Photoreduction of Shewanella oneidensis extracellular cytochromes by organic chromophores and dye-sensitized TiO2

The transfer of photoenergized electrons from extracellular photosensitizers across a bacterial cell envelope to drive intracellular chemical transformations represents an attractive way to harness Nature’s catalytic machinery for solar to chemicals conversion. In Shewanella oneidensis MR-1 (MR-1) trans-outermembrane electron transfer is performed by the extracellular cytochromes MtrC and OmcA acting together with the outermembrane spanning porin:cytochrome complex (MtrAB). Here we demonstrate photoreduction of solutions of MtrC, OmcA and the MtrCAB complex by soluble photosensitizers, namely, eosin Y, fluorescein, proflavine, flavin adenine dinucleotide and two compounds secreted by MR-1, riboflavin and flavin mononucleotide. We show photoreduction of MtrC and OmcA adsorbed on Ru(II)-dye sensitized TiO₂ nanoparticles, and, that these protein coated particles perform photocatalytic reduction of solutions of MtrC, OmcA and MtrCAB. These findings provide a framework for informed development of strategies to use the outermembrane associated cytochromes of MR-1 for solar microbial synthesis in natural and engineered bacteria.