Review: Direct and indirect electrical stimulation of microbial metabolism.

All organisms require an electron donor and acceptor, frequently in chemical form, but an elegant alternative is to supply these via direct electrochemical means. Electricity has been used to stimulate microbial metabolism for over 50 years. Since the first report of oxygenating media using anodic oxygen generation from electrolysis in 1956, researchers have made use of applied power systems to supply energy for microbial respiratory processes from fermentations to anaerobic reduction of toxic pollutants. Bioelectrical reactors (BERs) have been utilized for culturing organisms, influencing metabolite production, and biotransformation of a wide array of compounds. Both enrichment and pure cultures have been cultivated in the presence of applied current, showcasing the applicative diversity of these systems. As the need for more environmentally conscious solutions to waste-treatment, remediation, and cultivation efforts increases, systems that supply energy to microorganisms without chemical amendment are becoming more attractive. Additionally, the essential flexibility of BERs offers an almost unlimited range of solutions for metabolic stimulation and downstream application.