Collaborative Research: Biogeochemical drivers of interspecies electron transfer from iron reducers to methanogens

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Iron reduction and methanogenesis are two of the most common microbial reactions in nature. During iron reduction, microorganisms respire ferric iron, the form of iron in rust. During methanogenesis, microorganisms make methane, the primary component of natural gas and a potent greenhouse gas. Some iron reducers and methanogens, the microbes that drive the reactions, can cooperate with one another by sharing energy resources through interspecies electron transfer (IET). However, most predictive models assume that methanogens and iron reducers do not coexist, due to competition for energy sources, and only allow methane generation where ferric minerals have been depleted. Failure to account for both IET and competition may introduce error in process-based estimates of methane production. Moreover, environmental drivers of IET have not been identified, limiting the ability of models to predict how methane fluxes vary with environmental change. This study will create a new model for methanogenesis that links competitive and cooperative interactions. The model will improve the ability to predict methane generation and manage carbon budgets in natural and engineered systems including soils, aquifers, landfills, and wastewater treatment systems. The study will also provide training to undergraduate and graduate students and increase involvement of underrepresented groups in science through participation in the Kansas Louis Stokes Alliance for Minority Participation summer research program and summer outreach events for middle-school girls.Research goals of this study are to: 1) identify environmental drivers that push interactions of methanogens and iron reducers between competition and IET, 2) determine how changes in interactions between methanogens and iron reducers affect methane generation, and 3) evaluate the coupled role of enzyme properties and environmental chemistry in determining the nature of interactions. To achieve these goals, the study will integrate the results of bioreactor experiments with dynamic enzyme modeling. The bioreactor experiments will examine how interactions and methane production vary with key biogeochemical factors, including pH, ferric iron source, and the availability of electron donors and ferrous iron. The modeling analysis will consider enzyme kinetics and reaction energetics to simulate reactions at a subcellular/enzymatic level, with experiment results providing a basis for validation. Both competition and syntrophy between methanogens and iron reducers will be possible in the experiments and simulations, allowing the study to resolve how interactions and methane generation evolve with environmental chemistry. Moreover, study findings will create a roadmap for evaluating the environmental significance of IET between iron reducers and methanogens by defining an environmental context for this interaction. In doing so, study results will provide the tools needed to advance our understanding of ecological underpinnings of the global methane cycle.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.