The Role of Shewanella oneidensis MR-1 Outer Surface Structures in Extracellular Electron Transfer

Authors

Rachida A. Bouhenni, Summa-Health System
Gary J. Vora, Naval Research Laboratory
Justin C. Biffinger, US Naval Research LaboratoryFollow
Sheetal Shirodkar, University of Wisconsin-Milwaukee
Ken Brockman, University of Wisconsin-Milwaukee
Ricky Ray, Naval Research Laboratory
Peter Wu, Naval Research Laboratory
Brandy J. Johnson, Naval Research LaboratoryFollow
Eulandria M. Biddle, University of Wisconsin-Milwaukee
Matthew J. Marshall, Pacific Northwest National Laboratory
Lisa A. Fitzgerald, Naval Research LaboratoryFollow
Brenda J. Little, Naval Research LaboratoryFollow
Jim K. Fredrickson, Naval Research LaboratoryFollow
Alexander S. Beliaev, Pacific Northwest National Laboratory
Bradley R. Ringeisen, Naval Research LaboratoryFollow
Daad A. Saffarini, University of Wisconsin-MilwaukeeFollow

Date of this Version

2010

Comments

Published in Electroanalysis (2010) 22, No. 7-8, 856 – 864; DOI: 10.1002/elan.200880006

Abstract

The ability of the metal reducer Shewanella oneidensis MR-1 to generate electricity in microbial fuel cells (MFCs) depends on the activity of a predicted type IV prepilin peptidase; PilD. Analysis of an S. oneidensis MR-1 pilD mutant indicated that it was deficient in pili production (Msh and type IV) and type II secretion (T2S). The requirement for T2S in metal reduction has been previously identified, but the role of pili remains largely unexplored. To define the role of type IV or Msh pili in electron transfer, mutants that lack one or both pilus biogenesis systems were generated and analyzed; a mutant that lacked flagella was also constructed and tested. All mutants were able to reduce insoluble Fe(III) and to generate current in MFCs, in contrast to the T2S mutant that is deficient in both processes. Our results show that loss of metal reduction in a PilD mutant is due to a T2S deficiency, and therefore the absence of c cytochromes from the outer surface of MR-1 cells, and not the loss of pili or flagella. Furthermore, MR-1 mutants deficient in type IV pili or flagella generated more current than the wild type, even though extracellular riboflavin levels were similar in all strains. This enhanced current generating ability is in contrast to a mutant that lacks the outer membrane c cytochromes, MtrC and OmcA. This mutant generated significantly less current than the wild type in an MFC and was unable to reduce Fe(III). These results indicated that although nanofilaments and soluble mediators may play a role in electron transfer, surface exposure of outer membrane c cytochromes was the determining factor in extracellular electron transfer in S. oneidensis MR-1.