Structure and Function of Bacterial Nanowires

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Bacterial nanowires are naturally occurring electrically conductive extensions produced by some anaerobic bacteria, including Geobacter sulfurreducens. They are primarily used to find electron acceptors in the environment so the bacteria can shed excess electrons produced during respiration, which is particularly relevant when oxygen is not available. These same bacterial strains can also form biofilms, and in these biofilms the nanowires link into a large network of nanowires. Networks can in some cases include nanowires from bacteria of a different species, which increases the likelihood of finding an electron acceptor. This network of natural electron-emitting bacterial nanowires has great potential for use as a microbial fuel cells, where we can gain electrical energy directly from the organisms. The goal of the proposed research is to elucidate the mechanism of electrical conduction through bacterial nanowires in biofilms. Our recent publication on a previously unknown cytochrome-based nanowire (OmcS) demonstrates how much is to be learned about the molecular mechanisms of conduction in protein filaments. Key questions we will address include: How many different types of conductive filaments exist? How is electricity conducted along a pilus? Is the regular array within the pilus disrupted when a neighbouring pilus makes contact, and if so, how is conductivity maintained? Do biofilms produce thick cables of conductive nanowires, or is the network delocalised? We will study nanowires from G. sulfurreducens as a representative system of bacterial nanowires using cryoelectron microscopy and single particle analysis for isolated nanowires, as well as focused ion beam (FIB)-milled biofilms and electron tomography for in situ studies of biofilms. This work will help us understand how bacteria work together in a network, and what limitations are inherent to the function of a biofilm. We expect that with some modifications to the structure of the nanowires, we can improve efficiency of electric conduction, leading to the design of an improved microbial fuel cell. Additionally, this research will help establish an important scientific method in Canada for the first time, in situ imaging of cells and cellular networks with molecular detail. The combination of FIB milling and cryo-electron tomography is proving to be very powerful, and its introduction into the Canadian research community is likely to have a strong impact and augment the work of many groups across the country.