Biopolymer production in electroactive biofilms

Biofilms comprise of microorganisms encased in self-produced extracellular polymeric matrix, which provide resistance to antimicrobials and favors adhesion to nearly any surfaces. When biofilms grow onto electrodes, they are termed electroactive biofilm (EABs). The microorganisms in EABs are also known as electricigens. EABs are capable of extracellular electron transfer (EET) to and from solid acceptor, through direct or mediated mechanism. A thorough comprehension of the mechanism underlying EET is needed to develop productive EABs for bioprocesses. The EET mechanisms are investigated through a combination of electrochemical techniques (e.g., chronoamperometry and potentiostatic electrochemical impedance spectroscopy) and microscopy techniques. Following early studies on strong electricigens like Geobacter sp. and Shewanella sp., recent research has shown that most microorganisms exhibit weak electricigens activity under specific conditions, thus showing the possibility to develop novel bioelectrochemical industrial processes like electrofermentation (EF). EF can be applied to produce biopolymers in biofilms at higher yield and with different properties than conventional fermentation processes. Fluctuations in redox conditions in bioprocesses can alter the end-products, reduce their concentration, and lengthen the process time. EF enables rapid metabolic modulation of biosynthesis and allows control of redox imbalances in biofilm-based fermentation processes. In this presentation, I will give a brief introduction to electrochemical biofilm, with particular regards to weak electricigens. I will also show our recent work on electrofermentation to produce γ-PGA in Bacillus subtilis biofilms.