Effect of biochar-immobilized Sphingomonas sp. PJ2 on bioremediation of PAHs and bacterial community composition in saline soil

This study aimed to investigate the bioremediation efficiency and bacterial regulation mechanism of biochar-immobilized bacterium (BM) in polycyclic aromatic hydrocarbon (PAH)-contaminated saline soil by conducting pot experiments. In BM treatment, PAH-degrading strain Sphingomonas sp. PJ2 was inoculated into biochar produced at 400 °C and 600 °C using the pine needles (BM400 and BM600). The removal rates of PAHs, soil physicochemical properties, abundance of PAH-ring hydroxylating dioxygenase (PAH-RHD), and bacterial community composition were determined. After 60 days of bioremediation, BM treatment significantly (P < 0.05) increased the removal rate of PAHs compared with biochar and PJ2 alone (15.94% and 37.3%, respectively). BM treatment clearly improved the physicochemical properties of saline soil. Moreover, the amount of Gram-positive PAH degraders increased in BM-treated soils compared with other treatments, and their gene abundance had a strong positive correlation with the removal rates of PAHs in soils (r = 0.896; P < 0.01). Furthermore, BM treatment increased the abundance of Sphingomonas genus, indicating that the strain PJ2 could survive and colonize in PAH-contaminated saline soil under the protection of biochar. This study provided an effective and green approach for the remediation and improvement of the PAH-contaminated saline soil.