Yeast-Derived β-1,3-Glucan Substrate Significantly Increased the Diversity of Methanogens During In vitro Fermentation of Porcine Colonic Digesta

The β-1,3-glucan from yeast has been extensively examined for its immuno-enhancing effects in animals. However, investigation on the relationship among β-glucan, gut microbiota and immune-modulating effects remains limited particularly in pigs. Considering the critical roles of gut methanogens in the microbial fermentation, energy metabolism and disease resistance, we investigated the phylogenetic diversity of methanogens from fermented cultures of porcine colonic digesta with (G) or without (N) yeast β-glucan based on sequences of the archaeal 16S rRNA gene. A total of 145 sequences in the G library were assigned into 8 operational taxonomic units (OTUs) with the majority of sequences (114/145) related to strains Methanobrevibacter millerae or Methanobrevibacter gottschalkii with high identities ranging from 97.9 to 98.6%, followed by 23 sequences to Methanobrevibacter ruminantium, 2 sequences to Methanobrevibacter smithii and one sequence to Methanobrevibacter wolinii. The 142 sequences in the N library were assigned to 2 OTUs with most sequences (127/142) related to strains M. millerae or M. gottschalkii with sequence identities ranging from 97.9 to 98.5%, and 15 sequences related to M. gottschalkii with 97.9% identity. Shannon diversity index showed that the G library exhibited significantly higher archaeal diversity (P<0.05) and Libshuff analysis indicated the differences in the community structure between the two libraries were significant (P<0.0001). In conclusion, the current study provides evidence that addition of yeast β-glucan significantly increased the diversity of methanogens in in vitro fermented porcine colonic digesta.