Kinetic, Electrochemical, and Microscopic Characterization of the Thermophilic, Anode-Respiring Bacterium <i>Thermincola ferriacetica</i>

<i>Thermincola ferriacetica</i> is a recently isolated thermophilic, dissimilatory Fe­(III)-reducing, Gram-positive bacterium with capability to generate electrical current via anode respiration. Our goals were to determine the maximum rates of anode respiration by <i>T. ferriacetica</i> and to perform a detailed microscopic and electrochemical characterization of the biofilm anode. <i>T. ferriacetica</i> DSM 14005 was grown at 60 °C on graphite-rod anodes poised at −0.06 V (vs) SHE in duplicate microbial electrolysis cells (MECs). The cultures grew rapidly until they achieved a sustained current density of 7–8 A m^–2 with only 10 mM bicarbonate buffer and an average Coulombic Efficiency (CE) of 93%. Cyclic voltammetry performed at maximum current density revealed a Nernst–Monod response with a half saturation potential (<i>E</i>_KA) of −0.127 V (vs) SHE. Confocal microscopy images revealed a thick layer of actively respiring cells of <i>T. ferriacetica</i> (∼38 μm), which is the first documentation for a gram positive anode respiring bacterium (ARB). Scanning electron microscopy showed a well-developed biofilm with a very dense network of extracellular appendages similar to <i>Geobacter</i> biofilms. The high current densities, a thick biofilm (∼38 μm) with multiple layers of active cells, and Nernst–Monod behavior support extracellular electron transfer (EET) through a solid conductive matrix – the first such observation for Gram-positive bacteria. Operating with a controlled anode potential enabled us to grow <i>T. ferriacetica</i> that can use a solid conductive matrix resulting in high current densities that are promising for MXC applications

Kinetic, Electrochemical, and Microscopic Characterization of the Thermophilic, Anode-Respiring Bacterium <i>Thermincola ferriacetica</i>

<i>Thermincola ferriacetica</i> is a recently isolated thermophilic, dissimilatory Fe­(III)-reducing, Gram-positive bacterium with capability to generate electrical current via anode respiration. Our goals were to determine the maximum rates of anode respiration by <i>T. ferriacetica</i> and to perform a detailed microscopic and electrochemical characterization of the biofilm anode. <i>T. ferriacetica</i> DSM 14005 was grown at 60 °C on graphite-rod anodes poised at −0.06 V (vs) SHE in duplicate microbial electrolysis cells (MECs). The cultures grew rapidly until they achieved a sustained current density of 7–8 A m^–2 with only 10 mM bicarbonate buffer and an average Coulombic Efficiency (CE) of 93%. Cyclic voltammetry performed at maximum current density revealed a Nernst–Monod response with a half saturation potential (<i>E</i>_KA) of −0.127 V (vs) SHE. Confocal microscopy images revealed a thick layer of actively respiring cells of <i>T. ferriacetica</i> (∼38 μm), which is the first documentation for a gram positive anode respiring bacterium (ARB). Scanning electron microscopy showed a well-developed biofilm with a very dense network of extracellular appendages similar to <i>Geobacter</i> biofilms. The high current densities, a thick biofilm (∼38 μm) with multiple layers of active cells, and Nernst–Monod behavior support extracellular electron transfer (EET) through a solid conductive matrix – the first such observation for Gram-positive bacteria. Operating with a controlled anode potential enabled us to grow <i>T. ferriacetica</i> that can use a solid conductive matrix resulting in high current densities that are promising for MXC applications