How do gut microbes break down dietary fiber?

Trillions of commensal bacteria in our colon thrive on what we do not digest in our small intestine. Many have evolved multiple sophisticated machineries, termed polysaccharide utilization loci or PULs, for carbohydrate breakdown; each PUL may target a particular complex carbohydrate. Until now, studies have focused on the structural and functional characterization of individual PUL constituents. A recent work by Larsbrink et al. moves the scope from single-gene analysis to the entire PUL dissection.