From the Bottom up and Back: Nature-Inspired Electrochemical Platforms for Bioenergy and Bioremediation

In Nature, highly efficient and diverse consortia of microbes cycle carbon and other elements while generating energy for growth. Driving these reactions are organisms with the ability to extract electrons from the chemical substrates and transfer them to insoluble and soluble metals. One group in particular, Geobacter bacteria, can couple their metabolism to the reduction of insoluble minerals such as iron and manganese oxides. This natural process can be mimicked in electrochemical reactors, which provide a poised electrode as electron sink to drive the growth and catalytic activity of the bacteria. Whether alone or in partnership with other microbes, such Nature-inspired reactors show promise for the treatment of agricultural, industrial, and human wastes while generating added-value products and enabling water reuse. Geobacter cells are also able to reduce toxic metals such as uranium. To do so, they have evolved an electroactive cell envelope containing abundant metalloproteins. The electroactive envelope also serves as an anchor and charge injection system for conductive hair-like protein filaments or pili. The pilus filaments protrude from the cell, efficiently bind the uranium, and function as protein nanowires to reductively precipitate the radionuclide and mineralize it outside the cell. This effectively prevents the mobility of the uranium contaminants and protects the cells and other living components of the ecosystem, including humans, from exposure. Using genetic engineering approaches, we have mass-produced selected components of the Geobacter respiratory network and assembled them in vitro to develop nanostructure biomimetic interfaces for the bioremediation of uranium. From the nanoscale to the macroscale, the electroactivity of these microbes is used as inspiration to develop materials and devices for bioenergy and bioremediation application.