Metagenomic insight into the mechanisms of accelerated di-2-ethylhexyl phthalate (DEHP) degradation in vermicomposting

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Earthworms can expedite di-(2-ethylhexyl) phthalate (DEHP) degradation in soils, but limited information is available on the key DEHP-degradation pathways and related genes during the vermicomposting process. In this study, DEHP degradation, degradation-related genes and bacterial communities were investigated by metagenomic analysis. DEHP degradation efficiency was significantly and 65.69% higher in vermicomposting treatment than natural soils. Earthworm supplement remarkably increased the contents of humic acid, humus and fulvic acid in soils. Both humic acid and earthworm gut positively stimulated soil microbes potentially responsible for DEHP degradation. Betaprotebacteria, Acidobacteria, Variovorax, Hydrogenophaga, Limnobacter, Ramlibacter, Pseudomonas, Acinetobacter, Paracoccus and Achromobacter significantly contributed to DEHP degradation pathways. From functional gene analysis, there were remarkable differences in dominant DEHP degradation pathways between soils (catechol pathway), earthworm cast (protocatechuate pathway), and earthworm gut (protocatechuate and catechol pathways). Our findings proposed two possible mechanisms of earthworms in accelerating DEHP degradation, stimulating the activities of indigenous degraders to augment the catechol pathway in soils and providing an extra protocatechuate pathway in earthworm gut. This study, for the first time, offers new insights into the impacts of vermicomposting on DEHP degradation genes and pathways, providing valuable scientific evidence for improving DEHP bioremediation in contaminated agricultural soils.