A Microenvironment for Shewanella oneidensis MR-1 Exists within Graphite Felt Electrodes

Abstract

Listen

Translate article

Shewanella oneidensis MR-1 employs various methods of Extracellular Electron Transport (EET) to insoluble terminal electron acceptors, including graphite felt anodes of BioElectrochemical Systems (BESs). Fibers in the felt form a three dimensional meshwork within which microbes can form biofilms, as well as occupy the interstitial spaces as planktonic cells. Our results indicate that these interstices generated by the meshwork create a novel microenvironment where planktonic cells grow to higher density under certain conditions. When incubated anaerobically with 18 mM lactate and 30 mM fumarate, planktonic cell counts within the electrodes are ∼10-fold higher than bulk planktonic cell counts; a phenomenon we termed the “interstitial felt effect”. Upon lowering both lactate and fumarate concentrations 10-fold, while bulk planktonic cell counts are stable, the interstitial felt effect disappears. This effect reappears when lactate and fumarate concentrations are lowered another 10-fold. Cyclic voltammetry experiments did not reveal any modification of the graphite fibers within the electrodes. A mutant strain lacking the primary flavin transporter gene, bfe, also expresses the interstitial felt effect. The interstitial planktonic microenvironment of electrically inert polyurethane sponge did not demonstrate this phenomenon. This study provides new insights into interactions of microbes with electrode materials that may help improve overall BES performance.