Melainabacteria Metabolism Pathways in the Ground Squirrel Gut Microbiome

Abstract

Mammals and their associated microbiomes have been coevolving for 300 million years providing a consistent environment for the microbes and in turn the microbiome supports host health. However, for mammals that hibernate, the internal microbial home environment is radically disrupted with near-freezing temperatures and little or no food availability for up to six months. We know that the gut microbiome undergoes extreme restructuring during hibernation but remains active producing nitrogen and amino acids that facilitate host tissue protein synthesis.The thirteen-lined ground squirrel (Ictidomys tridecemlineatus) uses hibernation to combat nutrient shortage in winter. In preparation for this hibernation state, the ground squirrel transitions from actively functioning to a state of torpor. This transition is marked by a drop in internal body temperature from 37℃ (active state) to about 5 ℃ (torpor state). Throughout winter hibernation, the ground squirrel experiences interbout arousals where body temperature rises back to 37°C for ~24 hours. One bacterial phylum thrives during hibernation, Melainabacter. Melainabacteria are a deep branching phyla of cyanobacteria but are non–photosynthetic and appear to have the ability to survive in warm and cold environmental conditions. During torpor and interbout arousals, levels of Melainabacteria increase to above those of the active state cycle. These complex conditions create an extraordinary set of challenges for the microbes involved in the gut metabolism process. This study reveals the mechanisms behind Melaniabacterial carbohydrate metabolism, carbon fixation, and amino acid metabolism through genomic reconstruction and explores key microbial pathways during hibernation.