Bacteroides xylanisolvens sp nov., a xylan-degrading bacterium isolated from human faeces

During the course of a study on the xylan-degrading community from the human gut, six xylanolytic, Gram-negative, anaerobic rods were isolated from faecal samples. 16S rRNA gene sequence analysis showed that the isolates were closely related to each other (>= 99 % sequence similarity) and that they belonged to the genus Bacteroides. On the basis of 16S rRNA gene sequence similarity, representative strain XB1A(T) was most closely related to the type strains of Bacteroides ovatus (97.5 %), B. finegoldii (96.5 %) and B. thetaiotaomicron (95.5 %). DNA-DNA hybridization results revealed that strain XB1A(T) was distinct from its closest relative, B. ovatus. The DNA G+C content of strain XB1A(T) (42.8 mol%) and major fatty acid composition (anteiso-C-15:0, 33.8%) further supported its affiliation to the genus Bacteroides. The novel isolates degraded different types of xylan, and were also able to grow on a variety of carbohydrates. Unlike most other Bacteroides species isolated from the human gut, these isolates were not able to degrade starch. Other biochemical tests further demonstrated that strain XB1A(T) could be differentiated from the closest related Bacteroides species. Xylan and sugars were converted by strain XB1A(T) mainly into acetate, propionate and succinate. Based on physiological, phenotypic and phylogenetic data, the six novel strains are considered to represent a novel species of the genus Bacteroides, for which the name Bacteroides xylanisolvens sp. nov. is proposed. The type strain is XB1A(T) (=DSM 18836 (T) =CCUG 53782 (T)).