Cytochrome nanowires under electron microscopy.

Microbial nanowires are appendages that Bacteria and Archaea use to transfer electrons to external surfaces, such as minerals, electrodes, or other microbes. While initial studies suggested that nanowires were modified pili, recent advancements in cryo-EM revealed that microbial nanowires are composed of multi-heme c-type cytochromes. In this review, we discuss the discovery of microbial nanowires, advancements that allowed elucidation of their near-atomic resolution cryo-EM structures, and the impact of heme arrangement on electron transfer. We also discuss how new structural information can be used to identify filaments in images from published literature. The structural insights gained from these studies provide a deeper understanding of the mechanisms underlying long-range electron transport in microbial nanowires and their potential applications in bioelectronics and energy-generating microbial fuel cells.