Longnecker Krista

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  • Preprint
    Identification of possible source markers in marine dissolved organic matter using ultrahigh resolution mass spectrometry
    ( 2009-04-30) Kujawinski, Elizabeth B. ; Longnecker, Krista ; Blough, Neil V. ; Del Vecchio, Rossana ; Finlay, Liam ; Kitner, Joshua B. ; Giovannoni, Stephen J.
    Marine dissolved organic matter (DOM) is one of the most heterogeneous and largest pools of reactive carbon on earth, rivaling in mass the carbon in atmospheric carbon dioxide. Nevertheless, the molecular-level composition of marine DOM has eluded detailed description, impeding inquiry into the specific mechanisms that add or remove compounds from the DOM pool. Here we describe the molecular-level composition of C18-extracted DOM along an east-west transect of the North Atlantic Ocean. We examine the changes in DOM composition along this transect with ultrahigh resolution mass spectrometry and multivariate statistics. We use indicator species analysis (ISA) to identify possible source markers for photochemical degradation and heterotrophic bacterial metabolism. The inclusion of ISA in statistical evaluation of DOM mass spectral data allows investigators to determine the m/z values associated with significant changes in DOM composition. With this technique, we observe indicator m/z values in estuarine water that may represent components of terrestrially-derived chromophoric DOM subject to photo-chemical degradation. We also observe a unique set of m/z values in surface seawater and show that many of these are present in pure cultures of the marine α-proteobacterium Candidatus Pelagibacter ubique when grown in natural seawater. These findings indicate that a complex balance of abiotic and biotic processes controls the molecular composition of marine DOM to produce signatures that are characteristic of different environments.
  • Preprint
    Fate of dispersants associated with the Deepwater Horizon oil spill
    ( 2011-01-05) Kujawinski, Elizabeth B. ; Kido Soule, Melissa C. ; Valentine, David L. ; Boysen, Angela K. ; Longnecker, Krista ; Redmond, Molly C.
    Response actions to the Deepwater Horizon oil spill included the injection of ~771,000 gallons (2,900,000 L) of chemical dispersant into the flow of oil near the seafloor. Prior to this incident, no deepwater applications of dispersant had been conducted and thus no data exists on the environmental fate of dispersants in deepwater. We used ultrahigh resolution mass spectrometry and liquid chromatography with tandem mass spectrometry (LC/MS/MS) to identify and quantify one key ingredient of the dispersant, the anionic surfactant DOSS (dioctyl sodium sulfosuccinate), in the Gulf of Mexico deepwater during active flow and again after flow had ceased. Here we show that DOSS was sequestered in deepwater hydrocarbon plumes at 1000-1200m water depth and did not intermingle with surface dispersant applications. Further, its concentration distribution was consistent with conservative transport and dilution at depth and it persisted up to 300 km from the well, 64 days after deepwater dispersant applications ceased. We conclude that DOSS was selectively associated with the oil and gas phases in the deepwater plume, yet underwent negligible, or slow, rates of biodegradation in the affected waters. These results provide important constraints on accurate modeling of the deepwater plume and critical geochemical contexts for future toxicological studies.
  • Preprint
    Dissolved organic matter produced by Thalassiosira pseudonana
    ( 2014-10) Longnecker, Krista ; Kido Soule, Melissa C. ; Kujawinski, Elizabeth B.
    Phytoplankton are significant producers of dissolved organic matter (DOM) in marine ecosystems but the identity and dynamics of this DOM remain poorly constrained. Knowledge on the identity and dynamics of DOM are crucial for understanding the molecular-level reactions at the base of the global carbon cycle. Here we apply emerging analytical and computational tools from metabolomics to investigate the composition of DOM produced by the centric diatom Thalassiosira pseudonana. We assessed both intracellular metabolites within T. pseudonana (the endo-metabolome) and extracellular metabolites released by T. pseudonana (the exo-metabolome). The intracellular metabolites had a more variable composition than the extracellular metabolites. We putatively identified novel compounds not previously associated with T. pseudonana as well as compounds that have previously been identified within T. pseudonana’s metabolic capacity (e.g. dimethylsulfoniopropionate and degradation products of chitin). The resulting information will provide the basis for future experiments to assess the impact of T. pseudonana on the composition of dissolved organic matter in marine environments.
  • Preprint
    Using stable isotope probing to characterize differences between free-living and sediment-associated microorganisms in the subsurface
    ( 2012-04-24) Longnecker, Krista ; Kujawinski, Elizabeth B.
    Aquifers are subterranean reservoirs of freshwater with heterotrophic bacterial communities attached to the sediments and free-living in the groundwater. In the present study, mesocosms were used to assess factors controlling the diversity and activity of the subsurface bacterial community. The assimilation of 13C, derived from 13C-acetate, was monitored to determine whether the sediment-associated and free-living bacterial community would respond similarly to the presence of protozoan grazers. We observed a dynamic response in the sediment-associated bacterial community and none in the free-living community. The disparity in these observations highlights the importance of the sediment-associated bacterial community in the subsurface carbon cycle.
  • Preprint
    Molecular characterization of dissolved organic matter associated with the Greenland ice sheet
    ( 2010-03-16) Bhatia, Maya P. ; Das, Sarah B. ; Longnecker, Krista ; Charette, Matthew A. ; Kujawinski, Elizabeth B.
    Subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial-interglacial timescales. The likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores. We examined the composition of carbon pools associated with different regions of the Greenland ice sheet (subglacial, supraglacial, proglacial) in order to elucidate the type of dissolved organic matter (DOM) present in the subglacial discharge over a melt season. Electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes. Specifically, a larger proportion of protein-like compounds were observed in the supraglacial samples and in the early melt season (spring) subglacial discharge. In contrast, the late melt season (summer) subglacial discharge contained a greater fraction of lignin-like and other material presumably derived from underlying vegetation and soil. These results suggest (1) that the majority of supraglacial DOM originates from autochthonous microbial processes on the ice sheet surface, (2) that the subglacial DOM contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism, and (3) that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season. These conclusions are consistent with the hypothesis that, given sufficient time (e.g., overwinter storage), resident subglacial microbial communities may oxidize terrestrial material beneath the Greenland ice sheet.
  • Preprint
    The molecular products and biogeochemical significance of lipid photooxidation in West Antarctic surface waters
    ( 2018-04) Collins, James R. ; Fredricks, Helen F. ; Bowman, Jeff S. ; Ward, Collin P. ; Moreno, Carly ; Longnecker, Krista ; Marchetti, Adrian ; Hansel, Colleen M. ; Ducklow, Hugh W. ; Van Mooy, Benjamin A. S.
    The seasonal depletion of stratospheric ozone over the Southern Hemisphere allows abnormally high doses of ultraviolet radiation (UVR) to reach surface waters of the West Antarctic Peninsula (WAP) in the austral spring, creating a natural laboratory for the study of lipid photooxidation in the shallow mixed layer of the marginal ice zone. The photooxidation of lipids under such conditions has been identified as a significant source of stress to microorganisms, and short-chain fatty acids altered by photochemical processes have been found in both marine aerosols and sinking marine particle material. However, the biogeochemical impact of lipid photooxidation has not been quantitatively compared at ecosystem scale to the many other biological and abiotic processes that can transform particulate organic matter in the surface ocean. We combined results from field experiments with diverse environmental data, including high-resolution, accurate-mass HPLC-ESI-MS analysis of lipid extracts and in situ measurements of ultraviolet irradiance, to address several unresolved questions about lipid photooxidation in the marine environment. In our experiments, we used liposomes — nonliving, cell-like aggregations of lipids — to examine the photolability of various moieties of the intact polar diacylglycerol (IP-DAG) phosphatidylcholine (PC), a structural component of membranes in a broad range of microorganisms. We observed significant rates of photooxidation only when the molecule contained the polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA). As the DHA-containing lipid was oxidized, we observed the steady ingrowth of a diversity of oxylipins and oxidized IP-DAG; our results suggest both the intact IPDAG the degradation products were amenable to heterotrophic assimilation. To complement our experiments, we used an enhanced version of a new lipidomics discovery software package to identify the lipids in water column samples and in several diatom isolates. The galactolipid digalactosyldiacylglycerol (DGDG), the sulfolipid sulfoquinovosyldiacylglycerol (SQDG) and the phospholipids PC and phosphatidylglycerol (PG) accounted for the majority of IP-DAG in the water column particulate (≥ 0.2 μm) size fraction; between 3.4 and 5.3 % of the IP-DAG contained fatty acids that were both highly polyunsaturated (i.e., each containing ≥ 5 double bonds). Using a broadband apparent quantum yield (AQY) that accounted for direct and Type I (i.e., radical-mediated) photooxidation of PUFA-containing IP-DAG, we estimated that 0.7 ± 0.2 μmol IP-DAG m-2 d-1 (0.5 ± 0.1 mg C m-2 d-1) were oxidized by photochemical processes in the mixed layer. This rate represented 4.4 % (range, 3-21 %) of the mean bacterial production rate measured in the same waters immediately following the retreat of the sea ice. Because our liposome experiments were not designed to account for oxidation by Type II photosensitized processes that often dominate in marine phytodetritus, our rate estimates may represent a sizeable underestimate of the true rate of lipid photooxidation in the water column. While production of such diverse oxidized lipids and oxylipins has been previously observed in terrestrial plants and mammals in response to biological stressors such as disease, we show here that a similar suite of molecules can be produced via an abiotic process in the environment and that the effect can be commensurate in magnitude with other ecosystem-scale biogeochemical processes.
  • Preprint
    Molecular signature of organic nitrogen in septic-impacted groundwater
    ( 2014-08) Arnold, William A. ; Longnecker, Krista ; Kroeger, Kevin D. ; Kujawinski, Elizabeth B.
    Dissolved inorganic and organic nitrogen levels are elevated in aquatic systems due to anthropogenic activities. Dissolved organic nitrogen (DON) arises from various sources, and its impact could be more clearly constrained if specific sources were identified and if the molecular level composition of DON were better understood. In this work, the pharmaceutical carbamazepine was used to identify septic-impacted groundwater in a coastal watershed. Using ultrahigh resolution mass spectrometry data, the nitrogen-containing features of the dissolved organic matter in septic-impacted and non-impacted samples were compared. The septic impacted groundwater samples have a larger abundance of nitrogen-containing formulas. Impacted samples have additional DON features in the regions ascribed as ‘protein-like’ and ‘lipid-like’ in van Krevelen space and have more intense nitrogen-containing features in a specific region of a carbon versus mass plot. These features are potential indicators of dissolved organic nitrogen arising from septic effluents, and this work suggests that ultrahigh resolution mass spectrometry is a valuable tool to identify and characterize sources of DON.
  • Dataset
    Total organic sulfur (TOS) collected from Niskin bottle samples on R/V Knorr cruise KN210-04 in the Western Atlantic Ocean between Uruguay and Barbados from March to May 2013 (Deep Atlantic DOM project)
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-03-15) Kujawinski, Elizabeth ; Longnecker, Krista
    This dataset contains the concentration of total organic sulfur (TOS) in seawater from samples collected during the R/V Knorr cruise KN210-04 between 29 Mar 2013 and 06 May 2013 along the eastern coast of South America. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/745536
  • Article
    Benthic exometabolites and their ecological significance on threatened Caribbean coral reefs
    (Springer, 2022-10-17) Weber, Laura ; Soule, Melissa Kido ; Longnecker, Krista ; Becker, Cynthia C. ; Huntley, Naomi ; Kujawinski, Elizabeth B. ; Apprill, Amy
    Benthic organisms are the architectural framework supporting coral reef ecosystems, but their community composition has recently shifted on many reefs. Little is known about the metabolites released from these benthic organisms and how compositional shifts may influence other reef life, including prolific microorganisms. To investigate the metabolite composition of benthic exudates and their ecological significance for reef microbial communities, we harvested exudates from six species of Caribbean benthic organisms including stony corals, octocorals, and an invasive encrusting alga, and subjected these exudates to untargeted and targeted metabolomics approaches using liquid chromatography-mass spectrometry. Incubations with reef seawater microorganisms were conducted to monitor changes in microbial abundances and community composition using 16 S rRNA gene sequencing in relation to exudate source and three specific metabolites. Exudates were enriched in amino acids, nucleosides, vitamins, and indole-based metabolites, showing that benthic organisms contribute labile organic matter to reefs. Furthermore, exudate compositions were species-specific, and riboflavin and pantothenic acid emerged as significant coral-produced metabolites, while caffeine emerged as a significant invasive algal-produced metabolite. Microbial abundances and individual microbial taxa responded differently to exudates from stony corals and octocorals, demonstrating that exudate mixtures released from different coral species select for specific bacteria. In contrast, microbial communities did not respond to individual additions of riboflavin, pantothenic acid, or caffeine. This work indicates that recent shifts in benthic organisms alter exudate composition and likely impact microbial communities on coral reefs.
  • Dataset
    Inorganic and organic nutrient data from Niskin bottles from R/V Knorr cruise KN210-04 in the Western Atlantic Ocean between Uruguay and Barbados in 2013 (Deep Atlantic DOM project)
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-11-20) Kujawinski, Elizabeth ; Longnecker, Krista
    Inorganic and organic nutrient data from Niskin bottles from the KN210-04 cruise. Data include concentration of: phosphate, nitrate+nitrite, silicate, nitrite, ammonium, non-purgeable organic carbon, and total nitrogen. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/473296
  • Dataset
    Processed CTD data from all sensors mounted on the rosette from R/V Knorr cruise KN210-04 in the Western Atlantic Ocean between Uruguay and Barbados in 2013 (Deep Atlantic DOM project)
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-11-21) Kujawinski, Elizabeth ; Longnecker, Krista
    Processed CTD data from all sensors mounted on the rosette from the KN210-04 cruise. Data include temperature, salinity, dissolved oxygen, fluorometry, turbidity, PAR, and SPAR. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/481164
  • Preprint
    Characterization of dissolved organic matter in Lake Superior and its watershed using ultrahigh resolution mass spectrometry
    ( 2011-11-14) Minor, Elizabeth C. ; Steinbring, Carla J. ; Longnecker, Krista ; Kujawinski, Elizabeth B.
    With the advent of ultrahigh resolution mass spectrometry, recent studies have begun to resolve molecular-level relationships between terrestrial and aquatic dissolved organic matter (DOM) in rivers, estuaries, mangrove swamps and their receiving oceans and lakes. Here, we extend ultrahigh resolution mass spectrometry techniques to Lake Superior, the largest freshwater lake in the world by area. Solid-phase extracted samples from the western arm of the lake and its watershed, including swamp, creek, river, lake-river confluence and offshore lake sites were compared using electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Results were analyzed using cluster analysis and van Krevelen diagrams. Chemical similarity appears related to hydrological proximity, terrestrial impact and flow conditions. For example, higher and lower flow samples from the same stream differ from one another. Toivola Swamp, Lake Superior, and the south shore river have diverse arrays of unique molecular formulae.relative to the north shore river and stream sampled in this data set. Lake Superior’s unique elemental formulae, relative to its watershed samples, are primarily in the lignin-like and reduced hydrocarbon regions of van Krevelen diagrams. ESI-amenable Lake Superior DOM also has a higher proportion of formulae containing nitrogen or sulfur relative to the other samples. The degree of overlap among formulae within our data set is consistent with previous ESI FT-ICR-MS characterization of terrestrial, estuarine and marine OM. There appears to be a conserved portion of formulae across natural OM samples, perhaps because these compounds are intrinsically refractory or because they are commonly generated as products of natural reworking processes.
  • Preprint
    Dissolved organic matter in newly formed sea ice and surface seawater
    ( 2015-08-25) Longnecker, Krista
    Changes in sea ice in the Arctic will have ramifications on regional and global carbon cycling. Research to date has primarily focused on the regional impacts to biological activity and global impacts on atmospheric processes. The current project considers the molecular-level composition of organic carbon within sea ice compared to the organic matter in seawater. The project revealed that the composition of organic matter within sea ice was more variable than the composition of organic matter within the surface ocean. Furthermore, sea ice samples presented two distinct patterns in the composition of organic matter with a portion of the sea ice samples containing protein-like organic matter. Yet, the samples were collected in the early winter period when little biological activity is expected. Thus, one hypothesis is that physical processes acting during the formation of sea ice selectively transferred organic matter from seawater into sea ice. The present project expands our understanding of dissolved organic matter in sea ice and surface seawater and thereby increases our knowledge of carbon cycling in polar regions.
  • Preprint
    Using network analysis to discern compositional patterns in ultrahigh resolution mass spectrometry data of dissolved organic matter
    ( 2016-08) Longnecker, Krista ; Kujawinski, Elizabeth B.
    Marine dissolved organic matter (DOM) has long been recognized as a large and dynamic component of the global carbon cycle. Yet, DOM is chemical varied and complex and these attributes present challenges to the researchers interested in addressing questions about the role of DOM in global biogeochemical cycles. This project analyzed organic matter extracts from seawater with direct infusion with electrospray ionization into a Fourier transform ion cyclotron resonance mass spectrometer (ESI FT-ICR-MS). We used network analysis to quantify the number of chemical transformations between mass-to-charge values in each sample. The network of chemical transformations was calculated using the MetaNetter plug-in within Cytoscape. The chemical transformations serve as markers for the shared structural characteristics of compounds within complex dissolved organic matter. Network analysis revealed that transformations involving selected sulfur-containing moieties and isomers of amino acids were more prevalent in the deep sea than in the surface ocean. Common chemical transformations were not significantly different between the deep sea and surface ocean. Network analysis complements existing computational tools used to analyze ultrahigh resolution mass spectrometry data. This combination of ultrahigh resolution mass spectrometry with novel computational tools has identified new potential building blocks of organic compounds in the deep sea, including the unexpected importance of dissolved organic sulfur components. The method described here can be readily applied by researchers to analyze heterogeneous and complex dissolved organic matter.
  • Article
    Extracellular reef metabolites across the protected Jardines de la Reina, Cuba Reef System
    (Frontiers Media, 2020-12-14) Weber, Laura ; Armenteros, Maickel ; Kido Soule, Melissa C. ; Longnecker, Krista ; Kujawinski, Elizabeth B. ; Apprill, Amy
    Coral reef ecosystems are incredibly diverse marine biomes that rely on nutrient cycling by microorganisms to sustain high productivity in generally oligotrophic regions of the ocean. Understanding the composition of extracellular reef metabolites in seawater, the small organic molecules that serve as the currency for microorganisms, may provide insight into benthic-pelagic coupling as well as the complexity of nutrient cycling in coral reef ecosystems. Jardines de la Reina (JR), Cuba is an ideal environment to examine extracellular metabolites across protected and high-quality reefs. Here, we used liquid chromatography mass spectrometry (LC-MS) to quantify specific known metabolites of interest (targeted metabolomics approach) and to survey trends in metabolite feature composition (untargeted metabolomics approach) from surface and reef depth (6 – 14 m) seawater overlying nine forereef sites in JR. We found that untargeted metabolite feature composition was surprisingly similar between reef depth and surface seawater, corresponding with other biogeochemical and physicochemical measurements and suggesting that environmental conditions were largely homogenous across forereefs within JR. Additionally, we quantified 32 of 53 detected metabolites using the targeted approach, including amino acids, nucleosides, vitamins, and other metabolic intermediates. Two of the quantified metabolites, riboflavin and xanthosine, displayed interesting trends by depth. Riboflavin concentrations were higher in reef depth compared to surface seawater, suggesting that riboflavin may be produced by reef organisms at depth and degraded in the surface through photochemical oxidation. Xanthosine concentrations were significantly higher in surface reef seawater. 5′-methylthioadenosine (MTA) concentrations increased significantly within the central region of the archipelago, displaying biogeographic patterns that warrant further investigation. Here we lay the groundwork for future investigations of variations in metabolite composition across reefs, sources and sinks of reef metabolites, and changes in metabolites over environmental, temporal, and reef health gradients.
  • Preprint
    Dissolved organic carbon compounds in deep-sea hydrothermal vent fluids from the East Pacific Rise at 9°50′N
    ( 2018-08) Longnecker, Krista ; Sievert, Stefan M. ; Sylva, Sean P. ; Seewald, Jeffrey S. ; Kujawinski, Elizabeth B.
    Deep-sea hydrothermal vents are unique ecosystems that may release chemically distinct dissolved organic matter to the deep ocean. Here, we describe the composition and concentrations of polar dissolved organic compounds observed in low and high temperature hydrothermal vent fluids at 9°50’N on the East Pacific Rise. The concentration of dissolved organic carbon was 46 μM in the low temperature hydrothermal fluids and 14 μM in the high temperature hydrothermal fluids. In the low temperature vent fluids, quantifiable dissolved organic compounds were dominated by water-soluble vitamins and amino acids. Derivatives of benzoic acid and the organic sulfur compound 2,3-dihydroxypropane-1-sulfonate (DHPS) were also present in low and high temperature hydrothermal fluids. The low temperature vent fluids contain organic compounds that are central to biological processes, suggesting that they are a by-product of biological activity in the subseafloor. These compounds may fuel heterotrophic and other metabolic processes at deep-sea hydrothermal vents and beyond.
  • Preprint
    Release of ecologically relevant metabolites by the cyanobacterium Synechococcus elongatus CCMP 1631
    ( 2015-04-30) Fiore, Cara L. ; Longnecker, Krista ; Kido Soule, Melissa C. ; Kujawinski, Elizabeth B.
    Photoautotrophic plankton in the surface ocean release organic compounds that fuel secondary production by heterotrophic bacteria. Here we show that an abundant marine cyanobacterium, Synechococcus elongatus, contributes a variety of nitrogen-rich and sulfur-containing compounds to dissolved organic matter. A combination of targeted and untargeted metabolomics and genomic tools was used to characterize the intracellular and extracellular metabolites of S. elongatus. Aromatic compounds such as 4-hydroxybenzoic acid and phenylalanine, as well as nucleosides (e.g., thymidine, 5’-methylthioadenosine, xanthosine), the organosulfur compound 3-mercaptopropionate, and the plant auxin indole 3-acetic acid, were released by S. elongatus at multiple time points during its growth. Further, the amino acid kynurenine was found to accumulate in the media even though it was not present in the predicted metabolome of S. elongatus. This indicates that some metabolites, including those not predicted by an organism’s genome, are likely excreted into the environment as waste; however, these molecules may have broader ecological relevance if they are labile to nearby microbes. The compounds described herein provide excellent targets for quantitative analysis in field settings to assess the source and lability of dissolved organic matter in situ.
  • Preprint
    Deciphering ocean carbon in a changing world
    ( 2016-01-13) Moran, Mary Ann ; Kujawinski, Elizabeth B. ; Stubbins, Aron ; Fatland, Rob ; Aluwihare, Lihini I. ; Buchan, Alison ; Crump, Byron C. ; Dorrestein, Pieter C. ; Dyhrman, Sonya T. ; Hess, Nancy J. ; Howe, Bill ; Longnecker, Krista ; Medeiros, Patricia M. ; Niggemann, Jutta ; Obernosterer, Ingrid ; Repeta, Daniel J. ; Waldbauer, Jacob R.
    Dissolved organic matter (DOM) in the oceans is one of the largest pools of reduced carbon on Earth, comparable in size to the atmospheric CO2 reservoir. A vast number of compounds are present in DOM and they play important roles in all major element cycles, contribute to the storage of atmospheric CO2 in the ocean, support marine ecosystems, and facilitate interactions between organisms. At the heart of the DOM cycle lie molecular-level relationships between the individual compounds in DOM and the members of the ocean microbiome that produce and consume them. In the past, these connections have eluded clear definition because of the sheer numerical complexity of both DOM molecules and microorganisms. Emerging tools in analytical chemistry, microbiology and informatics are breaking down the barriers to a fuller appreciation of these connections. Here we highlight questions being addressed using recent methodological and technological developments in those fields and consider how these advances are transforming our understanding of some of the most important reactions of the marine carbon cycle.
  • Article
    Coherent patterns in bacterial growth, growth efficiency, and leucine metabolism along a northeastern Pacific inshore-offshore transect
    (Association for the Sciences of Limnology and Oceanography, 2011-01) del Giorgio, Paul A. ; Condon, Robert H. ; Bouvier, Thierry ; Longnecker, Krista ; Bouvier, Corinne ; Sherr, Evelyn B. ; Gasol, Josep M.
    We investigated the patterns in bacterial growth, production, respiration, growth efficiency (BGE), and bacterial leucine respiration and C-to-leucine yield (i.e., conversion factor [CF]) along a transect off the coast of Oregon. Plankton respiration along the transect averaged 1.15 ± 0.16 mg C L-1 h-1, peaking in the coastal upwelling region. The respiration in the filtered fraction, which was dominated by bacterial biomass, accounted for 79% of the total respiration. The different approaches that we used converged to an average BGE of 13% ± 1%, with peaks of over 20% in the more productive coastal areas and values declining to below 5% toward the oligotrophic gyre waters. There was overall coherence between the various aspects of bacterial C metabolism: communities with low BGE also tended to have low growth rates and high leucine-to-thymidine incorporation ratios. The patterns in BGE were mirrored at the single compound level, and in the most oligotrophic sites, bacteria tended to quickly respire a large fraction (20-75%) of the leucine that was taken up and had the lowest C-to-leucine yield, suggesting that the patterns in bulk BGE and growth also apply to individual substrates. Bacterial growth was a function of both C consumption and BGE; these two aspects of bacterial C metabolism do not necessarily covary, and they are regulated differently. The patterns in C consumption, growth, BGE, and leucine metabolism all reflect the basic physiological response of bacteria to energy limitation due to high maintenance costs associated with life in oligotrophy.
  • Preprint
    Effect of carbon addition and predation on acetate-assimilating bacterial cells in groundwater
    ( 2009-07-13) Longnecker, Krista ; Da Costa, Andreia ; Bhatia, Maya P. ; Kujawinski, Elizabeth B.
    Groundwater microbial community dynamics are poorly understood due to the challenges associated with accessing subsurface environments. In particular, microbial interactions and their impact on the subsurface carbon cycle remain unclear. In the present project, stable isotope probing with uniformly-labeled [13C]-acetate was used to identify metabolically-active and inactive bacterial populations based on their ability to assimilate acetate and/or its metabolites. Furthermore, we assessed whether substrate availability (bottom-up control) or grazing mortality (top-down control) played a greater role in shaping bacterial community composition by separately manipulating the organic carbon supply and the protozoan grazer population. A community fingerprinting technique, Terminal Restriction Fragment Length Polymorphism (T-RFLP), revealed that the bacterial community was not affected by changes in acetate availability but was significantly altered by the removal of protozoan grazers. In silico identification of terminal restriction fragments and 16S rDNA sequences from clone libraries revealed a bacterial community dominated by Proteobacteria, Firmicutes, and Bacteroidetes. Elucidation of the factors that structure the bacterial community will improve our understanding of the bacterial role in the carbon cycle of this important subterranean environment.