Generation and cytotoxicity of free radicals during biodegradation of anthracene by Ochrobactrum sp. strain B01

Persistent free radicals (PFRs) derived from the abiotic transformation of polycyclic aromatic hydrocarbons (PAHs) have been well documented as emerging contaminants, yet the formation and the role of PFRs in biodegradation process is unknown. Herein, the potential generation of PFRs and reactive oxygen species like O₂•−, H₂O₂, and •OH, as well as their possible effects in the biodegradation of anthracene by Ochrobactrum sp. strain B01 were investigated systematically. Results unexpectedly showed that PFRs were formed in amounts rising from 1 to 3 d and reaching an equilibrium, consistent with the biodegradation trend of anthracene. Meanwhile, PFRs induced the formation of O₂•− and H₂O₂, rather than •OH, enhanced antioxidant enzyme activities, and inhibited microbial abundance, inducing cytotoxic effects. Scavenger trapping experiments revealed that the cytotoxicity was mainly due to the ROS, which injured the cell wall and cause the inactivation of bacteria, thus inhibiting the biodegradation of anthracene by Ochrobactrum. Overall, these findings uncovered that the intrinsic mechanism of the difficulty in PAHs microbial biodegradation may be due to the production of PFRs, which is helpful in designing and optimizing more effective bioremediation technologies to remediate PAHs in soils.