Effect of arabinogalactan on the gut microbiome: A randomized, double-blind, placebo-controlled, crossover trial in healthy adults.

OBJECTIVE: Promising evidence suggests beneficial health effects of arabinogalactan, but little is known about the effect of this non-digestible carbohydrate on the gut microbiota, a crucial mediator of human health. The objective of this study was to investigate the effect of an arabinogalactan product (ResistAid) on the fecal microbiome and short-chain fatty acids and gastrointestinal tolerance in healthy adults in a randomized, double-blind, crossover trial. METHODS: Thirty adults were randomly assigned to consume 15 g/d maltodextrin (control) or ResistAid for 6 wk. RESULTS: At week 6, compared to placebo, ResistAid supplementation led to a significant decrease in the ratio of fecal Firmicutes to Bacteroidetes, driven by an increase in Bacteroidetes and a decrease in Firmicutes. Moreover, the relative abundance of Bifidobacterium tended to increase with ResistAid supplementation. Additionally, ResistAid significantly decreased the α-diversity of the fecal microbiome. Predicted functional abundances based on 16S rRNA sequences showed that ResistAid supplementation increased the gene abundance of the gut microbiome for α-l-rhamnosidase, ß-fructosidase, and levanase, as well as tricarboxylic acid and vitamin B6 biosynthesis pathways. Fecal isovaleric, valeric, and hexanoic acids were significantly lower after ResistAid consumption. There were no statistically significant changes in bowel habit, stool consistency, gastrointestinal tolerance symptoms, chemistry profile, metabolic panel, or vitals, suggesting that consumption of 15 g daily ResistAid over 6 wk is safe. CONCLUSION: These results demonstrate that the gut microbiome composition and predicted functions can be modulated by ResistAid consumption, perhaps suggesting a mechanistic explanation on its reported benefits in metabolic parameters and the immune system.

Evolutionary transition in symbiotic syndromes enabled diversification of phytophagous insects on an imbalanced diet.

Evolutionary adaptations for the exploitation of nutritionally challenging or toxic host plants represent a major force driving the diversification of phytophagous insects. Although symbiotic bacteria are known to have essential nutritional roles for insects, examples of radiations into novel ecological niches following the acquisition of specific symbionts remain scarce. Here we characterized the microbiota across bugs of the family Pyrrhocoridae and investigated whether the acquisition of vitamin-supplementing symbionts enabled the hosts to diversify into the nutritionally imbalanced and chemically well-defended seeds of Malvales plants as a food source. Our results indicate that vitamin-provisioning Actinobacteria (Coriobacterium and Gordonibacter), as well as Firmicutes (Clostridium) and Proteobacteria (Klebsiella) are widespread across Pyrrhocoridae, but absent from the sister family Largidae and other outgroup taxa. Despite the consistent association with a specific microbiota, the Pyrrhocoridae phylogeny is neither congruent with a dendrogram based on the hosts' microbial community profiles nor phylogenies of individual symbiont strains, indicating frequent horizontal exchange of symbiotic partners. Phylogenetic dating analyses based on the fossil record reveal an origin of the Pyrrhocoridae core microbiota in the late Cretaceous (81.2-86.5 million years ago), following the transition from crypt-associated beta-proteobacterial symbionts to an anaerobic community localized in the M3 region of the midgut. The change in symbiotic syndromes (that is, symbiont identity and localization) and the acquisition of the pyrrhocorid core microbiota followed the evolution of their preferred host plants (Malvales), suggesting that the symbionts facilitated their hosts' adaptation to this imbalanced nutritional resource and enabled the subsequent diversification in a competition-poor ecological niche.