Selection of Shewanella oneidensis MR-1 gene-knockout mutants that adapt to an electrode-respiring condition

Abstract

Mutants of Shewanella oneidensis MR-1 that adapted to an electrode-respiring condition were selected from a random transposon-insertion mutant library to obtain active current-generating mutants and identify relevant cellular components. The mutants were selected in the presence of an electrode (poised at +0.2V vs. an Ag/ AgCl reference electrode) as the sole electron acceptor, and they were isolated on agar plates. Transposoninsertion sites in the isolated mutants were identified by inverse PCR coupled to sequence analyses. Southern blotting using a transposon probe was also performed to detect mutants that grew abundantly on the electrode. These analyses revealed that in many isolated mutants transposons were inserted in genes relevant to the synthesis of cell-surface structures, including SO-3350 (pilus synthesis), SO-3171 (polysaccharide synthesis), SO-3174 (polysaccharide synthesis), and SO-0165 (general secretion pathway). In microbial fuel cells, some of these (the SO-3350 and SO-4704 mutants) generated higher electrical outputs than wild-type MR-1, while the others generated lower outputs. The results suggest that cell-surface structures have a large influence on microbial current generation.