Abstract
Shewanella oneidensis exchanges electrons between cellular metabolism and external redox partners in a process that attracts much attention for production of green electricity (microbial fuel cells) and chemicals (microbial electrosynthesis). A critical component of this pathway is the outer membrane spanning MTR complex, a biomolecular wire formed of the MtrA, MtrB, and MtrC proteins. MtrA and MtrC are decaheme cytochromes that form a chain of close-packed hemes to define an electron transfer pathway of 185 Å. MtrA is wrapped inside MtrB for solubility across the outer membrane lipid bilayer; MtrC sits outside the cell for electron exchange with external redox partners. Here, we demonstrate tight and spontaneous in vitro association of MtrAB with separately purified MtrC. The resulting complex is comparable with the MTR complex naturally assembled by Shewanella in terms of both its structure and rates of electron transfer across a lipid bilayer. Our findings reveal the potential for building bespoke electron conduits where MtrAB combines with chemically modified MtrC, in this case, labeled with a Ru-dye that enables light-triggered electron injection into the MtrC heme chain.
Highlights
Dissimilatory metal-reducing bacteria (DMRB) are able to gain energy for growth by coupling the oxidation of organic compounds to the reduction of iron- and manganese-containing minerals
Examples include the remediation of water-borne organic “waste” molecules coupled to electricity production in microbial fuel cells, and the microbial electrosynthesis of valued chemicals from CO2 and N2 driven by electricity from renewable sources (Chiranjeevi and Patil, 2020)
These strategies rely on electron exchange between bacteria and electrodes
Summary
Dissimilatory metal-reducing bacteria (DMRB) are able to gain energy for growth by coupling the oxidation of organic compounds to the reduction of iron- and manganese-containing minerals. These terminal respiratory electron acceptors are insoluble. Periplasmic cytochromes STC and FccA transfer electrons from CymA to the outer membrane-associated MTR complex (Sturm et al, 2015). Electrons are transferred from the MTR complex to terminal respiratory acceptors either directly or via flavin mediators (von Canstein et al, 2008; Marsili et al, 2008). The MTR complex is proposed to transport protons across outer membranes as the rate-limiting event (Okamoto et al, 2017) during electron transfer from biofilms of S. oneidensis to electrodes
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