Biosensors and Bioelectronics 25 (2010) 1796–1802 Contents lists available at ScienceDirect Biosensors and Bioelectronics journal homepage: www.elsevier.com/locate/bios Characterization of an electro-active biocathode capable of dechlorinating trichloroethene and cis-dichloroethene to ethene Federico Aulenta a,∗ , Priscilla Reale a , Andrea Canosa a , Simona Rossetti b , Stefania Panero a , Mauro Majone a a Department of Chemistry, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy b Water Research Institute (IRSA-CNR), National Research Council, Area della Ricerca Roma 1, 00016 Monterotondo (RM), Italy article info Article history: Received 25 September 2009 Received in revised form 1 December 2009 Accepted 28 December 2009 Available online 4 January 2010 Keywords: Biocathode Bioremediation Extracellular electron transfer Trichloroethene Reductive dechlorination abstract In the presence of suitable electron donors, the industrial solvent trichloroethene (TCE) is reductively dechlorinated by anaerobic microorganisms, eventually to harmless ethene. In this study we investi- gated the use of a carbon paper electrode, polarized to -550 mV vs. standard hydrogen electrode (SHE), as direct electron donor for the mediator-less microbial reductive dechlorination of TCE to ethene. In potentiostatic batch assays, TCE was dechlorinated to predominantly cis-dichloroethene (cis-DCE) and lower amounts of vinyl chloride (VC) and ethene, at rates falling in the range 14.2–22.4 equiv./L d. When cis-DCE was spiked to the system, it was also dechlorinated, to VC and ethene, but at a much lower rate (1.5–1.7 equiv./L d). Scanning electron microscopy and FISH analyses revealed that the electrode was homogeneously colonized by active bacterial cells, each in direct contact with the electrode surface. Cyclic voltammetry tests revealed the presence, at the electrode interface, of formed redox active com- ponents possibly involved in the extracellular electron transfer processes, that were however detached by a vigorous magnetic stirring. Electrochemical impedance spectroscopy (EIS) tests revealed that polar- ization resistances of the electrode in the presence of microorganisms (ranging from 0.09 to 0.17 k/cm 2 ) were one-order of magnitude lower than those measured with abiotic electrodes (ranging from 1.4 to 1.8 k/cm 2 ). This confirmed that attached dechlorinating microorganisms significantly enhanced the kinetics of the electron transfer reactions. Thus, for the first time, the bio-electrochemical dechlorination of TCE to ethene is obtained without the apparent requirements for exogenous or self-produced redox mediators. Accordingly, this work further expands the range of metabolic reactions and microorgan- isms that can be stimulated by using solid-state electrodes, and has practical implications for the in situ bioremediation of groundwater contaminated by chlorinated solvents. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Several different microorganisms and mixed cultures have the capability of using insoluble and conductive materials as electron acceptors or donors in their energy metabolism (Rabaey et al., 2007). Microorganisms exhibiting this peculiarity are commonly referred to as “electro-active” (Logan, 2010). So far, the major interest in electro-active microorganisms has been in their appli- cation as biological catalysts of (waste) organic matter oxidation at the anode of microbial fuel cells (MFCs) (Logan et al., 2006; Rabaey and Verstraete, 2005) or microbial electrolysis cells (MECs) (Logan et al., 2008; Rozendal et al., 2006). Over the last years, MFCs and MECs have been explored extensively for their inno- vative features and environmental benefits (Logan et al., 2006). ∗ Corresponding author. Tel.: +39 06 49693224; fax: +39 06 06490631. E-mail address: Federico.Aulenta@uniroma1.it (F. Aulenta). Attempts have been made to shed light on the mechanisms of bacterial extracellular electron transfer. To date, the proposed mechanisms include: (i) direct electron transfer via redox com- ponents located on the outer surface of the microorganism (e.g., cytochromes, pilus-like appendages) and (ii) mediated electron transfer based on diffusible redox mediators (Schroder, 2007). More recently, bio-electrochemical systems, also named BES, have been proposed in applications outside the waste-to-energy sector, such as soil and groundwater bioremediation (Aulenta and Majone, 2009; Pham et al., 2009). In this context, electrodes have been pri- marily employed as electron donors for the reduction of oxidized contaminants in subsurface environments. The proof-of-concept of the bio-electrochemical reduction of oxidized contaminants with electrodes serving as electron donors has been shown for a vari- ety of compounds such as nitrate (Clauwaert et al., 2007), U(VI) (Gregory and Lovley, 2005), perchlorate (Shea et al., 2008), and chloroethenes (Aulenta et al., 2007, 2009b; Strycharz et al., 2008). The basic idea behind the use of electrodes and electrochemical 0956-5663/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2009.12.033