Facultative Nitrate Reduction by Electrode-Respiring Geobacter metallireducens Biofilms as a Competitive Reaction to Electrode Reduction in a Bioelectrochemical System

Abstract

Alternative metabolic options of exoelectrogenic biofilms in bioelectrochemical systems (BESs) are important not only to explain the fundamental ecology and performance of these systems but also to develop reliable integrated nutrient removal strategies in BESs, which potentially involve substrates or intermediates that support/induce those alternative metabolisms. This research focused on dissimilatory nitrate reduction as an alternative metabolism to dissimilatory anode reduction. Using the exoelectrogenic nitrate reducer Geobacter metallireducens, the critical conditions controlling those alternative metabolisms were investigated in two-chamber, potentiostatically controlled BESs at various anode potentials and biofilm thicknesses and challenged over a range of nitrate concentrations. Results showed that anode-reducing biofilms facultatively reduced nitrate at all tested anode potentials (-150 to +900 mV vs Standard Hydrogen Electrode) with a rapid metabolic shift. The critical nitrate concentration that triggered a significant decrease in BES performance was a function of anode biofilm thickness but not anode potential. This indicates that these alternative metabolisms were controlled by the availability of nitrate, which is a function of nitrate concentration in bulk solution and its diffusion into an anode-reducing biofilm. Coulombic recovery decreased as a function of nitrate dose due to electron-acceptor substrate competition, and nitrate-induced suspended biomass growth decreased the effluent quality.

Cross-biome comparison of microbial association networks

“…The predicted Nitrospirales–Geobacteraceae association might reflect a cross-feeding relationship, where Geobacteraceae species use nitrate generated by Nitrospirales members as electron acceptor. Although Geobacteraceae are better known as metal reducers, several Geobacteraceae species are able to grow on nitrate as the sole electron acceptor ( Kashefi et al, 2003 ; Kashima and Regan, 2015 ). Since Geobacteraceae species are anaerob and several members of Nitrospirales aerob, their interaction may take place indirectly via nitrate diffusing into deeper soil layers.…”

A Self-Sufficient Nitrate Groundwater Remediation System:Geobacter SulfurreducensMicrobial Fuel Cell Fed by Hydrogen from a Water Electrolyzer

“…Several species of Geobacter have been shown to reduce nitrates. [30][31][32] Geobacter sulfurreducens has been electrochemically studied as a biofilm 18,19,33 as well as immobilized on carbon electrodes by pectin, 20 where DET still occurred when the G. sulfurreducens were immobilized on the electrode without forming a biofilm.…”

Enhancing the Electricity Generation and Nitrate Removal of Microbial Fuel Cells With a Novel Denitrifying Exoelectrogenic Strain EB-1

“…To date, the effect of nitrate on electricity generation by exoelectrogens has not been determined. Few studies have reported that denitrifying exoelectrogens conduct denitrification as a facultative metabolism in bioelectrochemical systems (BESs) (Xing et al, 2010 ; Fu et al, 2013 ; Kashima and Regan, 2015 ). The power output of MFCs with Comamonas denitrificans (Xing et al, 2010 ) or Calditerrivibrio nitroreducens (Fu et al, 2013 ) was found to be decreased when nitrate was added to the anode chamber of MFCs, suggesting that the change in metabolic pathway affected the electricity performance negatively.…”

“…The power output of MFCs with Comamonas denitrificans (Xing et al, 2010 ) or Calditerrivibrio nitroreducens (Fu et al, 2013 ) was found to be decreased when nitrate was added to the anode chamber of MFCs, suggesting that the change in metabolic pathway affected the electricity performance negatively. Kashima and Regan ( 2015 ) subsequently reported that anodic denitrification and anode respiration shifted rapidly according to nitrate concentration in a BES inoculated with the anode-respiring bacterium Geobacter metallireducens , and that the current output of an MFC was strongly inhibited when the nitrate concentration was above the critical level (0–56 mg N L −1 ). The critical nitrate concentrations have a significant relationship with the biofilm protein concentrations of anode biofilms, without being appreciably impacted by the anode potential.…”