Genome-resolved metaproteomics decodes the microbial and viral contributions to coupled carbon and nitrogen cycling in river sediments
Authors: Rodríguez-Ramos Josué A. , Borton Mikayla A. , McGivern Bridget B. , Smith Garrett J. , Solden Lindsey M. , Shaffer Michael , Daly Rebecca A. , Purvine Samuel O. , Nicora Carrie D. , Eder Elizabeth K. , Lipton Mary , Hoyt David W. , Stegen James C. , Wrighton Kelly C. 
Published: March 2022

Rivers have a significant role in global carbon and nitrogen cycles, serving as a nexus for nutrient transport between terrestrial and marine ecosystems. Although rivers have a small global surface area, they contribute substantially to global greenhouse gas emissions through microbially mediated processes within the river hyporheic zone. Despite this importance, microbial roles in these climatically relevant systems are mostly inferred from 16S rRNA amplicon surveys, which are not sufficiently resolved to inform biogeochemical models. To survey the metabolic potential and gene expression underpinning carbon and nitrogen biogeochemical cycling in river sediments, we collected an integrated dataset of over 30 metagenomes, metaproteomes, and paired metabolomes. We reconstructed over 500 microbial metagenome assembled genomes (MAGs), which we dereplicated into 55 unique genomes spanning 12 bacterial and archaeal phyla. We also reconstructed 2482 viral genomic contigs, which were dereplicated into 111 viral MAGs >10kb in size. As a result of integrating gene expression data with geochemical and metabolite data, we created a conceptual model that uncovers new roles for microorganisms in organic matter decomposition, carbon sequestration, nitrogen mineralization, nitrification, and denitrification. Integrated through shared resource pools of ammonium, carbon dioxide, and inorganic nitrogen we show how these metabolic pathways could ultimately contribute to carbon dioxide and nitrous oxide fluxes from hyporheic sediments. Further, by linking viral genomes to these active microbial hosts, we provide some of the first insights into viral modulation of river sediment carbon and nitrogen cycling.

Importance

Here we created HUM-V (Hyporheic Uncultured Microbial and Viral), an annotated microbial and viral genome catalog that captures the strain and functional diversity encoded in river sediments. Demonstrating its utility, this genomic inventory encompasses multiple representatives of the most dominant microbial and archaeal phyla reported in river sediments and provides novel viral genomes that can putatively infect these. Furthermore, we used HUM-V to recruit gene expression data to decipher the functional activities of these genomes and reconstruct their active roles in river sediment biogeochemical cycling. We show the power of genome resolved, multi-omics to uncover the organismal interactions and chemical handoffs shaping an intertwined carbon and nitrogen metabolic network and create a framework that can be extended to other river sediments. The accessible microbial and viral genomes in HUM-V will serve as a community resource to further advance more untargeted, activity-based measurements in these and related freshwater terrestrial-aquatic ecosystems.