Electrochemistry of Biofilms

Biofilms are complex structures made of microorganisms, such as bacteria, embedded in a self-produced polymeric matrix called extracellular polymeric substances, attached together and to a surface. Biofilms are assumed to be the main life form of bacteria in the environment. With time, bacteria have developed for their survival various extracellular electron transfer pathways to exchange electrons with solid acceptors or donors. Biofilms made of these kinds of bacteria are called electroactive biofilms. They can be exploited to catalyze electrochemical reactions for energy production in microbial fuel cell, for molecule production in microbial electrosynthesis and environmental remediation in microbial electrocatalysis. Shewanella and Geobacter are two bacterial genera known to be electroactive. Shewanella oneidensis and Geobacter sulfurreducens are two bacterial species able to grow in biofilms that have been intensively studied as models in the field of microbial electrochemical technologies. Mechanisms of electron transfer in electroactive biofilms are really diverse, involving membrane cytochromes, conductive appendages, or self-produced electron carriers. To further increase this ability to transfer electrons between electroactive bacteria and electrodes, several strategies have been proposed: (1) to optimize electrode materials and surfaces, (2) to develop electroactive artificial biofilms and (3) to select or to modify genetically bacteria.