Abstract
The Bifibobacterium longum subsp. longum 35624™ strain (formerly named Bifidobacterium longum subsp. infantis) is a well described probiotic with clinical efficacy in Irritable Bowel Syndrome clinical trials and induces immunoregulatory effects in mice and in humans. This paper presents (a) the genome sequence of the organism allowing the assignment to its correct subspeciation longum; (b) a comparative genome assessment with other B. longum strains and (c) the molecular structure of the 35624 exopolysaccharide (EPS624). Comparative genome analysis of the 35624 strain with other B. longum strains determined that the sub-speciation of the strain is longum and revealed the presence of a 35624-specific gene cluster, predicted to encode the biosynthetic machinery for EPS624. Following isolation and acid treatment of the EPS, its chemical structure was determined using gas and liquid chromatography for sugar constituent and linkage analysis, electrospray and matrix assisted laser desorption ionization mass spectrometry for sequencing and NMR. The EPS consists of a branched hexasaccharide repeating unit containing two galactose and two glucose moieties, galacturonic acid and the unusual sugar 6-deoxy-L-talose. These data demonstrate that the B. longum 35624 strain has specific genetic features, one of which leads to the generation of a characteristic exopolysaccharide.
Highlights
The gut microbiome contributes to host health by multiple mechanisms, including digestion, competitive exclusion of pathogens, degradation of mucins, enhancement of epithelial cell differentiation and promotion of mucosa-associated lymphoid tissue proliferation [1, 2]
Classification as based on the phylogenetic supertree approach clearly shows that these three strains are positioned within the B. longum subsp. longum phylogenetic group, and represent bona fide members of the subspecies longum, their original miss-assignment being due to the sole use of 16S rRNAbased taxonomic classification [23]
Bifidobacteria comprise a significant proportion of the gut microbiota, in particular in infants, and many strains are used as probiotics
Summary
The gut microbiome contributes to host health by multiple mechanisms, including digestion, competitive exclusion of pathogens, degradation of mucins, enhancement of epithelial cell differentiation and promotion of mucosa-associated lymphoid tissue proliferation [1, 2]. Induction of T regulatory cells by B. longum 35624 strain (35624) in mice is associated with protection against colitis, arthritis, allergic responses and pathogen-induced inflammation [11,12,13,14,15]. Administration of this bacterium to humans increases Foxp3+ lymphocytes in peripheral blood, enhances IL-10 secretion ex vivo, and reduces the level of circulating proinflammatory biomarkers in a wide range of patient groups and healthy volunteers [16, 17]. A number of host mechanisms have been described, which contribute to the anti-inflammatory activity of this microbe, including TLR-2 and DC-SIGN recognition, and retinoic acid release by dendritic cells [16, 18]
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