Functional Analysis of Seasonally‐Changing Gut Microbiotas in Hibernating Ground Squirrels

Host diet influences the gut microbiota in species that regularly consume food. We showed that winter fasting in hibernating ground squirrels increases relative abundance of bacterial taxa that can degrade host glycans (e.g., mucins) and reduces abundance of taxa that prefer plant glycans. Here we determined the functional significance of seasonally changing microbiotas by gavaging summer squirrels and aroused hibernators in early and late winter with 13 C‐inulin (25 mg/kg), a plant‐derived fiber resistant to digestion by mammalian enzymes. Subsequent measurement of δ 13 CO 2 in breath over 2‐4 h was used an index of bacterial degradation of 13 C‐inulin. Compared with summer, peak changes in δ 13 CO 2 in hibernators were delayed and/or reduced by 60‐90% after 1 month of hibernation (early winter) and nearly abolished after 4 months (late winter). Intraperitoneal injection of 13 C‐inulin in summer squirrels produced minimal changes in breath δ 13 CO 2 , confirming the bacterial nature of the δ 13 C signal. The results suggest that over the hibernation season, the gut microbiota loses the capacity to degrade a plant glycan, consistent with the shift away from taxa that prefer dietary substrates. Measurement of δ 13 CO 2 in breath is a useful tool to determine functional capacities of gut microbiotas in species that undergo marked changes in food intake. Further insight will be obtained from {1H‐ 13 C}‐NMR based metabolomics and 13 C‐isotope‐assisted labelling studies to track bacterial molecules in the host. Supported by funds from UW‐Madison Graduate School and the School of Veterinary Medicine.