Electrochemical analysis for the rapid screening of copper-tolerant bacteria

Environmental pollution caused by heavy metals such as copper is quite severe nowadays. Therefore, screening for strains with solid tolerance to copper is of great importance for the microbial treatment of heavy metal pollution in the environment. Traditional methods of testing copper tolerance rely on bacterial growth on agar plates or liquid cultures. These time-consuming and cumbersome assays use strain growth as an indicator of cellular respiration. In this study, we explored mediated extracellular electron transfer as a rapid and straightforward method to sort copper-tolerant or copper-sensitive bacteria. We tested strains Paenibacillus lautus A (HC_A), Lysinibacillus fusiformis B (HC_B) and Escherichia coli BL21, as well as two microbial consortiums, Natural Consortium and Enriched Consortium. Bacterial cultures were added to a designed three-electrode electrochemical cell with a glassy carbon working electrode and a growth medium supplemented with soluble electron transfer mediators, phenazine methyl sulfate (PMS), or resazurin. The oxidoreduction of the mediators was measured as an electric current and used to monitor cell respiration. Compared with the control without copper treatment, copper-sensitive strains show a reduced current upon copper treatment. Using this new method, we could classify strains as copper tolerant or sensitive in <90 min.