Glycan Utilization Strategy of the Butyrate Producing Gut Symbiont Roseburia intestinalis
Abstract
The human gut microbiota’s (HGM’s) interplay with the host and diet exerts a profound impact on our health. Dietary fibers, which are fermented to short chain fatty acids (SCFAs), are key in shaping the composition and the metabolic output of the HGM. The SCFA butyrate, produced mainly by Clostridium XIVa Firmicutes modulates host immune homeostasis and confers protection from inflammatory disorders and colorectal cancer. Despite this vital role on human health, the mechanisms underpinning the utilization of dietary fibers by butyrate producers are largely unexplored. This thesis aims at bringing insight into this facet using the abundant and prevalent butyrogenic bacterium Roseburia intestinalis as a model system . The major dietary fiber xylan is shown to be an excellent substrate for R. intestinalis in this work. Transcriptomic analysis identified the molecular apparatus that confers growth on xylan, including a key cell-attached modular xylanase of glycoside hydrolase family 10 (GH10). This enzyme harbor a new low affinity xylan binding module, which showed an atypical architecture, featuring an open and shallow binding site with a few polar contacts to a single xylosyl unit. Investigation of transport and intracellular hydrolysis outlined a model for xylan breakdown to monosaccharides. An ATP-binding cassette (ABC) transporter with preference for 4-5 xylosyl units creates a competitive window that enables R. intestinalis to co-grow with key primary xylan degraders from the Bacteroides genus, which possess an uptake preference for larger ligands. R. intestinalis uses a similar approach, as described above, to capture, degrade and transport complex dietary β-mannans. Capture and depolymerisation of mannan is initiated by a modular GH26 mannanase and the mannan-oligosaccharides are subsequently imported into the cell for further hydrolysis using an ABC uptake system. An in vivo experiment in mice colonized by a mock community of human commensals showed that β-mannan boosts commensal mannan degraders, including R. intestinalis . Altogether, this project highlights the differentiation of capture and transport preferences of primary glycan degraders using xylan as a model. It provides a potential strategy for promotion of key members of a healthy HGM, by designing prebiotics that selectively target specific health promoting taxonomic groups.
Info
Thesis PhD, 2019
UN SDG Classification
DK Main Research Area
Science/Technology
