Copper reducing power

In vitro copper reducing power of spent media obtained from different E. coli strains was measured using bathocuproine disulfonate (BCDS) (Sigma–Aldrich), following the method described by Volentini et al. (2011). This chelator forms a colored complex with cuprous ions, having a λmax at 480 nm (Poillon and Dawson, 1963). Cells were grown for 18 h at 37°C in M9 medium. Then, supernatants were filter sterilized and incubated with 100 μM CuSO₄ and 200 μM BCDS. The absorbance at 480 nm was determined and Cu⁺ concentrations were calculated by comparison to a standard curve obtained in M9 medium supplemented with different Cu²⁺ concentrations and 25 mM ascorbic acid as a reducing agent.