Bidirectional microbial electron transfer: Switching an acetate oxidizing biofilm to nitrate reducing conditions.
Up to date a few electroactive bacteria embedded in biofilms are described to catalyze both anodic and cathodic reactions in bioelectrochemical systems (i.e. bidirectional electron transfer). How these bacteria transfer electrons to or from the electrode is still uncertain. In this study the extracellular electron transfer mechanism of bacteria within an electroactive biofilm was investigated by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). First, a mature anodic electroactive biofilm was developed from an activated sludge sample (inoculum), acetate as electron donor and a poised electrode (+397mV vs. SHE). Later, this biofilm was "switched" to biocathodic conditions by feeding it with a medium containing nitrates and poising the electrode at -303mV vs. SHE. The electrochemical characterization indicated that both, acetate oxidation and nitrate reduction took place at a similar formal potential of -175±05 and -175±34mV vs. SHE, respectively. The biofilm was predominantly composed by Geobacter sp. at both experimental conditions. Taken together, the results indicated that both processes could be catalyzed by using the same electron conduit, and most likely by the same bacterial consortium. Hence, this study suggests that electroactive bacteria within biofilms could use the same electron transfer conduit for catalyzing anodic and cathodic reactions.
LEQUiA, Institute of the Environment, University of Girona, C/ Maria Aurèlia Capmany, 69, Facultat de Ciències, E-17071 Girona, Spain.
Narcís
N
Pous
INRA, UR0050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, Narbonne F-11100, France.
Alessandro A
AA
Carmona-Martínez
LEQUiA, Institute of the Environment, University of Girona, C/ Maria Aurèlia Capmany, 69, Facultat de Ciències, E-17071 Girona, Spain.
Anna
A
Vilajeliu-Pons
LEQUiA, Institute of the Environment, University of Girona, C/ Maria Aurèlia Capmany, 69, Facultat de Ciències, E-17071 Girona, Spain.
Erika
E
Fiset
Molecular Microbial Ecology Group, Institute of Aquatic Ecology, University of Girona, Spain.
Lluis
L
Bañeras
INRA, UR0050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, Narbonne F-11100, France.
Eric
E
Trably
LEQUiA, Institute of the Environment, University of Girona, C/ Maria Aurèlia Capmany, 69, Facultat de Ciències, E-17071 Girona, Spain.
M Dolors
MD
Balaguer
LEQUiA, Institute of the Environment, University of Girona, C/ Maria Aurèlia Capmany, 69, Facultat de Ciències, E-17071 Girona, Spain.
Jesús
J
Colprim
INRA, UR0050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, Narbonne F-11100, France.
Nicolas
N
Bernet
LEQUiA, Institute of the Environment, University of Girona, C/ Maria Aurèlia Capmany, 69, Facultat de Ciències, E-17071 Girona, Spain. Electronic address: sebastia@lequia.udg.cat.
Sebastià
S
Puig
D000085:Acetates / Q000737:chemistry; D018441:Biofilms; D015374:Biosensing Techniques / Q000379:methods*; D019069:Cell Respiration; D004566:Electrodes; D004583:Electrons; D045302:Geobacter / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry; D010084:Oxidation-Reduction
D000085:Acetates; D009566:Nitrates
Bidirectional extracellular electron transfer; Bioanode; Biocathode; Bioelectrochemical systems; Electroactive biofilms