| A detailed picture of the chemical speciation of iron in seawater is required to comprehensively understand the marine iron cycle and its downstream effects on the cycles of other nutrient elements. Although much progress has been made in our understanding of iron-binding ligands in the marine environment, numerous questions remain as to their identity, structure, and biogeochemical sources and sinks. The recent proliferation of "omic" data from cultured organisms and environmental samples now allows us to address some of these chemical questions from a biologically informed perspective.;The research presented in this thesis examines some of the specific molecular mechanisms and underlying genetics that marine heterotrophic bacteria use to acquire iron from the unique chemical conditions of the marine environment. We first examined and reviewed the sources, transformations, and ultimate fate of heme and hemoproteins, iron containing molecules, in seawater. We used comparative genomics to characterize trace metal acquisition strategies in the marine Roseobacter and SAR11 clades, and we examined these uptake pathways in light of marine trace metal chemistry, microbial ecology, and genome evolution. We developed a genetic system for targeted mutagenesis and insertional inactivation of a predicted heme uptake TonB dependent outer membrane transporter in a model marine bacterial strain Ruegeria sp. TM1040. In a series of iron amended incubations from the California current ecosystem, we examined the heterotrophic bacterial assemblage composition using high throughput sequencing of bacterial marker genes in conjunction with chemical speciation and algal physiology. Finally, we examined putative iron uptake pathways in a metatranscriptome from natural marine phyto- and bacterioplankton communities in the southern California current and integrated patterns in the metatranscriptomic data with biogeochemical field data.;Our results have revealed genes responsible for trace metal metabolisms in marine heterotrophic bacteria and highlight heme uptake as a model heterotrophic iron assimilation pathway that is potentially important in particulate iron remineralization. In turn, we have provided additional insight to the chemical speciation of iron in seawater and have revealed potential molecular mechanisms by which heterotrophic bacteria shape the marine iron cycle. |
