Probiotics in human gut microbiota can degrade host glycosaminoglycans

Glycosaminoglycans (GAGs) (e.g. heparin, chondroitin sulfate, and hyaluronan) show various significant physiological functions as a major component of extracellular matrix in animals. Some bacteria target GAGs for adhesion and/or infection to host cells, although no probiotics have been known to degrade GAGs. Here, we show GAG degradation by probiotics from human gut microbiota and their adhesion to human intestinal cells through a GAG. GAG-degrading bacteria were isolated from human faeces and identified as Enterococcus faecium, and some typical probiotics such as Lactobacillus casei, Lactobacillus rhamnosus and Enterococcus faecalis were also found to degrade heparin. GAG-degrading lactobacilli and enterococci including the isolated E. faecium possessed a genetic cluster encoding GAG-degrading/metabolising enzymes in the bacterial genome. KduI and KduD enzymes encoded in the GAG cluster of L. rhamnosus functioned as 4-deoxy-l-threo-5-hexosulose-uronate ketol-isomerase and 2-keto-3-deoxy-d-gluconate dehydrogenase, respectively, both of which were crucial for GAG metabolism. GAG-degrading L. rhamnosus and E. faecium attached to human intestinal Caco-2 cells via heparin. Some species of Bacteroides, considered to be the next generation probiotics, degraded chondroitin sulfate C and hyaluronan, and genes coding for the Bacteroides GAG-degrading enzyme were frequently detected from human gut microbiota. This is the first report on GAG-degrading probiotics in human gut microbiota.