UCLA

Exoelectrogenic bacteria can transfer the electrons out of the cell body through the extracellular electron transfer (EET) process after consuming various organic matters, which attracts increasing attentions in both academia and industrial communities. In this dissertation, I will focus on a typical exoelectrogenic bacterium Shewanella and its cooperating with inorganic materials such as nano-devices and nanoparticles. In the Shewanella-nano-devices hybrids, the current output features and cell density can be both in-situ monitored and studied. Take a further step, by anchoring the metal nanoparticles into the Shewanella membrane structures and bulk biofilms, we can greatly boost the EET process and achieve record high power output. In the first project, we developed and applied an on-chip approach to study the EET, metabolic activity status and behaviors of microbes for maximal current production with real time in-situ microscope observation. The dissimilatory extroelectrogenic bacteria Shewanella oneidensis MR-1 wild type (WT) and its mutant cells (bfe and mtrC/omcA) were used as the model organisms to understand extroelectrogenic biofilm growth, metabolism rate, and current production. Our goal is to specify the various mechanisms of EET process in Shewanella oneidensis MR-1 and its mutant cells under different conditions. Furthermore, based on the insight developed from the on-chip platform, we further develop a rational strategy to boost the transmembrane and extracellular electron transfer processes by loading Shewanella biofilms on reduced graphene oxide/silver nanoparticles (rGO/Ag) scaffolds. Our systematic studies show that the rGO/Ag can release positively charged silver ions, which facilitate Shewanella attachment to rGO/Ag scaffold to form dense biofilms, while at the same time produce transmembrane and outer-membrane Ag nanoparticles to form the Shewanella-Ag hybrids, with greatly enhanced transmembrane and extracellular electron transfer efficiency to improve the bacteria turn-over frequency (TOFs) and boost the overall Shewanella based microbial fuel cells (MFCs) performance. The resulting MFCs with the rGO/Ag anode can output a current density of 38.5 A/m2, a power density of 6.63 W/m2 and a Coulombic efficiency of 81%, greatly outperforming the best Shewanella MFCs reported to date. In the third project, we further show that rGO/Cu scaffolds can exert a similar enhancement effect to produce high performance in the MFC tests, demonstrating universal applicability of our strategy for enhancing the MFC performance.