Arabinogalactan Utilization by subsp. NCC 2705 and ATCC 43185 in Monoculture and Coculture.

Arabinogalactan (AG) has been studied as a potential prebiotic in view of stimulating bifidobacteria presence in the gut microbiota. However, bifidobacteria prefer fermentation of oligosaccharides to that of polysaccharides. The contribution of other gut bacteria may allow better growth of bifidobacteria on AG. β-galactanases and β-galactosidases are the main enzymes for the degradation of AG. Additional enzymes such as α-L-arabinofuranosidase and β-L-arabinopyranosidase are required to remove the arabinose side chains. All of these predicted functions are encoded by the genomes of both subsp. NCC 2705 and ATCC 43185. However, neither strain was able to grow significantly on AG, with 25% ( subsp. NCC 2705) and 39% ( ATCC 43185) of AG degraded after 48-h fermentation, respectively. In this study, the β-galactanase, β-galactosidase, α-L-arabinofuranosidase, and β-L-arabinopyranosidase from both strains were investigated. The extracellular β-galactosidases of both subsp. NCC 2705 and ATCC 43185 were able to cleave the β-1,3; 1,4 and 1,6 linkages. However, the β-galactosidase activity of subsp. NCC 2705 was weaker for the β-1,4 linkage, compared with the β-1,3 and 1,6 linkages. The arabinose side chains of AG inhibited the cleavage of β-1,3 and 1,6 linkages by the endo-β-galactanase from both strains, and partially inhibited the cleavage of β-1,4 linkages by the endo-β-1,4 galactanase from ATCC 43185. The α-L-arabinofuranosidase and β-L-arabinopyranosidase from both strains were unable to cleave arabinose from AG under the conditions used. These results show limited breakdown of AG by these two strains in monoculture. When cocultured with ATCC 43185, subsp. NCC 2705 grew significantly better than in monoculture on AG after 6 h of fermentation ( < 0.05). The coculture showed 48% AG degradation after 48 h of fermentation, along with reduced pH. Furthermore, compared to monoculture of ATCC 43185, the concentration of succinate significantly increased from 0.01 ± 0.01 to 4.41 ± 0.61 mM, whereas propionate significantly decreased from 13.07 ± 0.37 to 9.75 ± 2.01 mM in the coculture ( < 0.05). These results suggest that the growth and metabolic activities of ATCC 43185 were restrained in the coculture, as the pH decreased due to the metabolism of subsp. NCC 2705.