Biology subjects

Chiang, E.

Publications and source records attributed to Chiang, E..

3 recordsLinked to original sources

bioRxiv2025

Host-microbe mutualism drives urea carbon salvage and acetogenesis during hibernation

2.Hibernation is a seasonal survival strategy employed by certain mammals that, through torpor use, reduces overall energy expenditure and permits long-term fasting. Although fasting solves the challenge of winter food scarcity, it also removes dietary carbon, a critical biomolecular building block. Here, we demonstrate a process of urea carbon salvage (UCS) in hibernating 13-lined ground squirrels, whereby urea carbon is reclaimed through gut microbial ureolysis and used in reductive acetogenesis to produce acetate, a short-chain fatty acid (SCFA) of major value to the host and its gut microbiota. We find that urea carbon incorporation into acetate is more efficient during hibernation than the summer active season, and that while both host and gut microbes oxidize acetate for energy supply throughout the year, the hosts ability to absorb and oxidize acetate is highest during hibernation. Metagenomic analysis of the gut microbiome indicates that genes involved in the degradation of gut mucins, an abundant endogenous nutrient, are retained during hibernation. The hydrogen disposal associated with reductive acetogenesis from urea carbon helps facilitate this mucin degradation by providing a luminal environment that sustains fermentation, thereby generating SCFAs and other metabolites usable by both the host and its gut microbes. Our findings introduce UCS as a mechanism that enables hibernating squirrels and their gut microbes to exploit two key endogenous nutrient sources - urea and mucins - in the resource-limited hibernation season. 3. SIGNIFICANCE STATEMENTWhen food becomes scarce during winter, hibernating mammals induce torpor to minimize energy demands and enable monthslong fasting. However, fasting eliminates the intake of essential nutrients such as carbon. We identified a two-step microbial-host interaction in ground squirrels - urea carbon salvage (UCS) - which counters carbon limitation by salvaging carbon from waste urea. Through activities of ureolytic and acetogenic bacteria, urea-derived CO2 is reduced by free hydrogen to form acetate, whose oxidation provides energy for gut microbes and the host. This process also helps maintain a permissive environment for fermentation of other host-derived, energy-dense compounds such as mucins. UCS broadens our understanding of host-microbe mutualism under extreme nutritional constraints and may represent a widespread adaptation among fasting mammals.

physiology↗

bioRxiv2021

Urea nitrogen recycling via gut symbionts increases in hibernators over the winter fast

Hibernation is a mammalian strategy that uses metabolic plasticity to reduce energy demands and enable long-term fasting. Fasting mitigates winter food scarcity but eliminates dietary nitrogen, jeopardizing body protein balance. Here, we reveal gut microbiome-mediated urea nitrogen recycling in hibernating 13-lined ground squirrels (TLGS). Ureolytic gut microbes incorporate urea nitrogen into organic compounds that are absorbed by the host, with the nitrogen reincorporated into the TLGS protein pool. Urea nitrogen recycling is greatest after prolonged fasting in late winter, when urea transporter abundance in gut tissue and urease gene abundance in the microbiome are highest. These results reveal a functional role for the gut microbiome in hibernation and suggest mechanisms by which urea nitrogen recycling contributes to protein balance in other monogastric animals, including humans. One Sentence SummaryGround squirrels and their gut symbionts benefit from urea nitrogen recycling throughout hibernation.

physiology↗

bioRxiv2017

Microhabitats shape diversity-productivity relationships in freshwater bacterial communities

Eukaryotic communities commonly display a positive relationship between biodiversity and ecosystem function (BEF) but the results have been mixed when assessed in bacterial communities. Habitat heterogeneity, a factor in eukaryotic BEFs, may explain these variable observations but it has not been thoroughly evaluated in bacterial communities. Here, we examined the impact of habitat on the relationship between diversity assessed based on richness, evenness, or phylogenetic diversity, and heterotrophic productivity. We sampled co-occurring free-living (more homogenous) and particle-associated (more heterogeneous) bacterial habitats in a freshwater, estuarine lake. Diversity measures, and not environmental variables, were the best predictors of particle-associated heterotrophic production. There was a strong, positive, linear relationship between particle-associated bacterial richness and heterotrophic productivity that strengthened with evenness. There were no observable BEF trends in free-living bacterial communities. Across both habitats, communities with more phylogenetically related taxa had higher per-capita heterotrophic production than communities of phylogenetically distantly related taxa. Our findings show that heterotrophic bacterial productivity is positively correlated with evenness and richness, negatively with phylogenetic diversity, and that BEF relationships are contingent on microhabitats. Our work adds to the understanding of the highly distinct contributions to community diversity and ecosystem functioning contributed by bacteria in free-living and particle-associated aquatic habitats.

ecology↗