Enhancing phyto-microbial remediation of petroleum-contaminated soil using sophorolipid-modified biochar: Metagenomic and metabolomic insights.

We developed KOH-activated biochar (K-BC) and sophorolipid-modified K-BC (S-K-BC) for enhancing phyto-microbial remediation of petroleum hydrocarbon (PH)-contaminated soil using Iris lactea Pall. Subsequently, three remediation systems were established: KBC-SLs (Iris lactea Pall. + 2 wt% S-K-BC), KBC + SLs (Iris lactea Pall. + 2 wt% K-BC + 3 × 10^-4 mol SLs), and KBC (Iris lactea Pall. + 2 wt% K-BC) to study the enhancing effect on phyto-microbial remediation. The removal ratio of petroleum hydrocarbons (PHs) in KBC-SLs, KBC + SLs and KBC were 64.0 %, 53.6 % and 46.7 %, respectively, which were higher than that of the plant alone treatment group (27.8 %). After 90 days of remediation experiments, metagenomics showed that KBC-SLs increased the abundance of PH-degrading bacteria (Actinomycetota +34.3 %, Acidobacteriota +23.3 %) and key genes (alkB +32.3 %, nidB +49.8 %, xylC +33.4 %). Metabolomics revealed that KBC-SLs boosted PHs degradation by upregulating fatty acid and polycyclic aromatic hydrocarbons (PAHs) metabolic pathways. Association analysis of metagenomics and metabolomics showed strong positive correlations between PHs metabolites and PHs degrading microorganisms, such as palmitic acid with Bacteroidota, myristic acid with Acidobacteriota. And, strong positive correlations were observed between PHs metabolites and PHs degradation genes, such as m-toluic acid with nahE (K14585) and xylM (K15757). Additionally, KBC-SLs had enhanced the phyto-microbial remediation of PH-contaminated soil by boosting plant growth, root activity, soil enzymes, and plant-microbe synergy. This study confirms that S-K-BC effectively enhances the phyto-microbial remediation of PH-contaminated soil, providing valuable insights into green and sustainable remediation technologies.