Hydrothermal vents are a globally significant source of dissolved manganese (II), an essential micronutrient for organisms and a valuable tracer of hydrothermal activity. In oxic waters such as hydrothermal plumes, soluble Mn(II) is eventually oxidized to Mn(III/IV) oxides. These "scavengers of the sea" (Goldberg 1954) are highly reactive minerals that are known to sequester a variety of metals and participate in redox reactions with a wide range of inorganic and organic compounds, thus playing an important role in marine geochemistry. Bacteria catalyze the oxidation of Mn(II) to Mn(III/IV) at hydrothermal vents and other environments and are thus thought to be responsible for the formation of natural Mn(III/IV) oxide minerals. Although many studies have shown that bacteria are responsible for the rapid Mn oxidation rates observed in the environment, relatively little is known about the organisms involved, the mechanism(s) and products of Mn biomineralization, and the biological function of Mn(II) oxidation.
In this study, researchers from the University of California- San Diego Scripps Institute of Oceanography will identify the bacterial community responsible for Mn oxidation in Guaymas Basin (GB) vent plumes, determine the molecular mechanism and products of Mn oxide biomineralization, and elucidate the role of ribulose-1,5-bisphosphate carboxylase (rubisco) genes recently found in Mn-oxidizing bacteria isolated near hydrothermal vents. The mechanism(s) and products of Mn oxidation in GB hydrothermal plumes will be investigated utilizing new insights into the molecular biology of bacterial oxidation and advanced spectroscopic techniques. Molecular probes will be designed to analyze the environmental diversity and distribution of genes involved in Mn oxidation. Mn oxidation rates will be measured in GB plume waters under a range of conditions designed to test our hypotheses concerning specific molecular mechanisms of Mn oxidation. X-ray absorption spectroscopy and synchrotron radiation X-ray diffraction will be used to characterize natural Mn oxides and reaction intermediates and products produced by Mn-oxidizing isolates. To investigate the function of bacterial Mn oxidation, the scientists will examine the role of genes involved in autotrophic carbon fixation (rubisco) in Mn oxidizing bacteria recently isolated from deep-sea hydrothermal vents. To detect expression of these genes both laboratory (physiology) experiments on Mn-oxidizing bacterial isolates and fieldwork will be performed.
