Microbial cycling of volatile organic carbon in the marine surface layer

Oregon State University, Corvallis OR

Investigators

Abstract

The prevalence in bacterioplankton genomes of specialized genes for the metabolism of volatile organic compounds is a "smoking gun" that points to a hidden VOC cycle potentially of significant magnitude. With funding provided through this EArly-concept Grant for Exploratory Research (EAGER), researchers at Oregon State University and the University of Colorado at Boulder will gather new evidence about the VOC cycle in the ocean photic zone by: 1) measuring the turnover rates of VOC compounds by plankton communities on a Surface Ocean Lower Atmosphere (SOLAS) cruise, and 2) identifying the organisms and biochemical machinery that mediate VOC oxidation. This research is potentially transformative because quantitative evidence indicating significant VOC cycling would cause an overhaul of carbon cycle models and focus attention on specialized metabolic processes that have received little attention and are poorly characterized. This research is high risk for similar reasons: while mounting evidence points to a significant "hidden carbon cycle", its importance will not be known until its magnitude is measured, and the achievement of this goal requires an investment in specialized knowledge and technology. The project is a collaboration between atmospheric chemists and marine microbiologists who bring together the knowledge and technology needed to solve this problem on a SOLAS cruise and in a laboratory setting. Measurements of the seawater concentrations of VOC compounds (e.g. methanol, formaldehyde, dimethylsulfide, trimethyamine, trimethylamine oxide, acetonitrile, acetone, isoprene, glyoxal, methylglyoxal and acetaldehyde) and turnover rates determined by the incubation of isotopically-labeled compounds with microbial plankton suspensions will provide information about variation in these geochemical processes across a transect that extends from a productive continental shelf to an oligotrophic subtropical gyre. Later the same team will measure the production and oxidation of these compounds by microbial isolates in a controlled setting, focusing on biochemical pathways that oxidize one carbon (C1) units from Oxidized VOC (OVOC) and methylated dissolved organic carbon (MDOC). Comprehensive measurements of microbial diversity in the field and transcriptome responses in the laboratory will set the stage for future research linking VOC cycling to specific organisms, metabolic pathways and genes, and for understanding when, and in response to what selective pressures, the microbial community engages in these processes. Broader Impacts: VOCs play varied and important roles in atmospheric chemistry, acting as precursors for photochemical formation of ozone and aerosol, i.e. two secondary pollutants that also affect the radiative forcing of climate. Information about biological sources and sinks of VOCs in the ocean surface could result in a better understanding of the underlying causes of variation in air/sea VOC fluxes, and potentially could alter predictions about the impact of climate change on ocean surface ecology and air/sea interactions. Additionally, the project will address biochemical mechanisms that underlie VOC cycling and should provide experimental evidence about relevant gene functions. Therefore, revised gene annotations resulting from this work could improve the accuracy of future predictions of VOC metabolism made from genomes and metagenomes. This proposal includes support for postdocs, graduate and undergraduate students and is integrated with the Oregon Institute of Marine Biology's NSF funded Center for Ocean Sciences Education Excellence (COSEE) program, bringing training and experience from this project to community college professors.