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Examines the genetic variation of dtDP-L-rhamnose pathway genes in Salmonella enterica. Evidence of O antigen gene transfer; Role of rml genes in serogroup-specific gene subspecies transfer; Determination of gene cluster source.

Describes the use of deoxyribonucleic acid (DNA) hybridization and sequencing to show that the rough phenotype of Escherichia coli K12 strain is due to the presence of one of two independent mutations in the rfb gene cluster. Presence of the rfb-50 mutation in strain EMG2 and rfb-51 in strain EMG2; Production of O antigen.

The genetic variation in the dTDP-L-rhamnose pathway genes (rmlA, rmlB, rmlC and rmlD) in Vibrio cholerae was investigated. The genes are part of the O antigen gene cluster and the aim was to study lateral gene transfer of O antigen gene clusters. The rml genes of an 06 strain were cloned using an Escherichia coil K-12 strain designed for selecting cloned rml genes. Thirty-three strains carrying the known rhamnose-containing O antigens were probed with O6-based rml gene probes, and 19 were positive with from one to all four of the gene probes. Nine rml gene sets from this group were sequenced and found to be in the order rmlBADC, at the 5' end of the gene clusters. A gradient in the level of variation was observed, with highly similar sequences at the 5' end rmlB gene, but very divergent and strain-specific sequences at the 3' end of the rml gene set. The change in level of similarity varied in position, but was always abrupt and coincided with a change in GC content, indicating that the 5' and 3' parts are of different origin, and that recombination within rml genes has occurred. The rml gene sets of two of the strains that did not hybridize with any 06 rml gene probes were also cloned and sequenced. Both gene sets were in the middle of the O antigen gene cluster and were very divergent from each other and all other rml gene sets. This supports the hypothesis that presence of rml genes at the end of the O antigen gene cluster facilitates lateral gene transfer of rml-containing 0 antigen gene clusters in V. cholerae. The sequence relationships make it possible to identify sites of recombination and to distinguish DNA that has long been in V. cholerae and DNA that probably came into the species with the O antigen gene cluster. [ABSTRACT FROM AUTHOR]

The article discusses a group of Escherichia coli O serogroups and the Salmonella enterical serogroup O: 6, 14 (H), share a common four-sugar backbone O-subunit structure, and possess nearly identical O-antigen gene clusters. Results support the proposal that these serotypes have a common sugar backbone encoded by a conserved O-antigen gene cluster, with variation due to side branches encoded by genes located elsewhere in the genome.

The article presents a study on the structural and genetic evidence which claims that Escherichia coli O148 O antigen is the precursor of the shigella dysenteriae type 1 O antigen and identification of a glucosyltransferase gene. The study assesses that both bacteria have the same genes for O antigen synthesis with the same level of DNA identity as well as organization, however, shigella dysenteriae type 1 is interrupted by deletion and a glucosyltransferase gene.