Mechanism study of photo-induced gold nanoparticles formation by Shewanella oneidensis MR-1

Shewanella oneidensis MR-1, a bioelectricity generating bacterium, is broadly used in bioremediation, microbial fuel cell and dissimilatory reduction and recovery of precious metals. Herein, we report for the first time that photo induction as a trigger to stimulate gold nanoparticles (Au@NPs) formation by MR-1, with wavelength and light intensity as two key variables. Results indicated that sigmoidal model is the best fit for Au@NPs formation at various wavelengths (with R-2 > 0.97). Light intensity in terms of photosynthetic photon flux density (PPFD) critically influences the rate constant in the low-light intensity region (PPFD < 20), while wavelength controls the maximum rate constant in the high-light region (PPFD > 20). By deletion of Mtr pathway genes in MR-1, we proposed the mechanism for light induced Au@NP formation is the excitation effect of light on certain active groups and extracellular polymeric substances (EPS) on the cell surface. Also, the release of electrons from proteins and coenzyme complexes enhance electron generation. To the best of our knowledge, this is the first-attempt to explore the effect of photo-induction on Au@NPs production by MR-1, which provides an alternative cost-effective and eco-friendly process in green chemical industry.