Metagenomic analysis reveals the roles of Actinobacteria in plasticizer-contaminated landfills and aids in identifying key degraders

Phthalate ester (PAE) contamination, particularly from dibutyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP), originating from landfills and released into the environment, poses a significant concern. Understanding PAE biodegradation is crucial for developing bioremediation strategies. This study used cover material from a 1-month-old landfill for soil microcosms. Indigenous microbes effectively removed 300 mg kg^-1 of DBP and DEHP as individual and mixed substrates, achieving complete DBP removal and 70% DEHP removal at room temperature (27-30 °C) and 37 °C. Actinobacteria were dominant, indicating potential active PAE-degraders. Shotgun metagenomic analysis revealed an increased abundance of potential PAE catabolic genes, such as those encoding esterase, lipase, and dioxygenase, under all conditions, mainly associated with Streptomyces, Saccharopolyspora, Nocardia, Nocardioides, and Amycolatopsis. The genes associated with Saccharopolyspora were abundant at 37 °C, while those related to Nocardia and Actinomadura were prevalent at room temperature, suggesting temperature preferences. The genera Saccharopolyspora and Actinomadura have not been linked to PAE degradation, indicating potential novel PAE degraders. Furthermore, PAE-degrading bacteria were isolated using media designed from metagenomic data and were categorized into Streptomyces, Amycolatopsis, and Nocardia. This work highlights the roles of rare taxa and provides insights into potential novel PAE degraders, emphasizing the need for further research into these organisms.