Synergistic improvement of Shewanella loihica PV-4 extracellular electron transfer using a TiO2@TiN nanocomposite.

• A novel TiO 2 @TiN nanocomposite enhances the extracellular electron transfer of bacteria. • TiO 2 @TiN nanocomposites reduce charge transfer resistance at biofilm-electrode interfaces. • The biosynthesis of electron transfer mediators is enhanced by a TiO 2 @TiN nanocomposite. • Cytochrome c expression can be increased by a TiO 2 @TiN nanocomposite. Extracellular electron transfer (EET) allows microorganisms to perform anaerobic respiration using insoluble electron acceptors, including minerals and electrodes. EET-based applications require efficient electron transfer between living and non-living systems. To improve EET efficiency, the TiO 2 @TiN nanocomposite was used to form hybrid biofilms with Shewanella loihica PV-4 (PV-4). Chronoamperometry showed that peak current was increased 4.6-fold via the addition of the TiO 2 @TiN nanocomposite. Different biofilms were further tested in a dual-chamber microbial fuel cell. The PV-4 biofilm resulted a maximum power density of 33.4 mW/m2, while the hybrid biofilm of the TiO 2 @TiN nanocomposite with PV-4 yielded a 92.8% increase of power density. Electrochemical impedance spectroscopy analyses showed a lower electron-transfer resistance in the hybrid biofilm. Biological measurements revealed that both flavin secretion and cytochrome c expression were increased when the TiO 2 @TiN nanocomposite presented. These results demonstrated that the TiO 2 @TiN nanocomposite could synergistically enhance the EET of PV-4 through altering its metabolism. Our findings provide a new strategy for optimizing biotic-abiotic interactions in bioelectrochemical systems. [ABSTRACT FROM AUTHOR]