Patrick S, Houston S, Thacker Z, Blakely GW. Mutational analysis of genes implicated in LPS and capsular polysaccharide biosynthesis in the opportunistic pathogen Bacteroides fragilis.
MICROBIOLOGY-SGM 2009;
155:1039-1049. [PMID:
19332806 DOI:
10.1099/mic.0.025361-0]
[Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The obligate anaerobe Bacteroides fragilis is a normal resident of the human gastrointestinal tract. The clinically derived B. fragilis strain NCTC 9343 produces an extensive array of extracellular polysaccharides (EPS), including antigenically distinct large, small and micro- capsules. The genome of NCTC 9343 encodes multiple gene clusters potentially involved in the biosynthesis of EPS, eight of which are implicated in production of the antigenically variable micro-capsule. We have developed a rapid and robust method for generating marked and markerless deletions, together with efficient electroporation using unmodified plasmid DNA to enable complementation of mutations. We show that deletion of a putative wzz homologue prevents production of high-molecular-mass polysaccharides (HMMPS), which form the micro-capsule. This observation suggests that micro-capsule HMMPS constitute the distal component of LPS in B. fragilis. The long chain length of this polysaccharide is strikingly different from classical enteric O-antigen, which consists of short-chain polysaccharides. We also demonstrate that deletion of a putative wbaP homologue prevents expression of the phase-variable large capsule and that expression can be restored by complementation. This suggests that synthesis of the large capsule is mechanistically equivalent to production of Escherichia coli group 1 and 4 capsules.
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