Function and regulation of the polysaccharide utilization locus, don, in the gut symbiont bacteroides fragilis
Bacteroides fragilis is the most common anaerobe isolated from clinical infections and in this report we demonstrate a novel feature of the species that is critical to their success as an opportunistic pathogen. Among the Bacteroides spp. in the gut, B. fragilis has a unique ability to efficiently harvest complex N-linked glycans from the glycoproteins common to serum and serous fluid. This activity is mediated by a Sus-like outer membrane protein complex designated as Don. Using the abundant serum glycoprotein transferrin as a model it was shown that B. fragilis alone can rapidly and efficiently deglycosylate this protein in vitro and that transferrin glycans can provide the sole source of carbon and energy for growth in defined media. We then showed that transferrin deglycosylation occurs in vivo when B. fragilis is propagated in the rat tissue cage model of extraintestinal growth and that this ability provides a competitive advantage in vivo over strains lacking the don locus. Thus, Don functionally is an extraintestinal growth factor that may contribute to B. fragilis opportunistic infection. The regulation of don expression is controlled by two independent pathways. The first one was shown to be a typical ECF sigma/anti-sigma factor switch, commonly found in Sus-like Polysaccharide Utilization Loci (PULs), which responds to the presence of specific substrate. In the ECF sigma factor deletion mutant, [delta]donA, expression of the don PUL was completely abolished in the presence of substrate glycans, while the cognate anti-sigma deletion strain, [delta]donB, expressed the don genes even in the absence of substrate glycans. The donA overexpressing strain highly expressed the don PUL regardless of the substrate glycan presence. The second regulatory pathway is involved with a cis-encoded antisense sRNA which is associated within the don locus, DonS. DonS was shown to negatively regulate don expression. In contrast, expression of the don genes was induced two- to six-fold in the donS silencing mutant and highly repressed in the donS overexpressing strain. Notably, this sRNA controlled regulatory pathway is not commonly found associated with B. fragilis PULs. Only 14 of more than 50 PULs in B. fragilis possess DonS-like sRNAs, but at the present time their roles in commensal colonization and opportunistic infections is not understood.
Cao, Yanlu. (January 2014). Function and regulation of the polysaccharide utilization locus, don, in the gut symbiont bacteroides fragilis (Doctoral Dissertation, East Carolina University). Retrieved from the Scholarship. (http://hdl.handle.net/10342/4658.)
Cao, Yanlu. Function and regulation of the polysaccharide utilization locus, don, in the gut symbiont bacteroides fragilis. Doctoral Dissertation. East Carolina University, January 2014. The Scholarship. http://hdl.handle.net/10342/4658. August 22, 2019.
Cao, Yanlu, “Function and regulation of the polysaccharide utilization locus, don, in the gut symbiont bacteroides fragilis” (Doctoral Dissertation., East Carolina University, January 2014).
Cao, Yanlu. Function and regulation of the polysaccharide utilization locus, don, in the gut symbiont bacteroides fragilis [Doctoral Dissertation]. Greenville, NC: East Carolina University; January 2014.
East Carolina University