-CTXnew Phi genomes in Vibrio cholerae JS94484 strain].

OBJECTIVE: To analyze the sequences of the mutated genes in CTX(EVC)Phi and nct-CTX(new)Phi genomes in Vibrio cholerae JS94484 strain. METHODS: The mutated genes in CTX(EVC)Phi and nct-CTX(new)Phi genome were obtained by PCR, sequenced and analyzed. RESULTS: ig1, rstR, ig2, and ctxAB genes in CTX(EVC)Phi genome of V. cholerae strain JS94484 were highly homologous with those of standard EVC strain N16961, while ig1, rstR and ig2 genes in nct-CTX(new)Phi genome of the strain JS94484 shared low homology with those of the other 3 biotypes of V. cholerae. Considerable difference was detected in the last 60 bp of zot genes between CTX(EVC)Phi and nct-CTX(new)Phi genomes, indicating possible difference in the amino sequences of the Zot proteins encoded by these two genes. The sequence of toxin-coregulated pilus A subunit gene (tcpA) of the strain JS94484 was identical with that of strain N16961. CONCLUSION: ig1, rstR and ig2 genes of nct-CTX(new)Phigenome are of a novel type, and their functions await further investigation.

[Functional analysis of promoters of Vibrio cholerea typing phage VP1 with reporter system].

Phage VP1 infects and lyses Vibrio cholerae. The VP1 genome is a circular double-strand DNA and its size is 32176 base pairs. Analysis of the sequence of the VP1 genome revealed the presence of 15 putative promoter sequence. The activities of these putative promoters in V. cholerae were assayed by transformation of reporter gene plasmid and phage infection together. Promoter regions were ligated into pRS1274/BamH I/EcoR I. Then transformed into E. coli JM109 and all of clone display blue. The recombinant plasmids were transformed into V. cholerae 7743 deltaZ by electroporation, then bacteriophage VP1 infect transformant. The time-course expressing lacZ gene and detecting change of beta-galactosidase enzyme activity in V. cholerae transformants at latent period, indicated P17 probably is a early promoter; P2 and P3 and P9 etc are medium-term promoters; P18 is a late promoter.

[Sequencing and analysis of Vibrio cholerae typing phage VP3 genome].

DNA sequence and the genome of phage VP3 (a typing phage of V. cholera) were analyzed. A random library of VP3 DNA was constructed by shot-gun library method. The VP3 genome sequence was assembled with contigs sequences, the gaps between different contigs were filled with sequencing data from primer walking. ORFs were predicted; Phylogeny of DNA polymerase sequences was analyzed to determine the class of VP3; The activity of putative promoter genes were analyzed using lacZ report system. VP3 genome is a 39504bp of circular double-stranded DNA. Twenty-seven out of forty-nine putative ORFs were annotated; twenty gene products were homologous with T7-like phages, including DNAP, DNA replicative protein, capsid, tail tubular, tail fiber protein, and DNA packaged protein. The activity of the putative promoter regions was confirmed through cloning those regions to LacZ-fuse plasmid pRS1274 and analysis of the expression of beta galactosidase. The complete genomic sequence of VP3 and phylogenetic tree analysis suggests VP3 is a member of T7 phage family.

[Analysis of gene cluster of Tat-dependent protein export system of Vibrio cholerae and its function].

The Tat (Twin-arginine translocatin) system is a recently defined protein export pathway that serves to translocate folded proteins. The substrates of the Tat pathway contain specific amino-terminal signal peptides that exhibit a conserved amino acid consensus motif-S/T-R-R-x-F-L-X. Here is the report of knocked out the tatA, tatB and tatC genes of the V. cholerae by suicide plasmid homologous recombination technology. Mutant strains showed obvious changes of growth characteristics. The transport of a typical Tat pathway substrate, trimethylamine N-oxide reductase (molybdoenzyme), was completely blocked. The physiochemical reactions of the parent and mutant strains were also analyzed. Four physiochemical reactions using D-galactose, L-asparagine, glyl-L-aspartic acid and D-L-alpha-glycerol phosphate as substrates were negative in mutant strains, which might be affected by the inactivation of the Tat-dependent system.