Relationships among the rfb regions of Salmonella serovars A, B, and D

Abstract

The 0 antigens of Salmonella serogroups A, B, and D differ structurally in their side chain sugar residues.The genes encoding 0-antigen biosynthesis are clustered in the rib operon. The gene rjbj in strain LT2 (serovar typhimurium, group B) and the genes ribS and ribE in strain Ty2 (serovar typhi, group D) account for the known differences in the rfb gene clusters used for determination of group specificity. In this paper, we report the nucleotide sequence of 2.9 kb of DNA from the rjb gene cluster of strain Ty2 and the finding of two open reading frames which have limited similarity with the corresponding open reading frames of strain LT2. These two genes complete the sequence of the rib region of group D strain Ty2 if we use strain LT2 sequence where restriction site data show it to be extremely similar to the strain Ty2 sequence. The restriction map of the rib gene cluster in group A strain IMVS1316 (serovar paratyphi) is identical to that of the cluster in strain Ty2 except for a frameshift mutation in ribE and a triplicated region. The rib gene clusters of these three strains are compared, and the evolutionary origin of these genes is discussed.Lipopolysaccharide is a major component of the outer membrane of gram-negative bacteria that consists of three parts: lipid A, an oligosaccharide core, and oligosaccharide repeat units. In Salmonella enterica, the oligosaccharide repeat units comprise three to six sugar residues and are responsible for 0-antigen specificity (14). In S. enterica groups B, D, and A, the 0-antigen basic repeat units comprise four sugars, of which three form a backbone (mannosyl-rhamnosyl-galactose) common to the three groups. The fourth side chain sugar is a dideoxyhexose: abequose in group B, tyvelose in group D, and paratose in group A.The genes essential for the synthesis and assembly of the 0 antigen in S. enterica are located in the rfb gene cluster (9). In some strains, the basic structure is modified later by the addition of 0-acetyl or glucose residues, but this is not important for our study, as the genes do not map the rib locus. The three dideoxyhexose pathways diverge at the last step, with the only differences being the presence of CDPabequose synthase in group B but CDP-paratose synthase in groups A and D and an additional enzyme, CDP-paratose-2-epimerase, which converts CDP-paratose to CDP-tyvelose, Region A, which comprises the ends of the cluster from positions 0 to 11.7 and 16.5 to 22.8, is almost identical in the two strains and includes the rhamnose and mannose pathways and part of the common dideoxyhexose pathway (Fig. 1).In regions B, C, and D (from positions 11.7 to 16.5), there is only limited similarity (Fig. 1). Region B includes rfbS or ribJ in strains Ty2 and LT2, respectively. The nucleotide sequences of these genes have been determined (18,20), and comparison of the sequence data suggests that the two genes have a common ancestor but diverged a very long time ago (18). Region C is present only in strain Ty2 and comprises the ribE gene. In region D (from po...

Studies of the biosynthesis of 3,6-dideoxyhexoses: molecular cloning and characterization of the asc (ascarylose) region from Yersinia pseudotuberculosis serogroup VA

“…As shown in Fig. 6, the 3,6-dideoxyhexose biosynthetic genes were found to be clustered and relatively conserved throughout all four serogroups (20). It should be noted that many of these ORFs had been identified: rfF for glucose-i-phosphate cytidylyltransferase (Ep), rJbG for CDP-D-glucose 4,6-dehydratase (EOd), rJbJ for abequose synthase, rfbS for paratose synthase, and rflE for (Fig.…”

Application of PCR-based serogrouping of selected Salmonella serotypes in Malaysia

“…This rfb gene cluster that encodes many enzymes for O antigen biosynthesis and assembly is highly polymorphic and has been targeted as a molecular marker for detection of Salmonella serotypes. The rfb gene cluster of the more common Salmonella serogroups have been studied extensively at the molecular level to date [4,6,[11][12][13][14].…”

Cloning and structure of group C1 O antigen (rfb gene cluster) from Salmonella enterica serovar montevideo

“…However, the mannose genes of the cps gene cluster of strain LT2 have a G + C content of 61 % (Stevenson et al, 1991), and thus the rfblv region of M40, which hybridized at high stringency with pPR685, must also be of high G + C content. For the reasons given earlier for groups B (Jiang et al, 1991), D (Verma & Reeves, 1989;Liu et al, 1991), C2 (Brown et al, 1991) and El (Wang et al, 1992), one can argue that the evolution of most of the group C1 rfb region occurred within a low G + C content species prior to transfer to S. enterica, but the rfbK gene at least appears to have been derived from the Salmonella cps cluster.…”

“…typhimurium (strain LT2) (Brahmbhatt et al, 1988;Wyk & Reeves, 1989;Jiang et al, 1991), typhi and paratyphi (Verma et al, 1988;Verma & Reeves, 1989;Liu et (Wang et al, 1992), representative of groups B, D, A and El respectively. The genes for the rhamnose and mannose biosynthesis pathways and for the galactose transferase are very similar in all four strains.…”