Genetic diversity of beta -glucuronidase activity among 14 strains of the dominant human gut anaerobe Ruminococcus gnavus

Bacterial beta -glucuronidase activity in the gut increases the enterohepatic circulation of toxic compounds and plays a major role in the etiology of colon cancer. Previously, we had found that the gus gene, which codes for beta -glucuronidase in a dominant anaerobic species of the gut microbiota, Ruminococcus gnavus strain E1, is transcribed as part of an operon that includes three ORFs that code for beta -glucoside permeases of the phosphotransferase systems. This genetic organization had never been described. We have now compared beta -glucuronidase activity and the genetic environment of the gus gene in 14 strains of Ruminococcus gnavus. We found that five out of the seven glucuronidase-positive R. gnavus strains possessed another glucuronidase gene different from the gusA operon of R. gnavus E1. This dominant commensal intestinal species appears to have a high degree of genetic diversity in the genes that control beta -glucuronidase activity.