Investigation of a Bacteroides fragilis homologue of eukaryotic ubiquitin and the associated role of outer membrane vesicles

• Main Author: O'Connor, Danny Joseph
• Published: Queen's University Belfast 2013
• Subjects: 616.079
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602717

The Gram negative obligate anaerobe Bacteroides fragilis has a dichotomous existence as a commensal bacterium and an opportunistic pathogen. B. fragilis is a normal resident of the G.I. tract and is thought to aid immune system development. Analysis of the whole genome sequences of B.fragilis NCTC9343 and 638R led to the discovery of the ubb gene, the gene product BfUbb, was detected in outer membrane vesicle (OMV) associated culture supernatant of both NCTC9343 and 638R. BfUbb shares 63% homology with human ubiquitin. Reactivity against human ubiquitin was noted in serum raised against recombinant BfUbb whilst human serum samples from patients with autoimmune disease demonstrated a range of reactivity against rBfUbb, the native BfUbb protein and eukaryotic ubiquitin. Four Taqman qPCR assays with specific gene targets were used to analyse a range of clinical samples. Two of the gene targets were; the bjt gene, the product of which is the B. fragils enterotoxin and the ubb gene. Analysis of a limited number of fresh colonic biopsies found an association between the presence of the ubb and bft genes in adherent B.fjragilis populations of inflammatory bowel disease (IBD) patients when compared with healthy controls. Immunofluorescence microscopy analysis of separate colonic biopsy sections suggested the presence of OMV producing adherent B. fragilis populations in samples from patients with IBD. OMVs have been shown to deliver immunomodulatory NCTC9343 polysaccharide A to dendritic cells, implying a commensal function. The current study highlights an association between OMVs and putative virulence factors involved in fibrinogen binding and degradation suggesting dual commensal and pathogenic functions. OMVs are also. thought to play a role in BfUbb secretion. The presence of significant amounts of this bacterial homologue of human ubiquitin could interfere with host ubiquitination and may have profound implications in relation to IBD and autoimmune disease.