Enhanced removal of PHE-Cd2+ co-contamination by the mixed bacterial cultures of Pseudomonas putida and Arthrobacter sp.: Performance and mechanism

The strain species resource is essential for microbial remediation of PHE (phenanthrene)-Cd²⁺ co-contamination. In this study, the mixed bacterial culture (M) was established to intensively remediate PHE-Cd²⁺ co-contamination using PAHs-degrading bacteria Pseudomonas putida and Arthrobacter sp. with different Cd²⁺ tolerance. The PHE degradation efficiency of the mixed bacterial cultures (M) was 65 %-81 % under different Cd²⁺ concentration of 10–50 mg/L, respectively, which was 1.40–2.98 times that of the individual strains. In addition, strain metabolic enzyme activity, intracellular structure and extracellular polymeric substances (EPS) were carried out under Cd²⁺ stress. Results showed that the catechol 1,2-dioxygenase enzyme (C120) and the electron transport system activity (ETSA) were less adversely affected by Cd²⁺ in mixed bacterial cultures. Transmission electron microscopy images showed that the cells surface of the mixed bacterial cultures (M) could be adsorbed more Cd²⁺ compared to the single strain. The analysis of cell functional groups suggested that C-O-C and C-O groups in EPS mediated the removal of Cd²⁺ in the mixed bacterial culture. Moreover, the Cd²⁺ removal proportion by EPS adsorption of the mixed bacterial cultures accounted for 92 %, 67 %, 57 %, and 52 % under Cd²⁺ stress of 0.5, 10, 25, and 50 mg/L, respectively, which were superior to that of individual strains. This study confirmed the potential application and technical reference of the specific mixed bacterial cultures in the enhanced bioremediation of PHE-Cd²⁺ co-contamination.