The fecal microbiota of free-ranging brown bears was collected during their active phase (summer) and hibernation (winter). Germfree mice were colonized with the seasonal bear microbiota. Bear fecal and mouse cecal microbiota were analyzed using 16S profiling.. The gut microbiota modulates energy metabolism in the hibernating brown bear Ursus arctos

Hibernation is an adaptation that helps many animals to conserve energy during food shortage in winter. Brown bears double their fat depots during summer and use these stored lipids during hibernation. Although bears seasonally become obese, they remain metabolically healthy. We analyzed the microbiota of free-ranging brown bears during their active phase and hibernation. Compared with the active phase, the hibernation microbiota had reduced diversity, reduced levels of Firmicutes and Actinobacteria, and increased levels of Bacteroidetes. Several metabolites involved in lipid metabolism including triglycerides, cholesterol and bile acids were also affected by hibernation. Transplantation of the bear microbiota from summer and winter to germ-free mice transferred some of the seasonal metabolic features and demonstrated that the summer microbiota promoted adiposity without impairing glucose tolerance, suggesting that seasonal variation in the microbiota may contribute to host energy metabolism in the hibernating brown bear.

冬眠是诸多动物在冬季食物匮乏时期留存能量的适应性策略。棕熊会在夏季将体内脂肪储备翻倍，并在冬眠期间利用这些储存的脂质。尽管棕熊会随季节出现肥胖现象，但它们的代谢状态仍保持健康。本研究对野生棕熊在活动期与冬眠期的微生物组（microbiota）进行了分析。与活动期相比，冬眠期的微生物组多样性降低，厚壁菌门（Firmicutes）与放线菌门（Actinobacteria）的相对丰度下降，而拟杆菌门（Bacteroidetes）的相对丰度则有所上升。多项参与脂质代谢的代谢物，包括甘油三酯、胆固醇与胆汁酸，也会因冬眠状态发生改变。将夏季与冬季的棕熊微生物组移植到无菌小鼠（germ-free mice）体内后，部分季节性代谢特征得以成功转移；实验结果显示，夏季微生物组可促进小鼠体脂积累但未损害其糖耐量，这表明微生物组的季节性变化或许参与调控冬眠棕熊的宿主能量代谢过程。