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, iron oxides that are highly 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. Our most recent work is focused on understand the role of FeOB in controlling iron cycling in the Arctic tundra, where we speculate it may play a critically impact the carbon cycle including methane production, and exert control on the availability of phosphorus. We are also pursuing interests in the use of biogenic iron oxides as nanomaterials with a variety of potential uses.

Together with colleagues from the US and around the world, we have discovered 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 produced by the growth of FeOB 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. 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.

Maine-eDNA. I initiated this project that has evolved into a large project for the state of Maine, and am Co-PI on a $20 million NSF EPSCoR Track 1 grant funding this work. All life is capable of producing a unique DNA signature or ‘fingerprint’. Environmental DNA (eDNA) is essentially the DNA signature of any particular sample. The source of the DNA may be entire organisms, as is the case with microbes, or genetic material left behind by larger organisms like fish, invertebrates, or seaweeds. With modern techniques we can analyze minute amounts of DNA in complex mixtures to determine who is there, and even estimate abundance. For Maine-eDNA, an interdisciplinary group of scientists from Bigelow, the University of Maine, the University of Southern Maine, Colby College, the Gulf of Maine Research Institute, Maine Maritime Academy, and Southern Maine Community College will conduct studies utilizing eDNA science to address several scientific hypotheses. Specific projects will track fish migrations, detect and track larval stages of shellfish and crustaceans, monitor, and potentially predict, harmful algal blooms, and track how marine species along Maine’s coast are responding to environmental change. Together this work will help us understand how eDNA can be put to use as tool for management of sustainable fisheries, monitoring harmful or invasive species, predicting how environmental change will impact ecosystems, and engaging the general public in an exciting new opportunity to do ocean forensics.