Integrated multi-omics investigations reveal the key role of synergistic microbial networks in removing plasticizer di-(2-ethylhexyl) phthalate from estuarine sediments
Authors: Wei Sean Ting-Shyang , Chen Yi-Lung , Wu Yu-Wei , Wu Tien-Yu , Lai Yi-Li , Wang Po-Hsiang , Ismail Wael , Lee Tzong-Huei , Chiang Yin-Ru 
Published: March 2021

Di-(2-ethylhexyl) phthalate (DEHP) is the most widely used plasticizer worldwide with an annual global production of over eight million tons. Because of its improper disposal, endocrine-disrupting DEHP often accumulates in estuarine sediments in industrialized countries at sub-millimolar levels, resulting in adverse effects on both ecosystems and human beings. The microbial degraders and biodegradation pathways of DEHP in O2-limited estuarine sediments remain elusive. Here, we employed an integrated meta-omics approach to identify the DEHP degradation pathway and major degraders in this ecosystem. Estuarine sediments were treated with DEHP or its derived metabolites,o-phthalic acid and benzoic acid. The rate of DEHP degradation in denitrifying mesocosms was two times slower than that ofo-phthalic acid, suggesting that side-chain hydrolysis of DEHP is the rate-limiting step of anaerobic DEHP degradation. On the basis of microbial community structures, functional gene expression, and metabolite profile analysis, we proposed that DEHP biodegradation in estuarine sediments is mainly achieved through synergistic networks between denitrifying proteobacteria.AcidovoraxandSedimenticolaare the major degraders of DEHP side-chains; the resultingo-phthalic acid is mainly degraded byAestuariibacterthrough the UbiD-dependent benzoyl-CoA pathway. We isolated and characterizedAcidovoraxsp. strain 210-6 and its extracellular hydrolase, which hydrolyzes both alkyl side-chains of DEHP. Interestingly, genes encoding DEHP/MEHP hydrolase and phthaloyl-CoA decarboxylase—key enzymes for side-chain hydrolysis ando-phthalic acid degradation, respectively—are flanked by transposases in these proteobacterial genomes, indicating that DEHP degradation capacity is likely transferred horizontally in microbial communities.

Importance

Xenobiotic phthalate esters (PAE) have been produced on a considerably large scale for only 70 years. The occurrence of endocrine-disrupting di-(2-ethylhexyl) phthalate (DEHP) in environments has raised public concern, and estuarine sediments are major DEHP reservoirs. Our multi-omics analyses indicated that complete DEHP degradation in O2-limited estuarine sediments depends on synergistic microbial networks between diverse denitrifying proteobacteria and uncultured candidates. Our data also suggest that the side-chain hydrolysis of DEHP, rather thano-phthalic acid activation, is the rate-limiting step in DEHP biodegradation within O2-limited estuarine sediments. Therefore, deciphering the bacterial ecophysiology and related biochemical mechanisms can help facilitate the practice of bioremediation in O2-limited environments. Furthermore, the DEHP hydrolase genes of active DEHP degraders can be used as molecular markers to monitor environmental DEHP degradation. Finally, future studies on the directed evolution of identified DEHP/MEHP hydrolase would bring a more catalytically efficient DEHP/MEHP hydrolase into practice.