title: Kinetic, electrochemical, and microscopic characterization of the thermophilic, anode-respiring bacterium Thermincola ferriacetica.
abstract: 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.
authors.affiliation: Swette Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, P.O. Box 875701, Tempe, Arizona 85287, USA. prathap@asu.edu
authors.forename: Prathap
authors.initials: P
authors.lastname: Parameswaran
authors.forename: Tyson
authors.initials: T
authors.lastname: Bry
authors.forename: Sudeep C
authors.initials: SC
authors.lastname: Popat
authors.forename: Bradley G
authors.initials: BG
authors.lastname: Lusk
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Rittmann
authors.forename: César I
authors.initials: CI
authors.lastname: Torres
mesh_terms: D018441:Biofilms; D055664:Electrochemical Techniques; D004566:Electrodes; D006094:Gram-Positive Bacteria / Q000254:growth & development / Q000378:metabolism*; D007700:Kinetics; D008855:Microscopy, Electron, Scanning