BioProject

Marine regions that experience low dissolved oxygen (DO) from seasonal to long-term time scales, a.k.a. dead zones, are increasing in number and severity around the globe with deleterious effects on ecology and economics. One of the largest of these occurs on the continental shelf of the northern Gulf of Mexico (nGOM) as a result of eutrophication-enhanced bacterioplankton respiration and strong stratification. The effects of this perturbation on microbial assemblages, and therefore the underlying potential for biogeochemical cycling, have only begun to be explored. Here we present 77 high-quality genomes (33 of which are >70% complete) reconstructed from whole community metagenomic data spanning six sites of varying DO concentrations during the 2013 nGOM dead zone. All but two genomes could be classified into 17 named bacterial and archaeal phyla, and many represented the most abundant organisms observed previously in the dead zone (e.g., Thaumarchaeota, Marine group II Euryarchaeota, Synechococcus, Actinobacteria, SAR406). Surprisingly, we recovered near complete genomes from the Candidate Phyla Parcubacteria (OD1), Peregrinibacteria, Latescibacteria (WS3), and ACD39. Metabolic reconstruction predicted roles for many organisms in various phases of nitrogen, carbon, and sulfur cycling. Importantly, many of the most abundant and/or most active taxa were predicted aerobes, suggesting electron donor-based niche partitioning. This work provides an important biogeochemical map for multiple phyla, helping to resolve the impacts of hypoxia on nutrient flow in the dead zone. Less...