Enhanced bioremediation of petroleum-contaminated soil by sophorolipids-modified biochar in combination with Iris lacteal Pall: metagenomic and metabolomic analyses

In this study, sophorolipids (SLs)-modified KOH-activated biochar (KBC-SLs) in combination with iridaceae plant- Iris lacteal Pall, was used to improve the bioremediation of petroleum hydrocarbons (PHs)-contaminated soil. The bioremediation ratio of PHs in the KBC-SLs, KBC+SLs and KBC were 56.7%, 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, metagenomic analysis showed that the abundance of Actinomycetota and Acidobacteriota, the dominant PHs degrading bacteria in KBC-SLs, increased by 34.3% and 23.3%, respectively, and the abundance of functional genes for PHs degradation, such as alkB, nidB, and xylC, increased significantly by 32.3%, 131.1%, and 33.4%, respectively. Metabolomics analyses showed that KBC-SLs promoted the metabolic processes of PHs and the microbial metabolism of PHs became more active. Fatty acid degradation and polycyclic aromatic hydrocarbons (PAHs) degradation were both up-regulated, suggesting that KBC-SLs significantly promoted the metabolic processes of PHs. Association analysis of metagenomics and metabolomics showed strong positive correlations between PHs metabolites and PHs degrading bacteria, such as palmitic acid with Bacteroidota, myristic acid with Acidobacteriota. Besides, strong positive correlations were observed between PHs metabolites and PHs degradation genes, such as m-toluic acid with nahE (K14585) and xylM (K15757). Additionally, the application of KBC-SLs had promoted plant growth by increasing plant height, root vitality and improving soil enzyme activities, which in turn enhanced the effectiveness of bioremediation of petroleum-contaminated soil. This study provides new evidence about biochar-enhanced bioremediation of petroleum-contaminated soils and offers insights into the green and sustainable remediation of petroleum-contaminated soils.