Results were published in the academic journal Biosensors & Bioelectronics and are the output of a collaboration work between LEQUIA and gEMM research groups from University of Girona and the Laboratory of Biotechnology of Institut National de Recherche Agronomique (INRA)
Can you imagine a technology able to remove pollutants from groundwater, treat wastewater, produce biofuels or develop biosensors? It already exists. It’s called bioelectrochemical systems (BES) and has arisen high interest among the international scientific community in the past few years. To understand how BES work, only two basic scientific concepts are needed: microorganisms – microscopic living organisms – and redox reactions – chemical reactions that lead to a change of oxidation state of chemicals by freeing and capturing electrons from an electrode. If redox reaction is catalysed by electroactive microorganisms, a bioelectrochemical reaction is taking place.
Some microorganisms can catalyse freeing of electrons while others catalyse their capture. A third group plays a role in both processes; depending on the applied conditions, these microorganisms catalyse oxidation (bioanode) or reduction (biocathode) reactions. This phenomenon is known as “bidirectional transfer of electrons” and, up to now, was still uncertain. Researchers from UdG groups LEQUIA and gEMM and LBE-INRA in France have conducted a joint research work that significantly contributes to a better understanding of the process.
The finding was published in the prestigious journal Biosensors & Bioelectronics by Narcís Pous, Anna Vilajeliu, Erika Fiset, Maria Dolors Balague, Sebastià Puig and Jesús Colprim (from LEQUIA); Lluís Bañeras (gEMM); and Alessandro Carmona and Nicolas Bernet (LBE-INRA). Results indicated that a biofilm predominantly composed of Geobacter sp. was able to oxidise acetate or reduce nitrate by using the same electron conduit. Hence, the study not only investigates the fundamentals of electron transfer conduits between electrode and electrically active microorganisms, but also allows thinking about developing a biosensor able to detect both acetate and nitrate – with relevant applications within the water sector.
To carry out this research, a mature anodic electroactive biofilm was developed from an activated sludge sample, acetate as electron donor and a poised electrode. Later, this biofilm was “switched” to biocathodic conditions by feeding it with a medium containing nitrates. The biofilm was predominantly composed by Geobacter sp. at both experimental conditions. The electrochemical characterisation indicated that both, acetate oxidation and nitrate reduction took place at a similar formal potential. Taken together, the results indicated that both processes could be catalysed by using the same electron conduit, and most likely by the same bacterial consortium. Hence, this study suggests that the electroactive bacteria within biofilms could use the same electron transfer conduit for catalysing anodic and cathodic reactions.
To sum up, this work is an important step towards both a better understanding of bioelectrochemical reactions and the possibility of exploiting one of its multiple potentials: the development of biosensors.
Narcís Pous, Alessandro A. Carmona-Martínez, Anna Vilajeliu-Pons, Erika Fiset, Lluis Bañeras, Eric Trably, M. Dolors Balaguer, Jesús Colprim, Nicolas Bernet and Sebastià Puig. Bidirectional microbial electron transfer: switching an acetate oxidizing biofilm to nitrate reducing conditions. Biosensors and Bioelectronics.