Extracellular Electron Transfer of S. oneidensis MR 1: Fundamentals and Applications

Bioelectrochemical systems (BESs) offer attractive applications in environmental remediation, energy harvesting, sensing, and organic and inorganic chemical synthesis. Fundamental studies of BESs not only hold promise for better performance of BES applications but are also crucial for the understanding of processes in nature. These processes, mainly extracellular electron transfer (EET), alter and affect the biogeochemical cycles.
In this Ph.D. project, S. oneidensis MR-1 (MR-1), an extensively investigated electrochemically active bacterium (EAB), was chosen as a tool to probe the EET process, which is essential in BESs. An opposite process of the outward EET, inward EET of MR-1 was here discovered. In inward EET, MR-1 catalyzes specific electrooxidation of redox molecules and exhibits asymmetric cyclic voltammograms. The electrocatalysis is highly selective and efficient. Among twelve redox molecules studied, only molecules with high midpoint potential and negative electrostatic charge(s) show electrocatalysis. [Fe(CN)6]4- as a representative of these molecules was chosen for deeper studies.
Further studies reveal that the formation of Pd nanoparticles (NPs) blocked the electrocatalysis systematically. On the other hand, the depletion of MtrC and OmcA, two crucial cytochromes c for outward EET, and inactivation of MR-1 did not deprive the ability of MR-1 of inward EET. A model coupling the oxidation of [Fe(CN)6]4- and [Fe(CN)6]4-/3- as catalytic mediator is hence proposed.
MR-1 was also applied in the biosynthesis of nanomaterials. Biosynthesis of nanomaterials can undertake a dual-task: bioremediation and biorecovery. To bridge the current gaps between laboratory investigations and practical applications, the effects of Cu(II) and different media were explored. The pre-culture in Cu(II) showed no critical inhibition of the bioremediation of Pd(II), and relatively high removal efficiency was achieved. However, pre-incubation of Cu(II) apparently altered the morphologies of the recovered nanomaterials. Inclusion of phosphate can increase the recovery efficiency of Pd(II), but only with limited enhancement.