The authors report that a marine Shewanella sp. CNZ‐1 is capable of producing Au NPs under various conditions. Results showed that initial concentration of Au(III), pH values and electron donors affected nucleation of Au NPs by CNZ‐1, resulting in different apparent color of the as‐obtained bio‐Au NPs, which were further characterized by UV‐Vis, TEM, XRD, and XPS analyses. Mechanism studies revealed that Au(III) was first reduced to Au(I) and eventually reduced to EPS‐coated Au0 NPs. FTIR and FEEM analyses revealed that some amides and humic acid‐like matters were involved in the production of bio‐Au NPs through CNZ‐1 cells. In addition, the authors also found that the catalytic activity of bio‐Au NPs for 4‐nitrophenol (4‐NP) reduction could be enhanced by various metal ions (Ca2+, Cu2+, Co2+, Fe2+, Fe3+, Ni2+, Sr2+, and Cr3+) and metal oxides (Fe3O4, Al2O3, and SiO2), which is beneficial for their further practical application. The maximum zero‐order rate constant k
1 and first‐order rate constant k2 of all metal ions/oxides supplemented systems can reach 99.65 mg/(L.min) and 2.419 min−1, which are 11.3‐ and 12.6‐fold higher than that of control systems, respectively. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2727, 2019.