title: Redox and pH microenvironments within Shewanella oneidensis MR-1 biofilms reveal an electron transfer mechanism.
abstract: The goal of this research was to quantify the variations in redox potential and pH in Shewanella oneidensis MR-1 biofilms respiring on electrodes. We grew S. oneidensis MR-1 on a graphite electrode, which was used to accept electrons for microbial respiration. We modified well-known redox and pH microelectrodes with a built-in reference electrode so that they could operate near polarized surfaces and quantified the redox potential and pH profiles in these biofilms. In addition, we used a ferri-/ferrocyanide redox system in which electrons were only transferred by mediated electron transfer to explain the observed redox potential profiles in biofilms. We found that regardless of the polarization potential of the biofilm electrode, the redox potential decreased toward the bottom of the biofilm. In a fully redox-mediated control system (ferri-/ferrocyanide redox system), the redox potential increased toward the bottom when the electrode was the electron acceptor. The opposite behavior of redox profiles in biofilms and the redox-controlled system is explained by S. oneidensis MR-1 biofilms not being redox-controlled when they respire on electrodes. The lack of a significant variation in pH implies that there is no proton transfer limitation in S. oneidensis MR-1 biofilms and that redox potential profiles are not caused by pH.
authors.affiliation: The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington 99164, United States.
authors.forename: Jerome T
authors.initials: JT
authors.lastname: Babauta
authors.forename: Hung Duc
authors.initials: HD
authors.lastname: Nguyen
authors.forename: Haluk
authors.initials: H
authors.lastname: Beyenal
mesh_terms: D018441:Biofilms / Q000187:drug effects; D019149:Bioreactors / Q000382:microbiology; D003470:Culture Media / Q000494:pharmacology; D004583:Electrons; D005292:Ferricyanides / Q000378:metabolism; D005295:Ferrocyanides / Q000378:metabolism; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D008839:Microelectrodes; D010084:Oxidation-Reduction / Q000187:drug effects; D020592:Shewanella / Q000187:drug effects / Q000502:physiology*; D013816:Thermodynamics
chemical_list: D003470:Culture Media; D005292:Ferricyanides; D005295:Ferrocyanides; C007931:hexacyanoferrate III; C020354:hexacyanoferrate II