Synergistic toxic effects of ball-milled biochar and copper oxide nanoparticles on Streptomyces coelicolor M145.

The toxic effects of multi-nanomaterial systems are receiving increasing attention owing to their inevitable release of various nanomaterials. Knowledge of the bioavailability of the new carbon material ball-milled biochar (BMB) and its synergistic toxicity with metal oxide nanoparticles in bacteria is currently limited. In this study, the interactions of BMB with copper oxide nanoparticles (CuO NPs) and their synergistic toxicity towards Streptomyces coelicolor M145 were analyzed. Results showed that the cytotoxicity, ROS level and permeability of cells changed greatly with the pyrolysis temperatures of biochar and the concentrations of CuO NPs. The greatest cytotoxicity (up to 63.1%) was achieved by adding 20 mg/L CuO NPs to BMB700. The ROS level and cell permeability of this treatment was also the highest, about 4.2 folds and 2.9 folds greater than that of control, respectively. The combination of 10 mg/L BMB700 with 10 mg/L CuO NPs can maximize production of antibiotics, with the yield of undecylprodigiosin (RED) and actinorhodin (ACT) 3.0 times and 4.2 times higher than that in the control, respectively, and the change trend of related genes was consistent with that of antibiotics production. Mechanism analysis showed that the different adsorption capacity of BMB of different pyrolysis temperatures on copper ions played a vital role in the synergistic toxicity, and the increase in cell membrane permeability caused by cell collisions with particles was also an important reason for cytotoxicity. Overall, the synergistic toxicity of BMB with other NPs varies the pyrolysis temperatures, when considering the synergistic toxicity of these materials, the preparation conditions need to be taken into account so as to assess their environmental risks more accurately. On the other hand, this research may provide a new approach for the antibiotic industry to increase its output.