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Summary: Plants and phytoplankton are natural sources of the volatile organic compounds (VOCs) acetone and isoprene, which are reactive and can alter atmospheric chemistry. In earlier research we reported that, when co‐cultured with a diatom, the marine bacterium Pelagibacter (strain HTCC1062; 'SAR11 clade') reduced the concentration of compounds tentatively identified as acetone and isoprene. In this study, experiments with Pelagibacter monocultures confirmed that these cells are capable of metabolizing acetone and isoprene at rates similar to bacterial communities in seawater and high enough to consume substantial fractions of the total marine acetone and isoprene budgets if extrapolated to global SAR11 populations. Homologues of an acetone/cyclohexanone monooxygenase were identified in the HTCC1062 genome and in the genomes of a wide variety of other abundant marine taxa, and were expressed at substantial levels (c. 10−4 of transcripts) across TARA oceans metatranscriptomes from ocean surface samples. The HTCC1062 genome lacks the canonical isoprene degradation pathway, suggesting an unknown alternative biochemical pathway is used by these cells for isoprene uptake. Fosmidomycin, an inhibitor of bacterial isoprenoid biosynthesis, blocked HTCC1062 growth, but the cells were rescued when isoprene was added to the culture, indicating SAR11 cells may be capable of synthesizing isoprenoid compounds from exogenous isoprene. [ABSTRACT FROM AUTHOR]

Summary: Volatile organic compounds (VOCs) produced by phytoplankton are molecules with high vapor pressures that can diffuse across cell membranes into the environment, where they become public goods. VOCs likely comprise a significant component of the marine dissolved organic carbon (DOC) pool utilized by microorganisms, but they are often overlooked as growth substrates because their diffusivity imposes analytical challenges. The roles of VOCs in the growth of the photoautotrophic diatom Thalassiosira pseudonana and heterotrophic bacterium Pelagibacter sp. HTCC1062 (SAR11) were examined using co‐cultures and proton‐transfer reaction time‐of‐flight mass spectrometry. VOCs at 82 m/z values were produced in the cultures, and the concentrations of 9 of these m/z values changed in co‐culture relative to the diatom monoculture. Several of the m/z values were putatively identified, and their metabolism by HTCC1062 was confirmed by measuring ATP production. Diatom carbon fixation rates in co‐culture with HTCC1062 were 20.3% higher than the diatom monoculture. Removal of VOCs from the T. pseudonana monoculture using a hydrocarbon trap caused a similar increase in carbon fixation (18.1%). These results show that a wide range of VOCs are cycled in the environment, and the flux of VOCs from phytoplankton to bacterioplankton imposes a large and unexpected tax on phytoplankton photosynthesis. [ABSTRACT FROM AUTHOR]

Acetaldehyde, methanol, acetone, and isoprene are important reactive volatile organic compounds (VOCs) in the oceans that partition to the atmosphere in significant amounts. Reports of potentially high rates of VOC turnover in the North Atlantic suggested that both biotic and abiotic processes are involved. The biological basis for VOC cycling by ocean plankton is unknown, but is potentially important because of VOC contributions to carbon cycle budgets and atmospheric chemistry. We designed dynamic stripping chambers that coupled to a proton transfer reaction mass spectrometer to measure VOC production and consumption by cultured phytoplankton and bacterioplankton. The diatom, Thalassiosira pseudonana, produced acetaldehyde in a light-dependent manner. Acetaldehyde was oxidized by the chemoheterotrophic bacterium, Pelagibacter, at rates that suggest that most acetaldehyde is recycled in the ocean before escaping to the atmosphere. These results show that field observations of acetaldehyde turnover reported previously could be explained by biological activity. Rates of production by phytoplankton cultures of methanol, acetone, and isoprene were also measured. These findings support the conclusion that VOCs are a conduit for carbon transfer directly from phytoplankton to bacterioplankton, with the remainder available for escape to the atmosphere. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) comprise a vast pool of low molecular weight and rapidly diffusible chemicals that are emitted from all cells as well as by photolysis of dissolved organic matter and burning of fossil fuels. In the ocean, VOCs are an important component of the marine carbon cycle, serving as plankton growth products and substrates and also as info-chemicals that influence phytoplankton life cycles. When VOCs are emitted from the ocean into the atmosphere, they alter Earth's radiative budget through oxidation reactions and secondary aerosol formation. Marine phytoplankton are the primary biotic source of marine VOCs, many of which are exploited as nutrient resources by ubiquitous bacterioplankton that have evolved specific mechanisms to consume these compounds. Thus, the balance of VOC production and consumption exerts control on the concentrations of dissolved VOCs at the sea-air interface. Current simulations of atmospheric chemistry do not take into account biological controls of dissolved VOCs. Linkages between phytoplankton communities, VOC composition, and surface ocean properties are promising avenues for improving the next generation of chemical transport models that quantify and predict VOC emissions. We suggest that VOC accumulation may be predictable by identifying periods when plankton communities are disrupted by biological or physical processes. Layered models that use remote sensing and ocean physics to measure the states and trajectories of plankton assemblages have promise for predicting ocean sea-air VOC transfer. [ABSTRACT FROM AUTHOR]