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Open Access Research article

Electrochemical selection and characterization of a high current-generating Shewanella oneidensis mutant with altered cell-surface morphology and biofilm-related gene expression

Atsushi Kouzuma1*, Hitomi Oba1, Nozomi Tajima24, Kazuhito Hashimoto23 and Kazuya Watanabe1

Author Affiliations

1 School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji 192-0392, Tokyo, Japan

2 Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku 113-8656, Tokyo, Japan

3 Hashimoto Light Energy Conversion Project, ERATO/JST, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku 113-8656, Tokyo, Japan

4 Present address: Advanced Technologies Research Laboratories, Idemitsu Kosan, 1200 Kamiizumi, Sodegaura 299-0293, Chiba, Japan

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BMC Microbiology 2014, 14:190  doi:10.1186/1471-2180-14-190

Published: 16 July 2014

Abstract

Background

Shewanella oneidensis MR-1 exhibits extracellular electron transfer (EET) activity that is influenced by various cellular components, including outer-membrane cytochromes, cell-surface polysaccharides (CPS), and regulatory proteins. Here, a random transposon-insertion mutant library of S. oneidensis MR-1 was screened after extended cultivation in electrochemical cells (ECs) with a working electrode poised at +0.2 V (vs. Ag/AgCl) to isolate mutants that adapted to electrode-respiring conditions and identify as-yet-unknown EET-related factors.

Results

Several mutants isolated from the enrichment culture exhibited rough morphology and extraordinarily large colonies on agar plates compared to wild-type MR-1. One of the isolated mutants, designated strain EC-2, produced 90% higher electric current than wild-type MR-1 in ECs and was found to have a transposon inserted in the SO_1860 (uvrY) gene, which encodes a DNA-binding response regulator of the BarA/UvrY two-component regulatory system. However, an in-frame deletion mutant of SO_1860 (∆SO_1860) did not exhibit a similar level of current generation as that of EC-2, suggesting that the enhanced current-generating capability of EC-2 was not simply due to the disruption of SO_1860. In both EC-2 and ∆SO_1860, the transcription of genes related to CPS synthesis was decreased compared to wild-type MR-1, suggesting that CPS negatively affects current generation. In addition, transcriptome analyses revealed that a number of genes, including those involved in biofilm formation, were differentially expressed in EC-2 compared to those in ∆SO_1860.

Conclusions

The present results indicate that the altered expression of the genes related to CPS biosynthesis and biofilm formation is associated with the distinct morphotype and high current-generating capability of strain EC-2, suggesting an important role of these genes in determining the EET activity of S. oneidensis.

Keywords:
Extracellular electron transfer; Microbial fuel cell; Anode respiration; Bioelectrochemical systems