Environmental Engineering & Earth Sciences Seminar

"Bioelectrochemical Systems as Experimental Platforms for Studying Microbial Physiology: nitrate and electrode utilization by Geobacter metallireducens biofilms" presented by:  Dr. John Regan, Professor of Environmental Engineering, Pennsylvania State University.

Extracellular electron transport is important in many contexts, including natural settings and ecosystems as well as bioelectrochemical systems (BESs), which involve microbe-mediated reactions involving anode reduction and/or cathode oxidation. Determining the parameters affecting extracellular electron transfers is critical for understanding microbial communities with interspecies electron transfers and environments with redox reactions involving extracellular substrates, and to the development and operation of stable BESs. This presentation will emphasize the use of BESs to study extracellular electron transfers, specifically involving electrode-mediated reactions of the model exoelectrogen and exoelectrotroph Geobacter metallireducens. The metabolic shifts in anodically grown G. metallireducens biofilms were investigated over a range of electrode potentials and in the presence of alternative electron acceptors and donors. The results showed G. metallireducens preferentially reduced nitrate over an anode at all tested anode potentials, even when the anode was the thermodynamically favorable electron acceptor. G. metallireducens biofilms also demonstrated a quick and reversible shift between anode reduction and cathode oxidation as a function of electrode potential and availability of nitrate and acetate. Cathodic electrode oxidation was coupled with nitrate reduction by metabolically active biofilms, with a large cathodic current of ~ 3.68 A/m2. The metabolic shift from anode reduction to nitrate reduction took place quicker than the shift from ferric reduction to nitrate reduction. The presence of specific in-vitro nitrate-reducing enzyme activity in the anode-reducing biofilm cells in the absence of nitrate was thought to enable such a rapid metabolic shift to start nitrate reduction. Cyclic voltammetry and other analytical electrochemistry techniques provide a real-time and minimally invasive platform for investigating such extracellular redox reactions over a range of potentiostatically controlled conditions.

Jay Regan is a Professor of Environmental Engineering at Penn State University.  He worked for five years in environmental consulting at Warzyn and Montgomery Watson, and then earned his Ph.D. from the University of Wisconsin-Madison working with Daniel Noguera. He has been at Penn State since 2002. His research interests are in environmental biotechnology, focusing on using microbes to convert wastes into various energy carriers and products in bioelectrochemical systems and anaerobic digesters, and also bacterial transformations of nitrogen and phosphorus in both engineered and natural ecosystems. This coming fall he will be on sabbatical at Universidad Politécnica de Madrid working on nitrogen transformations in agricultural soils.

This seminar is hosted by the Department of Civil & Environmental Engineering & Earth Sciences at the University of Notre Dame.