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Environ Sci Technol. 2013 May 7;47(9):4934-40. doi: 10.1021/es400321c. Epub 2013 Apr 18.

Kinetic, electrochemical, and microscopic characterization of the thermophilic, anode-respiring bacterium Thermincola ferriacetica.

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Swette Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, P.O. Box 875701, Tempe, Arizona 85287, USA.


Thermincola ferriacetica 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 T. ferriacetica and to perform a detailed microscopic and electrochemical characterization of the biofilm anode. T. ferriacetica 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 (EKA) of -0.127 V (vs) SHE. Confocal microscopy images revealed a thick layer of actively respiring cells of T. ferriacetica (~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 Geobacter 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 T. ferriacetica that can use a solid conductive matrix resulting in high current densities that are promising for MXC applications.

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