Metabolites of Surface Ocean Carbon Cycle
Bacterioplankton control the flux of dissolved organic carbon (DOC) into the microbial food web and influence the release of inorganic carbon to atmospheric and offshore reservoirs. The specific metabolites that sustain the growth of bacteria and serve as links between microbial autotrophs and heterotrophs in the ocean are largely unknown, however, due largely to half-lives on the order of minutes and concentrations in the picomolar range. Our research is identifying the labile molecules produced by marine phytoplankton, and measuring the rates and controls on their processing by bacterial communities.
Bacterial Roles in Organic Sulfur Cycling
DMSP (dimethylsulfoniopropionate) is a dissolved organic sulfur (DOS) metabolite released into seawater by marine phytoplankton where it is readily taken up and transformed by bacteria. One of its bacterial degradation products, dimethylsulfide (DMS), is the predominant natural source of sulfur to the atmosphere. Recently, we have found that DMSP is not the only important sulfur-containing phytoplankton metabolite supporting bacterial heterotrophy: a number of sulfonate compounds are also being synthesized by marine phytoplankton and rapidly utilized by marine bacteria. Our research focuses on identifying bacterial genes for DOS transformation through molecular biology, genomic, and functional genomic studies with model marine bacteria; investigating organic sulfur-mediated interactions between bacteria and phytoplankton in laboratory systems; and conducting field research with coastal bacterial and phytoplankton communities to capture real-time DOS gene expression and flux in the ocean.
By sequencing mRNAs retrieved directly from microbial communities in seawater, we can ‘eavesdrop’ on the activities of natural bacterial communities. This gene expression data provides a direct link between the genetic potential of a community and their biogeochemical activities. We are applying this approach to understand diel, seasonal, and interannual changes in activities of bacteria in coastal and open ocean environments.
Roseobacter Model Organism System Development
Almost 60 genome sequences are available for cultured members of the marine Roseobacter lineage. Since this group is a dominant member of most coastal seawater communities, the sequenced strains provide a powerful system to understanding the activities of their wild relatives. We have been developing genetic systems, functional genomics approaches, culturing protocols, and bioinformatics resources (www.roseobase.org) to facilitate discoveries of the ecological and biogeochemical roles of these ubiquitous marine bacterioplankton.