Identification and sequence of rfbS and rfbE, which determine antigenic specificity of group A and group D salmonellae

Abstract

Salmonella group A, group B, and group D strains have paratose, abequose, and tyvelose, respectively, as the immunodominant sugar in their 0 antigens, which are otherwise identical; only the final steps differ in the biosynthetic pathways of these sugars. The gene rjbJ from a group B strain, encoding abequose synthase, the final and only unique step in the biosynthesis of CDP-abequose, has been cloned and sequenced (P. Wyk and P. Reeves, J. Bacteriol. 171:5687-5693, 1989 The evolutionary origin of these genes is discussed.We are studying the genetics of a major polymorphism in bacteria, and in the accompanying paper (13), we described and gave the sequence of the rfbJ gene of Salmonella strain LT2 (serovar typhimurium), which encodes the enzyme abequose synthase and determines the 04 epitope characteristic of the 0 antigen of serogroup B strains of salmonellae. In this paper we describe the identification and sequencing of the genes which determine the distinguishing immunodominant sugars for the related 0 antigens of serogroups A and D.The 0 antigen, a polysaccharide on the cell surface, is in groups A, B, and D a polymer with a repeat unit of four sugars, of which three form a backbone (mannosyl-rhamnosyl-galactose) common to all three groups, while the fourth sugar is a dideoxyhexose linked (al,3) to the mannose residue. The dideoxyhexose is paratose in group A, abequose in group B, and tyvelose in group D. The biosynthetic pathways for these three sugars diverge only at the last steps (Fig. 1). The genes encoding paratose synthase and CDPtyvelose-2-epimerase have not been named previously, and we propose the names rflS and rJbE, respectively. See the accompanying study (13) for a more detailed introduction.The genes for the biosynthetic pathways of the dideoxyhexoses are in the rfb gene cluster of the respective strains, and we have shown that there is a region of low homology in the general area of the genes for the latter part of the pathway (12, 13). In the accompanying study (13) fied in a group D strain and is shown to be present also in a group A strain but in a mutant form. The inferred amino acid sequences for RfbS and RfbE show that both proteins have homology with well-documented dehydrogenases. MATERIALS AND METHODSStrains used as sources of DNA or for cloning are described in Table 1. All plasmids used contained DNA from the rib regions of Ty2 (Ty2la was used as the source) or IMVS1316, cloned into pUC9 or pUC18. The extent of the cloned DNA has been indicated in the summary diagram (see Fig. 6), as have the vector name and the orientation of the insert.The serovars and sources of group A, B, and D strains used for probing with ribE DNA were as given below (see Acknowledgments for full names of sources). Group A, 5 paratyphi A were from ICPMR and 3 paratyphi A were from MDUM; and one nitra, one kiel, and one paratyphi A var. durazzo were from Le Minor. Group B, 2 typhimurium, one stanley, one derby, and one budapest were from IMVS; one agona, one heidelberg, one bredeney, one hessarek, one derby,...

Molecular Epidemiology of Nontyphoidal Salmonella in Poultry and Poultry Products in India: Implications for Human Health

“…Allele specific PCR has been widely used to differentiate the group D Salmonella from other groups and non Salmonella [17,35,36]. By allele specific PCR, four isolates were identified as S. Enteritidis and one isolate (S585) could not be identified possibly due to the loss or absence of the specific sites for primer binding in the chromosomal DNA.…”

A Novel NDP-6-deoxyhexosyl-4-ulose Reductase in the Pathway for the Synthesis of Thymidine Diphosphate-d-fucose

“…The amino acid sequence deduced from the fcd gene showed an identity of Ͻ10% with previously reported proteins in a homology search using the program FASTA. However, a BLAST search showed that the amino acid sequence of the fcd gene product shared limited homology with that of CDP-abequose synthase of Salmonella enterica LT2 (39). CDP-Abequose synthase catalyzes a similar reaction, in which the keto group on carbon 4 of a hexosyl group is attacked.…”

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

“…The tyv gene encodes CDP-tyvelose epimerase, which further converts CDP-paratose to CDPtyvelose. However, tyv gene of group A does not produce active CDP-tyvelose epimerase due to the 1-bp deletion which causes the frameshift mutation and converts the fourth codon to an amber stop codon [15]. Salmonella groups B and C2 were found to have rfbJ genes which encode abequose synthase, converting CDP-4-keto-3,6-dideoxyglucose to CDPabequose.…”