Metabolism of β-mannans by representative, understudied Bacillota species from the human colon

The macronutrients in our diets including non-starch polysaccharides such as β-mannans, found in plant cell walls, can impact on human gut health. There is however a paucity of data regarding the ability of gut bacteria, in particular those belonging to the Bacillota (previously Firmicutes) phylum, to depolymerise and ferment β-mannans. In this study, we tested a total of 12 strains, including nine Bacillota, for their ability to metabolise and cross-feed on β-mannans. Three of the six butyrate-producing Bacillota strains, namely Roseburia intestinalis L1-82, Roseburia faecis M72/1, and Coprococcus eutactus ART55/1, were able to metabolise carob galactomannan, konjac glucomannan, and softwood spruce acetylated galactoglucomannan, which corresponded with their carbohydrate active enzyme profiles, whilst Faecalibacterium prausnitzii S3L/3 only grew well on β-mannan endo-mannanase digests. To investigate competition and microbial cross-feeding on β-mannans, growth assays were conducted with co-cultures of up to six strains belonging to both the Bacillota phylum and a Bacteroidetes β-mannan utilising strain, Bacteroides ovatus V975. All strains in the mixes were able to co-exist, including the non-mannan degrading butyrate producers, with butyrate being formed as one of the major fermentation products. These studies suggest that β-mannans may offer a notable prebiotic approach to promoting butyrate-producing bacteria and gut health.