Biochar inoculated with Pseudomonas putida alleviates its inhibitory effect on biodegradation pathways in phenanthrene-contaminated soil

Controversial results are reported whereby biodegradation of polycyclic aromatic hydrocarbons (PAHs) can be promoted or inhibited by biochar amendment of soil. Metabolomics was applied to analyze the metabolic profiles of amendment with biochar (BB) and biochar inoculated with functional bacteria ( Pseudomonas putida ) (BP) involved in phenanthrene (PHE) degradation. Additionally, metagenomic analysis was utilized to assess the impact of different treatments on PHE degradation by soil microorganisms. Results indicated that BB treatment decreased the PHE biodegradation of the soil indigenous bacterial consortium, but BP treatment alleviated this inhibitory effect. Metabolomics revealed the differential metabolite 9-phenanthrol was absent in the BB treatment, but was found in the control group (CK), and in the treatment inoculated with the Pseudomonas putida (Ps) and the BP treatment. Metagenomic analysis showed that biochar decreased the abundance of the cytochrome P450 monooxygenase (CYP116), which was detected in the Pseudomonas putida , thus alleviating the inhibitory effect of biochar on PHE degradation. Moreover, a noticeable delayed increase of functional gene abundance and enzymes abundance in the BB treatment was observed in the PHE degradation pathway. Our findings elucidate the mechanism of inhibition with biochar amendment and the alleviating effect of biochar inoculated with degrading bacteria.