Cloning and characterization of arabinoxylan arabinofuranofydrolases-D3 (AXHd3) from Bifidobacterium adolescentis DSM20083

Arabinoxylan arabinofuranohydrolase-D3 (AXHd3) from Bifidobacterium adolescentis releases only C3-linked arabinose residues from double-substituted xylose residues. A genomic library of B. adolescentis DSM20083 was screened for the presence of the axhD3 gene. Two plasmids were identified containing part of the axhD3 gene. The nucleotide sequences were combined and three open reading frames (ORFs) were found. The first ORF showed high homology with xylanases belonging to family 8 of the glycoside hydrolases and this gene was designated xylA. The second ORF was the axhD3 gene belonging to glycoside hydrolase family 43. The third (partial) ORF coded for a putative carboxylesterase. The axhD3 gene was cloned and expressed in Escherichia coli. Several substrates were employed in the biochemical characterization of recombinant AXHd3. The enzyme showed the highest activity toward wheat arabinoxylan oligosaccharides. In addition, -xylanase from Trichoderma sp. was able to degrade soluble wheat arabinoxylan polymer to a higher extent, after pretreatment with recombinant AXHd3. Arabinoxylan oligosaccharides incubated with a combination of recombinant AXHd3 and an -l-arabinofuranosidase from Aspergillus niger did not result in a higher maximal release of arabinose than incubation with these enzymes separately

Preparative-scale isolation and characterisation of 61-α-D-galactosyl-(1→4)-β-D-mannobiose and 62-α-D-galactosyl-(1→4)-β-D-mannobiose

International audienc

In vitro fermentation of oat and barley derived beta-glucans by human faecal microbiota

Fermentation of beta-glucan fractions from barley [average molecular mass (MM), of 243, 172, and 137 kDa] and oats (average MM of 230 and 150 kDa) by the human faecal microbiota was investigated. Fractions were supplemented to pH-controlled anaerobic batch culture fermenters inoculated with human faecal samples from three donors, in triplicate, for each substrate. Microbiota changes were monitored by fluorescent in situ hybridization; groups enumerated were: Bifidobacterium genus, Bacteroides and Prevotella group, Clostridium histolyticum subgroup, Ruminococcus-Eubacterium-Clostridium (REC) cluster, Lactobacillus-Enterococcus group, Atopobium cluster, and clostridial cluster IX. Short-chain fatty acids and lactic acid were measured by HPLC. The C. histolyticum subgroup increased significantly in all vessels and clostridial cluster IX maintained high populations with all fractions. The Bacteroides-Prevotella group increased with all but the 243-kDa barley and 230-kDa oat substrates. In general beta-glucans displayed no apparent prebiotic potential. The SCFA profile (51 : 32 : 17; acetate : propionate : butyrate) was considered propionate-rich. In a further study a beta-glucan oligosaccharide fraction was produced with a degree of polymerization of 3-4. This fraction was supplemented to small-scale faecal batch cultures and gave significant increases in the Lactobacillus-Enterococcus group; however, the prebiotic potential of this fraction was marginal compared with that of inulin