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Project Progress

We have recently investigated the influence that vitamins have on the carbon isotopic fractionation from inorganic carbon to methane & biomass during methanogenesis (Vrentas et al., in prep.). The work was the basis for an undergraduate honors thesis by Jenny Vrentas. Jenny Vrentas was also a recipient of a NSF REU summer grant. Our basic research into the factors that control microbial fractionation is presently continuing with further studies by other students.

Over the last few years, we have also been working on nitrogen isotopic fractionation during nitrogen fixation in Anabaena, a cyanobacterium (Zerkle et al., submitted). It is widely noted that nitrogen fixation has little or no isotopic fractionation associated with it. However, our research has shown that a small fractionation is apparent, predictable, and reproducible as a function of Fe media concentration. This work may help explain negative nitrogen isotopes observed for biomass deposited in the Archean and during oceanic anoxic events.

Our lab has also published a pair of papers about deeply buried marine sediments. Our recent PNAS paper shows that deeply-buried marine Crenarchaeota are heterotrophic. The paper presents a case for dissimilatory methane oxidation in that environment (Biddle et al., 2006). This work also involved undergraduate students R. Anderson and T. Kelly.

Finally, we are continuing to look at growth conditions for important microbial groups in an effort to model the biological and geochemical attributes of ancient oceans. We are mostly investigating methanogens, phototrophic species, and microbes from seep sediment.