Project description:Linking heterotrophic bacterioplankton community composition to the optical dynamics of dissolved organic matter in a large eutrophic Chinese lake
Project description:Measure changes in dissolved organic matter composition and resulting microbial decomposition rates in an experimentally warmed peatland.
Project description:<p>Metabolites, or the small organic molecules that are synthesized by cells during metabolism, comprise a complex and dynamic pool of carbon in the ocean. They are an essential form of information, linking genotype to phenotype at the individual, population and community levels of biological organization. Characterizing metabolite distributions inside microbial cells and dissolved in seawater is essential to understanding the controls on their production and fate, as well as their roles in shaping marine microbial food webs. Here, we apply a targeted metabolomics method to quantify particulate and dissolved distributions of a suite of biologically relevant metabolites including vitamins, amino acids, nucleic acids, osmolytes, and intermediates in biosynthetic pathways along a latitudinal transect in the western Atlantic Ocean. We find that, in the euphotic zone, most particulate or intracellular metabolites positively co-vary with the most abundant microbial taxa. In contrast, dissolved metabolites exhibited greater variability with differences in distribution between ocean regions. Although fewer particulate metabolites were detected below the euphotic zone, molecules identified in the deep ocean may be linked to preservation of organic matter or adaptive physiological strategies of deep-sea microbes. Based on the identified metabolite distributions, we propose relationships between certain metabolites and microbial populations, and find that dissolved metabolite distributions are not directly related to their particulate abundances.</p>
Project description:Coastal marine sediments, as locations of substantial fixed nitrogen loss, are very important to the nitrogen budget and to the primary productivity of the oceans. Coastal sediment systems are also highly dynamic and subject to periodic natural and anthropogenic organic substrate additions. The response to organic matter by the microbial community involved in nitrogen loss processes was evaluated using mesocosms of Chesapeake Bay sediments. Over the course of a 50-day incubation, rates of anammox and denitrification were measured weekly using 15N tracer incubations, and samples were collected for genetic analysis. Rates of both nitrogen loss processes and gene abundances associated with them corresponded loosely, probably because heterogeneities in sediments obscured a clear relationship. The rates of denitrification were stimulated more by the higher organic matter addition, and the fraction of nitrogen loss attributed to anammox slightly reduced. Furthermore, the large organic matter pulse drove a significant and rapid shift in the denitrifier community as determined using a nirS microarray, indicating the diversity of these organisms plays an essential role in responding to anthropogenic inputs. We also suggest that the proportion of nitrogen loss due to anammox in these coastal estuarine sediments may be underestimated due to temporal dynamics as well as from methodological artifacts related to conventional sediment slurry incubation approaches.
Project description:The fraction of dissolved dimethylsulfoniopropionate (DMSPd) converted by marine bacterioplankton into the climate-active gas dimethylsulfide (DMS) varies widely in the ocean, with the factors that determine this value still largely unknown. One current hypothesis is that the ratio of DMS formation:DMSP demethylation is determined by DMSP availability, with 'availability' in both an absolute sense (i.e., concentration in seawater) and in a relative sense (i.e., proportionally to other labile organic S compounds) being proposed as the critical factor. We investigated these models during an experimentally-induced phytoplankton bloom using an environmental microarray targeting DMSP-related gene expression in the Roseobacter group, a taxon of marine bacteria known to play an important role in the surface ocean sulfur cycle. The array consisted of 1,578 probes to 431 genes, including those previously linked to DMSP degradation as well as core genes common in sequenced Roseobacter genomes. The prevailing pattern of Roseobacter gene expression showed depletion of DMSP-related transcripts during the peak of the bloom, despite the fact that absolute concentrations and flux of DMSP-related compounds were increasing. A likely interpretation is that DMSPd was assimilated by Roseobacter populations in proportion to its relative abundance in the organic matter pool (the “relative sense” hypothesis), and that it is not taken up in preference to other sources of labile organic sulfur or carbon produced during the bloom. The relative investment of the Roseobacter community in DMSP demethylation did not predict the fractional conversion of DMSP to DMS, however, suggesting a complex regulatory process that may involve multiple fates of DMSPd.