Bacteroides sp. Strain D8, the First Cholesterol-Reducing Bacterium Isolated from Human Feces

Abstract

The microbial community in the human colon contains bacteria that reduce cholesterol to coprostanol, 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 7 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 mol of cholesterol/mg bacterial protein/h. Strain D8 was a gram-negative, non-spore-forming, rod-shaped organism identified as a member of the genus Bacteroides closely related to Bacteroides vulgatus, based on its morphological and biochemical characteristics. The 16S rRNA gene sequence of strain D8 was most similar (>99.5%) to those of two isolates of the recently described species Bacteroides dorei. Phylogenetic tree construction confirmed that Bacteroides sp. strain D8 clustered within an independent clade together with these B. dorei strains. Nevertheless, no cholesterol-reducing activity could be detected in cultures of the 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 comigrating with the band of Bacteroides sp. strain D8 and cholesterol conversion in 11 human fecal samples, indicating that this strain is unlikely to be mainly responsible for cholesterol conversion in the human population.

Preliminary Safety Evaluation of a New Bacteroides xylanisolvens Isolate

“…Other genera, like the genus Bacteroides, which is the second most frequently represented genus in the human intestine (exceeding Lactobacillus and Bifidobacterium by up to four orders of magnitude), may embody great potential for the isolation and development of new probiotic strains. Thus, two recent studies presented specific Bacteroides strains isolated from human feces for increasing the production of mucosal IgA (54) and removing cholesterol from enterohepatic cycling (13). However, the unknown or even ambiguous safety status of some Bacteroides species may have prevented the probiotic community from investigating their potential.…”

Current and Future Applications of Probiotics

“…For instance Oxalobacter formigenes may have a potential role to play in the risk reduction for kidney stone formation [162]. A Bacteroides strain, able to reduce cholesterol, isolated from the gut microbiota of a subject with a high ability to reduce cholesterol to coprostanol has also been reported [163]. Such microorganisms may constitute the basis for future targeted probiotic developments.…”

Les relations entre microbiote intestinal et lipides

“…Ce n'est qu'en 2007 qu'une souche bacté-rienne convertissant le cholestérol et issue d'un microbiote fécal humain a été isolée et caractérisée pour la première fois. Cette souche est étroitement apparentée à l'espèce Bacteroides dorei [22] dont la souche type est cependant incapable de convertir le cholestérol. Par ailleurs, une étude réalisée sur 17 patients a montré que le taux de coprostanol présent dans les selles était inversement corrélé avec le taux de cholestérol sanguin [23], ce qui suggère que ce méta-bolisme microbien intestinal du cholestérol pourrait limiter l'absorption du cholestérol, la cholestérolémie et donc le risque de maladies cardio-vasculaires.…”