Genetic diversity of <FONT FACE=Symbol>b</font>-glucuronidase activity among 14 strains of the dominant human gut anaerobe Ruminococcus gnavus

Abstract

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

Distribution of β-glucosidase and β-glucuronidase activity and of β-glucuronidase gene gus in human colonic bacteria

“…Bacteroides ovatus DCNC 11 exhibited by far the highest β‐glucosidase activity of all strains tested, whereas we could not detect this activity in B. ovatus V975. However, the different strains used might behave differently, analogous to the differences McBain & Macfarlane (1998) have found for Bifidobacterium and Beaud et al (2006) for R. gnavus strains. Bifidobacterium breve DSM 20213 T (NCFB 2257) displayed only detectable β‐glucosidase activity in our study, whereas McBain & Macfarlane (1998) found both enzyme activities with intact cells; however, β‐glucuronidase activity was lower than β‐glucosidase activity.…”

“…Only one strain, B. ovatus V975, exhibited a faint band by degenerate PCR while it did not show detectable β‐glucuronidase activity; however, the cloned fragment showed only low similarity to the translated gus gene and is therefore unlikely to code of a homologous enzyme. Beaud et al (2006) screened for the presence of the gus gene in a range of R. gnavus strains by degenerate PCR and Southern hybridization, and found strains harbouring enzyme activity that were negative in the molecular screen and vice versa. Therefore, more work is needed to resolve whether this gene is indeed responsible for the enzyme activities measured here.…”

Ruminococcus gnavus: friend or foe for human health

“…Some R. gnavus strains have β-glucuronidase (GUS) activity when grown in rich media (Beaud et al 2006 ). GUS belongs to GH families 1, 2, 3, 30, 79, 154, and 169 ( www.cazy.org ).…”