A Hierarchically Modified Graphite Cathode with Au Nanoislands, Cysteamine, and Au Nanocolloids for Increased Electricity-Assisted Production of Isobutanol by Engineered Shewanella oneidensis MR-1

Abstract

It is necessary to understand the surface structural effects of electrodes on the bioalcohol productivity of Shewanella oneidensis MR-1, but this research area has not been deeply explored. Here, we report that the electricity-assisted isobutanol productivity of Shewanella oneidensis MR-1::pJL23 can be enhanced by sequentially modifying a graphite felt (GF) surface with Au nanoislands (Au), cysteamine (NH2), and Au nanoparticles (Au NPs). After bacteria were incubated for 50 h with the unmodified GF under various electrode potentials (vs Ag/AgCl), the bacterial isobutanol concentrations increased from 2.9 +/- 1 mg/L under no electricity supply to a maximum of 5.9 +/- 1 mg/L at -0.6 V. At this optimum electrode potential, the concentrations continued increasing to 9.1 +/- 1, 14 +/- 2, and 27 +/- 2 mg/L when the GF electrodes were modified with Au, NH2-Au, and Au NP-NH2-Au, respectively. We further studied how each surface structure affected the bacterial adsorptions, current profiles, and biofilms' electrochemical performances. In particular, these modifications induced the adsorption of elongated bacteria, with the amount dependent on the electrode structure. In the presence of electric supply, the amount of elongated bacteria further increased. We also found that the NH2-Au-GF and Au NP-NH2-Au-GF electrodes themselves could increase the concentrations to 11 +/- 0.3 and 12 +/- 2 mg/L, respectively, upon the bacterial incubation without electricity. Among the electrodes tested, the contribution of electricity to the bacterial isobutanol production was the greatest with the Au NP-NH2-Au-GF electrode. After 96 h of incubation, the concentration increased to 72 +/- 2 mg/L, which was 4.7 and 3.7 times the previously reported values obtained without and with electricity, respectively.