Using electrical signals of microbial fuel cells to detect copper stress on soil microorganisms

Summary A method based on microbial fuel cells ( MFCs ) was used to evaluate the effects of copper ( Cu 2+ ) on soil microorganisms. Soil spiked with 50–400 mg kg −1 of Cu 2+ as CuCl 2 was incubated for 24 hours before being packed into the MFC anode chambers and assayed for dehydrogenase activity ( DHA ), substrate‐induced respiration ( SIR ) and microbial biomass carbon ( C mic ). Soil was amended with 5% ( w / w ) glucose to accelerate ‘start‐up’ and improve power generation, followed by 150 hours of operation. Anode biofilm and soil was extracted to recover total nucleic acids and the 16S rRNA gene was subjected to PCR‐DGGE , sequencing and phylogenetic analysis. Results showed that increases in soil Cu 2+ concentrations reduced voltage and postponed start‐up. The quantity of generated electrons within 48 hours was 32.5 coulomb (C) in the without‐ Cu control and decreased with increasing Cu 2+ concentrations (11.7, 7.7, 2.0 and 1.3 C under 50, 100, 200 and 400 mg kg −1 Cu 2+ , respectively). Cyclic voltammetry identified decreased soil electrochemical activity with increasing Cu 2+ concentrations. The results indicate that Cu 2+ reduced electrical signals by inhibiting the electrochemical activity, metabolic activity and biomass of microorganisms. The 16S sequences of recovered anodic bacteria were assigned to Firmicutes , including Bacillaceae , Acetobacteraceae , Clostridium , Bacillus and Sporolactobacillus . In general, the DGGE band intensity of anodic bacteria decreased with increasing Cu 2+ concentrations, except for bands assigned to Firmicutes and Bacillus , which increased with increasing Cu 2+ concentrations. We suggest that the short‐term electrical signals generated from MFCs with contaminated soil can be used to assess the toxic effect of heavy metal pollutants on soil microorganisms.