Electricity Generation by Shewanella decolorationis S12 without Cytochrome c.

Yonggang Yang,Yingli Lian,Xingjuan Chen,Guannan Kong,Wenzong Liu,Meiying Xu

doi:10.3389/fmicb.2017.01115

Abstract

Bacterial extracellular electron transfer (EET) plays a key role in various natural and engineering processes. Outer membrane c-type cytochromes (OMCs) are considered to be essential in bacterial EET. However, most bacteria do not have OMCs but have redox proteins other than OMCs in their extracellular polymeric substances of biofilms. We hypothesized that these extracellular non-cytochrome c proteins (ENCP) could contribute to EET, especially with the facilitation of electron mediators. This study compared the electrode respiring capacity of wild type Shewanella decolorationis S12 and an OMC-deficient mutant. Although the OMC-deficient mutant was incapable in direct electricity generation in normal cultivation, it regained electricity generation capacity (26% of the wide type) with the aid of extracellular electron mediator (riboflavin). Further bioelectrochemistry and X-ray photoelectron spectroscopy analysis suggested that the ENCP, such as proteins with Fe–S cluster, may participate in the falvin-mediated EET. The results highlighted an important and direct role of the ENCP, generated by either electricigens or other microbes, in natural microbial EET process with the facilitation of electron mediators.

Highlights

Bacterial extracellular electron transfer (EET) plays a crucial role in various natural biogeochemical cycles and engineering processes
The results suggested a significant role of Shewanella extracellular non-cytochrome c proteins (ENCP) in the mediated EET process
Several previous reports have indicated that flavin secretion capacity of Shewanella species would decreased in unfavorable growth conditions as lower flavin generation was observed in anaerobic or single electron acceptor condition than in aerobic or multiple electron acceptor condition, respectively

Summary

Introduction

Bacterial extracellular electron transfer (EET) plays a crucial role in various natural biogeochemical cycles and engineering processes. It can deliver electrons from intracellular substrate to extracellular solid acceptors such as mineral oxides, humics. The reported bacterial EET strategies can be generally divided into two types, that is, (i) direct electron transfer to extracellular electron acceptors via outer membrane c-type cytochromes (OMCs) or conductively proteinaceous nanowires and (ii) indirect electron transfer via naturally occurring or biogenic electron mediators. OMCs were considered to be essential for bacterial EET as the Shewanella Generate Electricity without Cytochrome c removal of OMCs could eliminate the electron transfer efficiency in both direct and indirect EET processes (Shi et al, 2009; Coursolle et al, 2010). A recent analysis of the prokaryotic proteomes suggested that most prokaryotes do not have OMCs

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