Combined application of resveratrol and a ryegrass endophyte in PAH-contaminated soil remediation and its impact on soil microbial communities†

The unique capacity of certain plant endophytes to degrade organic pollutants has garnered considerable interest in recent years. However, it remains uncertain whether endophytes can maintain high degradation activity after in vitro culture and whether they can be used directly in the remediation of contaminated soils. This study reveals that resveratrol, a plant secondary metabolite, selectively boosts the degradation of polycyclic aromatic hydrocarbons (PAHs) by endophytic Methylobacterium extorquens C1 (C1) in vitro, while exerting negligible effects on the activity of indigenous soil bacteria. For the first time, a combined application of C1 and resveratrol was employed in the remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil. The findings indicate that the sole use of resveratrol failed to promote the removal of PAHs by indigenous soil microorganisms, whereas sole application of C1 boosted Methylobacterium-related PAH-degrading bacterial abundance, enhancing PAH removal, yet concurrently reduced overall soil microbial diversity. The combination of resveratrol and C1 not only stimulated the PAH removal but also mitigated the impact of C1 on the soil microbial community structure when C1 was applied individually. Specifically, the optimal removal efficacy was achieved with a treatment combination of 5 mg kg⁻¹ resveratrol and 1.2 × 10⁷ CFU kg⁻¹ of C1, leading to a 130% and 231% increase in the removal of phenanthrene and acenaphthene, respectively, over a 15 days period. This study proposes a novel approach for the bioremediation of organic-contaminated soil by using the specific biological response of plant endophytic bacteria to secondary metabolites.