Lack of Periplasmic Non-heme Protein SorA Increases Shewanella decolorationis Current Generation.

Guannan Kong,Chunjie Zhu,Yonggang Yang,Da Song,Meiying Xu,Guoping Sun,Jun Guo,Fusheng Chen

doi:10.3389/fmicb.2020.00262

Abstract

Bacterial extracellular electron transport (EET) plays an important role in many natural and engineering processes. Some periplasmic non-heme redox proteins usually coexist with c-type cytochromes (CTCs) during the EET process. However, in contrast to CTCs, little is known about the roles of these non-heme redox proteins in EET. In this study, the transcriptome of Shewanella decolorationis S12 showed that the gene encoding a periplasmic sulfite dehydrogenase molybdenum-binding subunit SorA was significantly up-regulated during electrode respiration in microbial fuel cells (MFCs) compared with that during azo-dye reduction. The maximum current density of MFCs catalyzed by a mutant strain lacking SorA (ΔsorA) was 25% higher than that of wild strain S12 (20 vs. 16 μA/cm2). Both biofilm formation and the current generation of the anodic biofilms were increased by the disruption of sorA, which suggests that the existence of SorA in S. decolorationis S12 inhibits electrode respiration. In contrast, disruption of sorA had no effect on respiration by S. decolorationis S12 with oxygen, fumarate, azo dye, or ferric citrate as electron acceptors. This is the first report of the specific effect of a periplasmic non-heme redox protein on EET to electrode and provides novel information for enhancing bacterial current generation.

Highlights

Bacterial extracellular electron transport (EET) exists widely in natural environments
We found that the transcription levels of four genes of Shewanella decolorationis S12, SHD2782–SHD2785, were significantly up-regulated during EET to an electrode, compared that in anaerobic respiration with the azo-dye amaranth
In order to find proteins that are possibly specific to different extracellular electron acceptors, transcriptomes of S. decolorationis S12 respiring solid graphite electrode and soluble azo dye amaranth were compared

Summary

INTRODUCTION

Bacterial extracellular electron transport (EET) exists widely in natural environments. The mutant strain lacking either STC or FccA has a minor effect on the EET capability compared to wild strain S. oneidensis MR-1 (Bretschger et al, 2007; Schuetz et al, 2009; Firer-Sherwood et al, 2011), and a double-deletion mutant (lacking both STC and FccA) showed alternative pathways for EET with a lag-phase of several hours (Sturm et al, 2015), indicating that more redox proteins are involved in periplasmic electron transfer. Gene SHD2784 encodes a periplasmic sulfite dehydrogenase molybdenum-binding subunit SorA The disruption of this gene resulted in an increase of 25% in the maximum current density compared to the wild strain but had no effect on the reduction of azo dye and Fe (III) citrate.

MATERIALS AND METHODS

RESULTS AND DISCUSSION

DATA AVAILABILITY STATEMENT