ABSTRACT
We have cloned, sequenced and analysed all the five classes of the intergenic (16S-23S rRNA) spacer region (ISR) associated with the eight rrn operons (rrna-rrnh) of Vibrio cholerae serogroup O1 El Tor strains isolated before, during and after the O 139 outbreak. ISR classes 'a' and 'g' were found to be invariant, ISR-B (ISRb and ISRe) exhibited very little variation, whereas ISR-C (ISRc, ISRd, and ISRf) and ISRh showed the maximum variation. Phylogenetic analysis conducted with all three ISR classes (ISR-B, ISR-C and ISRh) showed that the pre-O 139 serogroup and post-O 139 serogroup O1 El Tor strains arose out of two independent clones, which was congruent with the observation made by earlier workers suggesting that analyses of ISR-C and ISR-h, instead of all five ISR classes, could be successfully used to study phylogeny in this organism.
Subject(s)
Cloning, Molecular/methods , DNA, Intergenic/genetics , DNA, Ribosomal Spacer/genetics , Electrophoresis, Agar Gel , Genetic Heterogeneity , Genome, Bacterial/genetics , Molecular Sequence Data , Phylogeny , Polymerase Chain Reaction , RNA, Ribosomal, 16S/genetics , RNA, Ribosomal, 23S/genetics , Sequence Alignment , Sequence Analysis, DNA , Sequence Homology, Nucleic Acid , Vibrio cholerae O1/classification , Vibrio cholerae O139/classificationABSTRACT
Nine major transfer RNA (tRNA) gene clusters were analysed in various Vibrio cholerae strains. Of these, only the tRNA operon I was found to differ significantly in V. cholerae classical (sixth pandemic) and El Tor (seventh pandemic) strains. Amongst the sixteen tRNA genes contained in this operon, genes for tRNA Gln3 (CAA) and tRNA Leu6 (CUA) were absent in classical strains as compared to El Tor strains. The observation strongly supported the view that the above two pandemic strains constitute two different clones.
Subject(s)
Operon/genetics , RNA, Transfer/chemistry , Vibrio cholerae/classification , rRNA Operon/geneticsABSTRACT
Non-pathogenic, environmental strain of Vibrio cholerae, ELTOR Ogawa EW6 carries a copy of the cholera toxin gene in its chromosome. Restriction enzyme digestion followed by Southern blot analysis revealed that the structure of the cholera toxin gene in this organism is different from that found in the virulent strains. The xbaI site which has been found to be conserved in the cholera toxin of the virulent strains examined so far, is absent here. Results of the RNA dot blot analysis indicated that the cholera toxin gene in EW6 is transcribed much less efficiently compared to the cholera toxin gene present in the virulent strain Vibrio cholerae classical Inaba 569B.