Award: OCE-1336082

Collaborative Research: Genetic and Metabolic Signatures of Marine Microorganisms in Oxygen Depleted and Varying Geochemical Seascapes (MetaOmics in the Cariaco Basin) Approximately 10% of global oceans are experiencing moderate to severe oxygen depletion, with consequent significant impacts on nitrogen and sulfur cycling by microorganisms. Oxygen-depleted water columns shift microbial communities and their activities toward processes that lead to increased release of climate-active trace gases, and depletion of bioavailable nitrogen, which can have detrimental effects on ocean primary production. The overall goal of this work was to examine microbial diversity (Bacteria, Archaea, and Eukarya, plus viruses) and processes along an oxygen gradient in a well-constrained ecosystem (Cariaco Basin, Venezuela) and to determine if partitioning of microbial processes occurs between the particle-associated and free-living fractions. Our hypothesis was that cryptic sulfur cycle and close coupling of nitrogen and sulfur cyling are fueling the high chemoautotrophy and heterotrophic productivity in oxygen-depleted waters. We produced data on taxonomic diversity (based on SSU rRNA iTAGs), microbial functional potential (metagenome libraries and qPCR of functional genes), and gene activity (metatranscriptome libraries and RT-qPCR of functional genes), in two seasons, in the particle-associated and free-living fractions, and at six primary sampling depths along oxygen and chemical gradient in the Cariaco water column. We interpreted these data in the context of hydrographic, geochemical, and microbial ecological data, including observed rates of key microbial processes along the redoxcline. Particle-associated and free-living communities were found to be functionally different. Evidence was found for a cryptic sulfur cycle in suboxic/anoxic waters, as was close metabolic coupling of sulfur and nitrogen cycles. Both denitrification and annamox were active nitrogen removing processes in the Cariaco Basin, while occurring in separate niches. Denitrifiers are primarily particle-associated and responsive to NO3- pulses potentially provided by horizontal intrusions in this system. Anammox organisms were primarily free-living and generally unresponsive to DIN pulses. Bacterial assemblage composition across the redoxcline clearly underwent abrupt changes that were detected in 2009 in the course of the Cariaco Ocean Time-Series program. The dominant putative chemoautotrophs in this layer appeared to have switched from e-proteobacteria to g-proteobacteria after the 2009 transition. During the observation period, vertical distributions of H2S, NH4+, O2, NO3-, and NO2- and water density structure changed significantly through the redoxcline. Variations in vertical fluxes of oxidants (O2, NO3-, and NO2-) and reductants (H2S, S2O32, SO32-, S0, NH4+) appear to be key in niche partitioning between e- and g-proteobacteria and may explain the ecosystem state change in ways that are yet to be discovered. Forty-eight metagenomes and forty-eight metatranscriptomes have been deposited to public databases, as well as 141 iTAG libraries. Two publications by our group and two presentations by Edgcomb at international events hosted by the Scientific Committee on Ocean Research highlighted this work, pointed out the biases and artifacts introduced by traditional Niskin sampling for RNA-based studies, and made the case for the need for technological advances to provide cost-effective means for rapid in situ sample collection and preservation. This project framed the PhD thesis for one graduate student, Elizabeth Suter, Stony Brook University (SBU), and the work of one Postdoctoral Investigator, Maria Pachiadaki, WHOI. In addition, three high school students were trained during summer projects, and at least two high school students annually (2016-17, 2015-16, 2014-15, 2013-14) for Science Fair Projects around the theme of effects of oxygen depletion on marine microbial ecology. Edgcomb taught groups of ~20 high school students annually in each of summers 2014-2017 during 2-day intensive workshops on marine microbiology and oxygen depletion, through the Weston Schools Advanced Biotechnology Institute. Last Modified: 08/23/2017 Submitted by: Virginia P Edgcomb