Abstract
The widely used plasticizer phthalate esters (PAEs) have become a public concern because of their effects on environmental contamination and toxicity on mammals. However, the biodegradation of PAEs, especially diisobutyl phthalate (DiBP), remains poorly understood. In particular, genes involved in the hydrolysis of these compounds were not conclusively identified. In this study, the CarEW gene, which encodes an enzyme that is capable of hydrolyzing ρ-nitrophenyl esters of fatty acids, was cloned from a thermophilic bacterium Bacillus sp. K91 and heterologously expressed in Escherichia coli BL21 using the pEASY-E2 expression system. The enzyme showed a monomeric structure with a molecular mass of approximately 53.76 kDa and pI of 4.88. The enzyme exhibited maximal activity at pH 7.5 and 45°C, with ρ-NP butyrate as the best substrate. The enzyme was fairly stable within the pH range from 7.0 to 8.5. High-pressure liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS) were employed to detect the catabolic pathway of DiBP. Two intermediate products were identified, and a potential biodegradation pathway was proposed. Altogether, our findings present a novel DiBP degradation enzyme and indicate that the purified enzyme may be a promising candidate for DiBP detoxification and for environmental protection.
Highlights
Phthalate esters (PAEs) are important synthetic organic compounds applied as plasticizers on a massive scale in the industrial production of plastics, and used as additives in the manufacture of adhesives, paints, lacquers, cardboard, cosmetics, and so on [1]
A newly identified esterase Est1 from S. acidophilus DSM10332 degraded PAEs to their corresponding monoalkyl PAEs [29]. These observations and our results suggested that phthalate esterases are a diverse group of distinct enzymes involved in the cleavage of the carboxylic ester linkages of PAEs
CarEW is capable of hydrolyzing diisobutyl phthalate (DiBP) to monoisobutyl phthalate (MiBP) and phthalic acid (PTH)
Summary
Phthalate esters (PAEs) are important synthetic organic compounds applied as plasticizers (softeners) on a massive scale in the industrial production of plastics, and used as additives in the manufacture of adhesives, paints, lacquers, cardboard, cosmetics, and so on [1]. PAEs can bind to estrogen receptors and disrupt the endocrine system [4]. These compounds can induce reproductive toxicity [5], hormonal disorders [6], hepatic peroxisome proliferation [7], hepatocellular tumors [8], and may harm fetal health [9]. This increased understanding has fundamentally changed the perception on the environmental and health risks presented by PAEs and have raised an important issue on their environmental fate
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