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Appl. Environ. Microbiol. doi:10.1128/AEM.02806-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Bacteroides sp. D8: First Cholesterol-Reducing Bacterium Isolated from Human Feces

Unité d'Ecologie et Physiologie du Système Digestif, INRA, Domaine de Vilvert, 78352 Jouy en Josas Cedex, France; Laboratoire de Génie des Procédés et Technologies Alimentaires, INRA, 369 Rue Jules Guesde, F-59651 Villeneuve d'Ascq, France

^* To whom correspondence should be addressed. Email: philippe.gerard{at}jouy.inra.fr.

	Abstract

The microbial community in the human colon contains cholesterol-to-coprostanol reducing bacteria but the species responsible for this conversion are still unknown. We describe here the first isolation and characterization of a cholesterol-reducing bacterium of human intestinal origin. Strain D8 was isolated from a 10^-8 dilution of a fresh stool sample provided by a senior male volunteer with a high capacity to reduce luminal cholesterol to coprostanol. Cholesterol-to-coprostanol conversion by strain D8 started on the third day while cells were in stationary phase, and was almost complete after seven days. Intermediate products (4-cholesten-3-one and coprostanone) were occasionally observed, suggesting an indirect pathway for cholesterol-to-coprostanol conversion. Resting-cell assays showed that strain D8 could reduce 1.5 µmoles of cholesterol/mg bacterial protein/h. Strain D8 was a Gram-negative, non-spore forming rod-shaped organism identified as a Bacteroides closely related to B. vulgatus, based on its morphological and biochemical characteristics. The 16S rRNA gene sequence of strain D8 was most similar (>99.5%) to that of two isolates of the recently described Bacteroides dorei species. Phylogenetic tree construction confirmed that Bacteroides sp. D8 clustered within an independent clade, together with these B. dorei strains. Nevertheless, no cholesterol-reducing activity could be detected in cultures of B. dorei type strain. Based on Bacteroides group-specific PCR-temporal temperature gradient gel electrophoresis, there was no correlation between the presence of a band co-migrating with that of Bacteroides sp. D8 and cholesterol conversion in eleven human fecal samples, indicating that this species is unlikely to be mainly responsible for cholesterol conversion among human population.