Molecular analysis of the rstR and orfU genes of the CTX prophages integrated in the small chromosomes of environmental Vibrio cholerae non-O1, non-O139 strains

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Abstract
Theud ctxABud genes encoding cholera toxin, reside in theud genome of a filamentous bacteriophage CTX φ .Theud presence of CTX prophage in non-epidemic environmentalud Vibrio cholerae strains is rare. The CTX prophage,ud the lysogenic form of CTX φ in V. cholerae , isud comprised of the ‘RS2’ and the ‘Core’. Analysis of theud rstR gene present in the RS2 region of the CTX prophageud revealed the presence of new alleles of the prophagesud in four environmental non-O1, non-O139 strainsud VCE22 (O36), VCE228 (O27), VCE232 (O4) and VCE233ud (O27), and the CTX prophages are located in the smallud chromosomes. Phylogenetic analysis based on theud nucleotide sequences of the rstR and orfU (present inud the core) genes of these prophages placed them in aud single unique cluster, which is distally located comparedud with that of epidemic V. cholerae O1 strains.ud Further analysis indicated that the genome of theud prophage present in the strain VCE22 is devoid of theud ctxAB genes, called pre-CTX prophage and the strainud also possess the toxin-coregulated pilus proteinud coding gene tcpA of classical type, another importantud pathogenicity determining locus of the epidemicud V. cholerae strains. Comparative analysis of theud nucleotide sequences of the rstR and orfU genes indicatedud that the pre-CTX prophage of VCE22 might b