Title:TiO2 Nanoparticle-Induced Nanowire Formation Facilitates Extracellular Electron Transfer         

Abstract:Semiconductor nanoparticles (NPs) have been reported to facilitate extracellular electron transfer (EET) by increasing the electrical conductivity of electroactive biofilms. However, the underlying molecular mechanisms remain unclear. In this study, we demonstrated the unique role of semiconductor titanium dioxide (TiO₂) NPs in facilitating EET from Geobacter cells to an electrode. Compared to other NPs that include conductor carbon, semiconductor α-Fe₂O₃, and insulator SiO₂, TiO₂ NPs improved the bacterial EET capability most significantly, leading to an approximately 5.1-fold increase in microbial current generation. Cell morphology and gene analysis revealed that TiO₂ NPs specifically induced the formation of conductive nanowires by stimulating pilA expression, which primarily contributed to the enhanced EET in biofilms. In addition, TiO₂ NPs might compensate for the lack of a pili-associated c-cytochrome OmcS in the EET function. This finding had important implications not only for optimizing the performance of electroactive biofilms but also for modulating the ecological impact of NPs in the natural environment.