Regulation of Gene Expression During Electron Acceptor Limitation and Bacterial Nanowire Formation in Shewanella oneidensis MR-1

In limiting oxygen as an electron acceptor, the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 rapidly forms nanowires, extensions of its outer membrane containing the cytochromes MtrC and OmcA needed for extracellular electron transfer. RNA-Seq analysis was employed to determine differential gene expression over time from cultures maintained in a chemostat and limited for oxygen. We identified 465 genes with decreased expression and 677 genes with increased expression. The coordinated increased expression of heme biosynthesis, cytochrome maturation, and transport pathways indicates that S. oneidensis MR-1 increases cytochrome production, including transcription of genes encoding MtrA, MtrC and OmcA, and properly positions these decaheme cytochromes in or near the outer membrane during nanowire formation. In contrast, the expression of the mtrA and mtrC homologs mtrF and mtrD either remain unaffected or decrease during nanowire formation. The ompW gene, encoding a small outer membrane porin, has 50-fold higher expression during oxygen limitation, and it is proposed that OmpW plays a role in cation transport to maintain electrical neutrality during electron transfer. The genes encoding the anaerobic respiration regulator CRP and the extracytoplasmic function sigma factor RpoE are among transcription factor genes with increased expression. RpoE could function by signaling the initial response to oxygen limitation. Our results show that RpoE activates transcription from promoters upstream of mtrC and omcA. The transcriptome and mutant analysis of S. oneidensis MR-1 nanowire production are consistent with independent regulatory mechanisms for extending the outer membrane into tubular structures and for ensuring the electron transfer function of the nanowires. Overall design: RNA-seq to identify temporal changes (5 timepoints) in gene expression in S. oneidensis MR-1 during nanowire formation in a chemostat.