Molecular Analysis of the rfb Gene Cluster of a Group D2 Salmonella enterica Strain: Evidence for Its Origin from an Insertion Sequence-Mediated Recombination Event between Group E and Dl Strains

Authors

Shi-Hua Xiang, University of Nebraska-LincolnFollow
Matthew Hobbs, University of Sydney, Australia
Peter R. Reeves, University of Sydney, AustraliaFollow

Document Type

Article

Date of this Version

7-1994

Comments

Published in JOURNAL OF BACTERIOLOGY, JUly 1994, p. 4357-4365 Vol. 176, No. 14 0021-9193/94/$04.00+0

Used by permission

Abstract

The Salmonella enterica O antigen is a highly variable surface polysaccharide composed of a repeated oligosaccharide (the O unit). The O unit produced by serogroup D2 has structural features in common with those of groups Dl and El, and hybridization studies had previously suggested that the D2 rfb gene cluster responsible for O-unit biosynthesis is indeed a hybrid of the two. In this study, the rfb gene cluster was cloned from a group D2 strain of S. enterica sv. Strasbourg. Mapping, hybridization, and DNA sequencing showed that the organization of the D2 rfb genes is similar to that of group Dl, with the α-mannosyl transferase gene rfbU replaced by rfbO, the E1-specific β-mannosyl transferase gene. The El-specific polymerase gene (rfc) has also been acquired. Interestingly, the Dl-like and El-like rfb regions are separated by an additional sequence closely related to an element ( Hinc repeat [H-rpt]) associated with the Rhs loci of Escherichia coli. The H-rpt resembles an insertion sequence and possibly mediated the intraspecific recombination events which produced the group D2 rfb gene organization.