Identification of an ECF sigma factor that facilitates electroactive biofilm formation by Shewanella oneidensis MR-1: Experiment 1

Shewanella oneidensis MR-1 was grown on electrodes in electrochemical flow cells (EFC), and the transcriptome profiles of electrode-attached MR-1 cells were compared under electrolyte-flow and static (non-flow) conditions. The results revealed that the SO_3096 gene encoding a putative extracytoplasmic function (ECF) sigma factor, as well as genes related to cyclic-di-guanosine monophosphate and flagella synthesis (e.g., SO_3556 and flrC) and c-type cytochrome maturation (dsbD), was significantly up-regulated under the electrolyte-flow condition. Compared to wild-type MR-1 (WT), a deletion mutant of SO_3096 (∆SO_3096) showed an impaired biofilm formation and a decreased current generation in EFC, suggesting that the ECF sigma factor encoded by this gene is involved in the regulation of biofilm formation and current generation under electrolyte-flow conditions. We also compared the transcriptome profiles of WT and ∆SO_3096 grown in EFC, confirming that many genes up-regulated under the electrolyte-flow condition, including dsbD, were down-regulated in ∆SO_3096. Transcription analysis using lacZ as a reporter gene showed that the promoter of dsbD is activated in the presence of SO_3096. Measurement of current generation by a dsbD-deletion mutant revealed that this gene is essential for electron transfer to electrodes. These results suggest that the SO_3096 protein serves as an ECF sigma factor that regulates cellular functions related to electroactive biofilm formation under electrolyte-flow conditions. AFP-expressing MR-1 grown under a non-flow condition. AFP-expressing MR-1 grown under a flow condition. Total 8 samples, 4 biological replicates for each sample