Meeting Abstract
Arctic ground squirrels (AGS) are hibernation extremophiles, spending up to 9 months annually in torpor, subsisting on endogenous body reserves of lipid and protein. Urea-nitrogen salvage (UNS)—the diffusion of urea into the gut, its degradation by ureolytic gut microbes, and the subsequent incorporation of microbially-liberated urea-N (MLUN) by the host—is posited as an important N-conservation mechanism of hibernators; however, little is known about the extent to which MLUN contributes to host synthetic processes, the identity, number or activity of ureolytic microbes in the gut, or how these aspects change seasonally. Therefore, we injected squirrels with either unlabeled or 15N/13C-labeled urea periodically across their annual cycle. The magnitude of gut ureolysis was assessed via quantification of 13CO2 in breath. To determine host use of MLUN, tissues were collected for analysis of δ15N. Cecal samples were collected to enumerate ureolytic microbes and determine expression of urease genes, and fecal and cecal samples were collected to isolate and characterize ureolytic bacteria. Enrichment of 13CO2 in breath indicates active ureolytic bacteria in the gut in both hibernation and summer euthermia, and several taxonomically diverse ureolytic bacteria were isolated and identified. We further analyzed tissues for δ15N, and enumerated ureolytic bacteria and expression of urease genes in the gut. Our results indicate that AGS contain a diversity of ureolytic gut bacteria that are active across the annual cycle. Differences in δ15N of control vs experimental AGS will show the degree to which AGS incorporate MLUN, results that hold the potential to show the importance of UNS in lean mass restructuring during hibernation.
