Geomicrobiology Laboratory

Work in my laboratory centers around a unique property of some microbes to control the biological iron cycle. We have discovered several new groups of both marine and freshwater bacteria that are capable of capturing enough energy to grow by oxidizing Fe(II) (ferrous iron) to Fe(III) (ferric iron). These lithoautotrophic, or chemosynthetic, bacteria are adapted to growing at very low oxygen levels, which is important, because at higher oxygen levels, the chemical oxidation of Fe(II) becomes so rapid it outcompetes biological oxidation. These Fe-oxidizing bacteria (FeOB) grow and are abundant in freshwater and brackish wetlands, water wells and distribution systems, hydrothermal vents in the ocean, marine sediments, and other marine environments where Fe(II) is present. They are economically important as nuisance agents in biofouling and related issues for water distribution systems, as well as their involvement in biocorrosion. They are beneficial in that they produce nanoparticulate, highly reactive iron oxides that are reactive with organic and inorganic pollutants, as well as being a source of bioavailable iron for iron-depleted ecosystems.

Highlights of work in my laboratory include pioneering efforts on the growth and isolation of novel Fe-oxidizing bacteria from both freshwater and marine environments. The discovery of the Zetaproteobacteria, a new class in the phylum Proteobacteria, that has a cosmopolitan distribution around the globe, but is restricted to marine environments with high concentrations of Fe(II). Comparative genetic analysis of pure cultures and environmental samples of FeOB that show marine and freshwater FeOB belong to very distinct lineages, sharing few genes in common, yet having convergent lifestyles in terms of niche preference, physiology, as well as unique morphotypes.

Together with colleagues from the US and around the world, we have discovered new new metabolic capabilities FeOB, including the ability to grow on hydrogen, in place of Fe(II), and to fix nitrogen. The unique filamentous mineral structures many FeOB produce as they grow are recognized in the fossil record, and we have shown that by understanding their colonial growth it is possible to interpret environmental conditions in ancient environments. Through comparative genomic and proteomic analysis, we have made significant progress in identifying possible genes involved in neutrophilic iron oxidation. This work is bringing us closer to understanding the mechanism of bacterial iron oxidation, which remains the most poorly understood major chemosynthetic metabolism on Earth. In more applied research, we have shown FeOB may initiate biocorrosion of steel that can lead to development of a biocorrosion microbiome.

Other recent discoveries include the finding that FeOB are abundant and the iron cycle is very active in the Arctic tundra; the discovery of a 10 meter tall 'iron tower' constructed by stalk-producing Zetaproteobacteria at a hydrothermal vent site in the Pacific, and ‘mineral-mediated motility’, a process whereby a filamentous iron-oxidizing bacterium propels itself via extrusion of a mineral encrusted sheath. The work in my lab is funded through the National Science Foundation, NASA, and the Office of Naval Research. We also have received significant sequencing support from the DOE's Joint Genome Institute.