Trans locus inhibitors limit concomitant polysaccharide synthesis in the human gut symbiont Bacteroides fragilis

Abstract

Bacteroides is an abundant genus of bacteria of the human intestinal microbiota. Bacteroides species synthesize a large number of capsular polysaccharides (PS), a biological property not shared with closely related oral species, suggesting importance for intestinal survival. Bacteroides fragilis, for example, synthesizes eight capsular polysaccharides per strain, each of which phase varies via inversion of the promoters located upstream of seven of the eight polysaccharide biosynthesis operons. In a single cell, many of these polysaccharide loci promoters can be simultaneously oriented on for transcription of the downstream biosynthesis operons. Here, we demonstrate that despite the promoter orientations, concomitant transcription of multiple polysaccharide loci within a cell is inhibited. The proteins encoded by the second gene of each of these eight loci, collectively designated the UpxZ proteins, inhibit the synthesis of heterologous polysaccharides. These unique proteins interfere with the ability of UpxY proteins encoded by other polysaccharide loci to function in transcriptional antitermination of their respective operon. The eight UpxZs have different inhibitory spectra, thus establishing a hierarchical regulatory network for polysaccharide synthesis. Limitation of concurrent polysaccharide synthesis strongly suggests that these bacteria evolved this property as an evasiontype mechanism to avoid killing by polysaccharide-targeting factors in the ecosystem.

Characterizing the Interactions between a Naturally Primed Immunoglobulin A and Its Conserved Bacteroides thetaiotaomicron Species-specific Epitope in Gnotobiotic Mice

“…These patterns of ELISA reactivity support a model in which the expression of the 260.8 epitope is relatively stable across isolates in a given sample, whereas expression of the 225.4 epitope is under phase variable control. Consistent with this model, homologs of UpxY and UpxZ, which help mediate phase variation of capsular polysaccharides in B. fragilis (42), are present in the 225.4 locus but not in the 260.8 locus.…”

Two Multidrug-Resistant Clinical Isolates of Bacteroides fragilis Carry a Novel Metronidazole Resistance nim Gene ( nimJ )

“…The expression vector pMCL140, noted for its robust transcription levels of inserted genes (35), was a kind gift from Laurie Comstock (Channing Laboratory, Harvard Medical School). SmaI (New England BioLabs, Ipswich, MA) was used to linearize pMCL140.…”

Longitudinal Analysis of the Prevalence, Maintenance, and IgA Response to Species of the Order Bacteroidales in the Human Gut

“…In nearly all of the B. fragilis bacteria of this ecosystem, the PSG locus promoter was consistently oriented on. Our in vitro studies have shown that the UpgZ protein, encoded by the PSG region, has a very wide spectrum of inhibition, preventing the transcription of all PS biosynthesis loci except PSG and PSH (4). Due to the fact that nearly all of the B. fragilis isolates from subject 14 had the PSH biosynthesis locus promoter oriented off at all time points, we predict that nearly all of the B. fragilis bacteria of subject 14 consistently and exclusively expressed PSG over the year of study.…”

“…The first, collectively designated the UpxY proteins, are transcriptional antitermination factors necessary to prevent premature transcriptional termination in the 5Ј untranslated region of each operon (3). The proteins encoded by the second gene of each locus are termed the UpxZ proteins and function to inhibit the transcriptional antitermination property of subsets of heterol-ogous UpxY proteins (4). The UpxZ proteins have differential inhibitory spectra, establishing a hierarchical mode of regulation.…”