Properties of a Newly Identified Esterase from <i>Bacillus</i> sp. K91 and Its Novel Function in Diisobutyl Phthalate Degradation

<div><p>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 <i>CarEW</i> gene, which encodes an enzyme that is capable of hydrolyzing ρ-nitrophenyl esters of fatty acids, was cloned from a thermophilic bacterium <i>Bacillus</i> sp. K91 and heterologously expressed in <i>Escherichia coli</i> BL21 using the <i>pEASY</i>-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.</p>