title: Electrochemical selection and characterization of a high current-generating Shewanella oneidensis mutant with altered cell-surface morphology and biofilm-related gene expression.
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.
authors.affiliation: School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji 192-0392, Tokyo, Japan. akouzuma@toyaku.ac.jp.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kouzuma
authors.forename: Hitomi
authors.initials: H
authors.lastname: Oba
authors.forename: Nozomi
authors.initials: N
authors.lastname: Tajima
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Hashimoto
authors.forename: Kazuya
authors.initials: K
authors.lastname: Watanabe
mesh_terms: D001674:Bioelectric Energy Sources; D018441:Biofilms / Q000254:growth & development*; D004251:DNA Transposable Elements; D004560:Electricity; D004734:Energy Metabolism; D020869:Gene Expression Profiling; D053858:Metabolic Networks and Pathways / Q000235:genetics; D016254:Mutagenesis, Insertional; D009154:Mutation; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D020592:Shewanella / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D013499:Surface Properties
chemical_list: D004251:DNA Transposable Elements; D011135:Polysaccharides, Bacterial