Bacteroides thetaiotaomicronmetabolic activity decreases with polysaccharide molecular weight

Abstract

AbstractThe human colon hosts hundreds of commensal bacterial species, many of which ferment complex dietary carbohydrates. To transform these fibers into metabolically-accessible compounds, microbes often express series of dedicated enzymes homologous to the starch utilization system (sus) encoded in polysaccharide utilization loci (PULs). The genome ofBacteroides thetaiotaomicron (Bt),a common member of the human gut microbiota, encodes nearly 100 PULs, conferring a strong metabolic versatility. While the structures and functions of individual enzymes within the PULs have been investigated, little is known about how polysaccharide complexity impacts the function of sus-like systems. We here show that the activity of sus-like systems depends on polysaccharide size, ultimately impacting bacterial growth. We demonstrate the effect of size-dependent metabolism in the context of dextran metabolism driven by the specific utilization system PUL48. We find that as molecular weight of dextran increases,Btgrowth rate decreases and lag time increases. At the enzymatic level, the dextranase BT3087 is the main glycosylhydrolase for dextran utilization and that BT3087 and BT3088 contribute toBtdextran metabolism in a size-dependent manner. Finally, we show that the polysaccharide size-dependent metabolism ofBtimpacts its metabolic output in a way that modulates the composition of a producer-consumer community it forms withBacteroides fragilis. Altogether, our results expose an overlooked aspect ofBtmetabolism which can impact the composition and diversity of microbiota.