GRAPHITE ELECTRODES AS ELECTRON ACCEPTOR FOR RESPIRATORY HYDROGEN OXIDATION BY Geobacter sulfurreducens.

FRITTAYON C.; ORDÓÑEZ, M.V.; GONZALEZ BLOTTA L.; SCHROTT GD

Los Cocos

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Asociación Civil de Microbiología General (SAMIGE)

Geobacter sulfurreducens is an anaerobic insoluble metal reducer (i.e Fe+3, Mn+4) proteobacteria. Its capacity to efficiently transport electrons from the respiratory chain to polarized electrodes made it the microorganism of choice to study and develop bioectrochemical processes based on bacterial electro-activity.G. sulfur reducens use acetate, formate or hydrogen as electron donors, a key role in syntrophic interaction, where these molecules are usual products of fermentationmetabolism.There is an increasing interest in studies working on syntrophic cultures to power biotechnological processes, where Geobacter metabolism allows removal of inhibitory end products of fermentation metabolism,being H2a central molecule in these combinations. A periplasmic oriented hydrogenase (i.e. Hyb), oxidase H2 and transfer electrons to menaquinone pools and thus enter into the respiratory chain. Nowadays, there are no studies on G. sulfurreducens biofilms grown on polarized electrodes using H2 as electron donor and electrodes as electron acceptors. The aims of this workpoint towards analyzing the possibility of that electric interactions and characterize the electrochemical variables that control the efficiency(i.e. electrode potential). Because it would allow the synergistic combination of metabolism plus bioelectric current generation. Initially, we cultivated biofilms anaerobically at 37ºC, in an electrochemical cell with two graphite electrodes as the only electron acceptor, sodium acetate as carbon and electron source, platinum wire as counter electrode and Ag/AgCl NaCl 3M as reference electrode. The working electrode was polarized at 0.2V against the reference electrode. N2/CO2 gas was continuously bubbled into the cell to prevent O2leaking and to complete bicarbonate buffer. Once the biofilm had grown, the medium was changed for one without acetate, allowing the current to decay. Then, to evaluate whether G. sulfurreducens can transfer electrons from hydrogen to the electrode, hydrogen was bubbled into the medium at saturation and the current was recorded. As a control, a clean graphite electrode was used under the same conditions. When the electrode wascovered by the biofilm, two orders of magnitude higher current were obtained than on the abioticelectrode, thus confirming that G. sulfurreducens is capable of transferring electrons from hydrogen oxidation to the electrode. Opening the door to using electrodes as electron acceptors for syntrophic cultures where G. sulfurreducens is needed to remove H2 to enhance fermentation metabolisms.