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Significance Recent findings from in vivo fluorescence and immunolabeling measurements hinted at the possible role of outer membrane (OM) extensions as Shewanella oneidensis MR-1 nanowires. However, a detailed understanding of the architecture and electron transport mechanism along OM extensions was lacking. In this work, we report a unique setup for correlative light and electron microscopy of Shewanella OM extensions and demonstrate that they are chains of interconnected outer membrane vesicles with densities, consistent with periplasmic and OM cytochromes, distributed along their length. We propose, based on the packing density of cytochromes measured from electron cryotomograms, that the electron transport mechanism involves a combination of direct electron hopping and diffusion of electron carriers.
Subramanian et al. (Mon,) studied this question.