Hydrothermal systems are important sources of dissolved Mn to the oceans. Upon oxidation of Mn(II), Mn(III,IV) oxides are deposited at the sea floor as crusts, nodules and sediments both near and far from the sources. Microbial activity has long been recognized as being important to the fate of Mn in these hydrothermal systems, yet we know very little about the organisms that catalyze Mn oxidation, the mechanisms by which Mn is oxidized or the physiological function that Mn oxidation serves. The overarching goals of this project are to reveal the organisms and mechanism(s) underlying Mn(II) oxidation, to evaluate whether hydrothermal Mn oxidizers may obtain energy from Mn oxidation, and test whether thermophilic Mn oxidizers exist. Specifically, the project will: 1) evaluate whether we can identify certain genomic sequences that correlate to the presence/concentration of Mn oxides (and hence Mn(II)- oxidizing bacteria) by comparing the metagenomes of ferromanganese (containing both Mn and Fe oxides) microbial mats with ferruginous (Fe oxide only) mats from Lau Basin and Loihi Seamount; 2) use peptide probes bound to magnetic particles for selectively binding and capturing Mn oxide particles and characterizing the particles using phylogenetic and functional gene (PCR and FISH) and transcriptomic analysis; 3) assess the main pathways of carbon fixation in ferromanganese microbial mats as compared to ferruginous mats as a possible indicator of Mn-based auto/mixotrophy using genomic approaches and substrate stimulated (e.g., addition of Mn(II)) CO2 fixation measurements and stable isotope probing (SIP) genomic analysis; and 4) isolate and characterize Mn(II)-oxidizing bacteria and determine whether thermophilic Mn oxidizers exist.
Intellectual merit The results of this research will increase our understanding of Mn(II) oxidation in hydrothermal sediments, identify microorganisms that are the environmentally relevant Mn oxidizers and begin to address the long standing question of whether Mn auto/mixotrophy exists using approaches not based on the biases associated with cultivation. Ultimately this information is critical to our understanding of biogeochemical cycles (Mn oxidation and Mn oxides impact many other elemental cycles, including carbon, sulfur, and heavy metals) and the natural attenuation of toxic metal and organic compounds; this may lead to improved technologies for environmental remediation. Because Mn oxides are believed to be an analog to the ancestral Mn centers in photosystem II, this research may also lend new insights into ancient biogeochemistry occurring before the Great Oxidation Event.
Broader impacts The project will provide support and training for one Ph.D. student and one postdoctoral researcher, and will contribute to the education of undergraduate and highly qualified high school students through independent research projects and mentorships. They will participate in a geoscience education program targeting the education of 6-12 grade Alaskan Native Americans. In addition, this project will contribute to a training program targeted to middle school teachers that highlights the connections between chemistry, biology, and geology in the environment. The results of the work will be broadly disseminated through presentations, publications, and the World Wide Web.