O-antigen variation in Salmonella spp.: Rfb gene clusters of three strains

Department of Microbiology, University of Sydney, New South Wales, Australia.
Journal of Bacteriology (Impact Factor: 2.81). 02/1988; 170(1):103-7.
Source: PubMed


The O antigens of Salmonella serogroups A, B, and D differ structurally in their side-chain sugar residue. These genes encoding O-antigen biosynthesis are clustered in the rfb operon. We report here the molecular cloning and analysis of the rfb operons of Salmonella paratyphi A (serogroup A) and S. typhi (serogroup D). The regions of DNA nonhomology between the rfb operons of these serogroup A, B, and D representatives are identified, and the evolutionary derivation of serogroup A from a serogroup D progenitor is discussed.

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    • "The first was a frame shift mutation that generated a stop codon reducing the CDP-tyvelose epimerase to 5 residues, which would prevent conversion of CDP-Paratose to CDP-Tyvelose (Figure 3), and accounts for the presence of paratose in place of tyvelose, the only structural difference between the A and D1 O antigens. The other difference was a triplication of one segment, which led to an increased copy number of the wbaV gene, and generated a wbaU::wzx chimeric gene at the recombination site for the triplication [33] as shown in Figure 9. "
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    ABSTRACT: This paper covers eight Salmonella serogroups, that are defined by O antigens with related structures and gene clusters. They include the serovars that are now most frequently isolated. Serogroups A, B1, B2, C2-C3, D1, D2, D3 and E have O antigens that are distinguished by having galactose as first sugar, and not N-acetyl glucosamine or N-acetyl galactosamine as in the other 38 serogroups, and indeed in most Enterobacteriaceae. The gene clusters for these galactose-initiated appear to have entered S. enterica since its divergence from E. coli, but sequence comparisons show that much of the diversification occurred long before this. We conclude that the gene clusters must have entered S. enterica in a series of parallel events. The individual gene clusters are discussed, followed by analysis of the divergence for those genes shared by two or more gene clusters, and a putative phylogenic tree for the gene clusters is presented. This set of O antigens provides a rare case where it is possible to examine in detail the relationships of a significant number of O antigens. In contrast the more common pattern of O-antigen diversity within a species is for there to be only a few cases of strains having related gene clusters, suggesting that diversity arose through gain of individual O-antigen gene clusters by lateral gene transfer, and under these circumstances the evolution of the diversity is not accessible. This paper on the galactose-initiated set of gene clusters gives new insights into the origins of O-antigen diversity generally.
    Full-text · Article · Jul 2013 · PLoS ONE
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    • "The basic structures of the repeating units of serogroups A, B, and D are comprised of four sugars, three of which form a backbone (mannosyl–rhamnosyl–galactose). The fourth side chain sugar is the only variation among the three serogroups: abequose for serogroup B, tyvelose for serogroup D, and paratose for serogroup A (Verma et al., 1988). The rfbJ, rfbS, and rfbE genes are associated with the phenotypic differences of these serogroups (Liu, et al., 1991). "
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    ABSTRACT: Comparative genomic approaches provide abundant information to reveal the diversity among Salmonella serogroups. In a local genomic sequence database, twenty-five Salmonella whole genomic sequences were divided into 6 (A, B, C1, C2, D and others) serogroups for mining the DNA fragments specific for serogroups A through D. For each serogroup, a reference sequence was selected and split into 1000-bp fragments in silico to align against all the other genomic sequences to obtain one or more serogroup-specific fragments. As a result, 2, 6, 7, 10, and 7 specific fragments were found for A, B, C1, C2 and D serogroups, respectively. Specific primer sets targeting these DNA fragments were designed for multiplex PCR assays identifying 21 Salmonella standard strains and 86 additional food isolates. The PCR results demonstrated good agreement with those from Salmonella serotyping. This means that the PCR assay may be able to identify 5 (A, B, C1, C2 and D) Salmonella serogroups and elucidate differences among them. Based on the gene annotations, the 32 serogroup-specific fragments were divided into 3 categories (membrane protein genes, rfb gene clusters, and fimbrial genes). Each gene from these three groups was conserved within the serogroup and was closely correlated with phenotypic characterization. This finding implies that these genes, which are associated with sugar synthesis and metabolism or glycosyl and O-actetyl transfer, impart the differences among Salmonella serogroups.
    Full-text · Article · Jan 2011 · International journal of food microbiology
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    • "O antigen synthesis and assembly is encoded by the rfb gene cluster which typically contains 12 open reading frames, and ranges in size between serotypes, from approximately 8 kbp to 23 kbp. The variation of O antigens is not due to individual gene sequence variation, but rather to different sets of genes [1]. Approximately 20,000 repeating flagellin proteins polymerise to form the flagellar filament. "
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    ABSTRACT: The fliC and fljB genes in Salmonella code for the phase 1 (H1) and phase 2 (H2) flagellin respectively, the rfb cluster encodes the majority of enzymes for polysaccharide (O) antigen biosynthesis, together they determine the antigenic profile by which Salmonella are identified. Sequencing and characterisation of fliC was performed in the development of a molecular serotyping technique. FliC sequencing of 106 strains revealed two groups; the g-complex included those exhibiting "g" or "m,t" antigenic factors, and the non-g strains which formed a second more diverse group. Variation in fliC was characterised and sero-specific motifs identified. Furthermore, it was possible to identify differences in certain H antigens that are not detected by traditional serotyping. A rapid short sequencing assay was developed to target serotype-specific sequence motifs in fliC. The assay was evaluated for identification of H1 antigens with a panel of 55 strains. FliC sequences were obtained for more than 100 strains comprising 29 different H1 alleles. Unique pyrosequencing profiles corresponding to the H1 component of the serotype were generated reproducibly for the 23 alleles represented in the evaluation panel. Short read sequence assays can now be used to identify fliC alleles in approximately 97% of the 50 medically most important Salmonella in England and Wales. Capability for high throughput testing and automation give these assays considerable advantages over traditional methods.
    Full-text · Article · Sep 2004 · BMC Microbiology
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