Enzymatic degradation of phthalate esters in the environment: Advances, challenges and opportunities
Shengwei Sun, Per‐Olof Syrén
Abstract
• The global production of phthalate esters (PAEs) is ∼ 8 million tons per year. • Enzymatic degradation plays a key role in the removal of PAE contaminants. • Only a limited number of PAE hydrolases have been fully characterized so far. • About 6 novel PAE-degrading enzymes were identified from metagenomes. • Steric hindrance and electrostatic repulsion affect the PAE binding to the enzyme. The continued growth in phthalate esters (PAEs) production (∼8 million tons per year) has led to the increased emissions of PAEs into atmospheric, soil, and aquatic environments, posing a serious threat to human and animal health. Microbial enzyme-mediated degradation is an effective remediation strategy for removing PAE contaminants in the environment. Several hydrolases from both culturable and non-culturable microorganisms have been identified with outstanding degradation capacities against PAEs. A hydrolase identified from Glutamicibacter sp. strain 0426 could completely degrade 300 mg/L of dibutyl phthalate (DBP) within 12 h at 32℃ and pH 6.9, and an esterase which was screened from a metagenomic library exhibited high hydrolytic activity (128 U/mg) toward DBP at 40℃ and pH 7.5. However, there are still only a limited number of PAE-degrading enzymes that have been fully characterized so far. Herein, we show the significant influence of PAEs on plastic recycling and environmental pollution. We review recent advances in the identification and isolation of PAE-degrading enzymes from diverse environments. We highlight the potential of metagenomic analyses for exploring novel and powerful PAE hydrolases. Moreover, we discuss a possible enzyme-catalyzed reaction mechanism for PAE hydrolysis given the scarce experimental evidence. The substrate specificity among different monoalkyl/dialkyl PAE hydrolases is attributed to the steric hindrance and electrostatic repulsion affecting the PAE binding to an enzyme. Furthermore, we discuss different directed evolution strategies for improving the performance of PAE-degrading enzymes. Several challenges and future directions in research on PAE-degrading enzymes are also identified.