Electroactive bacteria are living micro-organisms that are able to directly connect their respiratory metabolism to their extracellular environment by transferring electrons across biological membranes to, or from solids like metal oxides or electrodes. These bacteria are organized at conducting surfaces as biofilms and can indeed shuttle electrons via periplasmic and membrane proteins to/from electrodes. Hence, electroactive bacteria represent living, stable, self-replicating, and low-cost electrode catalysts. This unique property leads to potential “green” biotechnology applications such as microbial fuel cells, microbial electrosynthesis cells, wastewater treatment, desalination and biosensors. In order to permit the advent of these promising microbial electrochemical technologies it is crucial to progress toward the fundamental knowledge of these electroactive biofilms. Electroactive microorganisms such as Gram negative Geobacter sulfurreducens directly connect and transfer electrons to anodes via outer-membrane c-type cytochrome redox proteins as ultimate redox relays. In the absence of an organic substrate like acetate, at least four redox proteins may be detected electrochemically in the biofilm, while in the presence of an organic substrate extracellular electron release from bacterial catabolism is easily followed by recording a catalytic anodic current. The anolyte then becomes more acidic consistent with the oxidation of the organic substrate to carbon dioxide concomitantly with proton release. Acidification of the anolyte, of the biofilm and/or of the biofilm/electrode interface compromises the performance and viability of the catalytic biofilms. In fact, the extracellular electron transfer may be coupled to proton transfer in outer-membrane c-type cytochromes or, alternatively, non-redox proton transport proteins may be responsible for the acidification of the anolyte. Although extracellular electron and proton transfers are known to occur in electroactive bacteria, the fundamental understanding of these processes is still in its infancy and precludes the optimization of microbial electrochemical technologies.
The overall objective of MELBA is to develop an efficient and versatile electrochemical platform for probing electroactive bacteria membrane proteins incorporated in artificial lipid deposits supported on modified carbon electrode. In a first approach, the electrodes are modified with pH-responsive electrophores such as quinone units and then covered by lipid layers or deposits creating an artificial supported lipid membrane in which membrane proteins are incorporated and electrochemically probed. Indeed, the intrinsic electroactivity of the protein (if any) can be probed directly with the lipid modified electrode and possible proton transport occurring across the lipid layer by the membrane protein can in principle be detected with the grafted pH-responsive redox probe.
Concerning the career objectives of the fellow, the goal of holding a permanent academic position in France has been reached because the experienced researcher will be hired as an assistant professor at the University of Nantes (France) on September 2019.
