Anaerobic microbial degradation of protein and lipid macromolecules in subarctic marine sediment

Microorganisms in marine sediments play major roles in marine biogeochemical cycles by mineralizing substantial quantities of organic matter from decaying cells. Proteins and lipids are abundant components of necromass, yet microorganisms that degrade them remain understudied. Here, we revealed identities, trophic interactions and genomic features of microorganisms that degraded C-labelled proteins and lipids in cold anoxic microcosms with sulfidic subarctic marine sediment. Supplemented proteins and lipids were rapidly fermented to various volatile fatty acids within five days. DNA-stable isotope probing (SIP) suggested was an important primary degrader of proteins, and members were important primary degraders of both proteins and lipids. Closely related populations, as represented by distinct 16S rRNA gene variants, differentially utilized either proteins or lipids. DNA-SIP also showed C-labeling of various within ten days, indicating trophic transfer of carbon to putative sulfate-reducers. Metagenome-assembled genomes revealed the primary hydrolyzers encoded secreted peptidases or lipases, and enzymes for catabolism of protein or lipid degradation products. were prevalent in diverse marine sediments, suggesting they are important players in organic carbon processing . Together, this study provides an improved understanding of the metabolic processes and functional partitioning of necromass macromolecules among microorganisms in the seafloor.