Generation of High Current Densities by Pure Cultures of Anode-Respiring Geoalkalibacter spp. under Alkaline and Saline Conditions in Microbial Electrochemical Cells

Abstract

Anode-respiring bacteria (ARB) generate electric current in microbial electrochemical cells (MXCs) by channeling electrons from the oxidation of organic substrates to an electrode. Production of high current densities by monocultures in MXCs has resulted almost exclusively from the activity of Geobacter sulfurreducens, a neutrophilic freshwater Fe(III)-reducing bacterium and the highest-current-producing member documented for the Geobacteraceae family of the Deltaproteobacteria. Here we report high current densities generated by haloalkaliphilic Geoalkalibacter spp., thus broadening the capability for high anode respiration rates by including other genera within the Geobacteraceae. In this study, acetate-fed pure cultures of two related Geoalkalibacter spp. produced current densities of 5.0 to 8.3 and 2.4 to 3.3 A m−2 under alkaline (pH 9.3) and saline (1.7% NaCl) conditions, respectively. Chronoamperometric studies of halophilic Glk. subterraneus DSM 23483 and alkaliphilic Glk. ferrihydriticus DSM 17813 suggested that cells performed long-range electron transfer through electrode-attached biofilms and not through soluble electron shuttles. Glk. ferrihydriticus also oxidized ethanol directly to produce current, with maximum current densities of 5.7 to 7.1 A m−2 and coulombic efficiencies of 84 to 95%. Cyclic voltammetry (CV) elicited a sigmoidal response with characteristic onset, midpoint, and saturation potentials, while CV performed in the absence of an electron donor suggested the involvement of redox molecules in the biofilm that were limited by diffusion. These results matched those previously reported for actively respiring Gb. sulfurreducens biofilms producing similar current densities (~5 to 9 A m−2).

The Family Desulfuromonadaceae

“…Optimizing the system components such as design, site, microbial balance, substrate, electrode composition, and temperature will lead to increases in the power generated (Ozkaya et al 2012;Ketep et al 2013;Holmes et al 2004c). The variable environmental conditions under which Desulfuromonadaceae isolates are able to grow offers the potential to apply microbial fuels cells to varying environments (Badalamenti et al 2013). In fact, the psychrotolerant Geopsychrobacter electrodiphilus was originally isolated from a marine sediment fuel cell.…”

High current density via direct electron transfer by the halophilic anode respiring bacterium Geoalkalibacter subterraneus

“…90 Furthermore, our results corroborate as well those of a recent publication by Miceli et al, 91 (2012) 32 showing Geoalkalibacter dominated biofilms derived from environmental anaerobic 92 samples (j max : 4.2 and 8.9 A/m 2 ). Similarly, Badalamenti et al (2013) 30 reported the 93 electrochemical performance of Glk. subterraneus grown on graphite rod electrodes under 94 lower saline conditions (1.7% NaCl).…”

Correlation of the Electrochemical Kinetics of High‐Salinity‐Tolerant Bioanodes with the Structure and Microbial Composition of the Biofilm

“…To our knowledge, this is the highest current density that has been reached in saline conditions by a bioanode formed from a pure culture. [24] A promising pathway has been recently opened up by using wild inoculum coming from a salt marsh. [25] The resulting microbial anodes have operated at electrolyte conductivities from 7.0 to 13.5 S m , which is around 1.5 times the conductivity of seawater; this represents a considerable advance with respect to the usual values of less than 2 S m À1 implemented in MESs.…”