Identification and Characterization of a Novel Di-(2-ethylhexyl) Phthalate Hydrolase from a Marine Bacterial Strain Mycolicibacterium phocaicum RL-HY01

Phthalic acid esters (PAEs), ubiquitously employed as a plasticizer, have been classified as priority environmental pollutants because of their persistence, bioaccumulation, and endocrine-disrupting properties. As a characterized PAE-degrading strain of marine origin, <i>Mycolicibacterium phocaicum</i> RL-HY01 utilizes di-(2-ethylhexyl) phthalate (DEHP) as its sole carbon and energy source. Genome sequencing and RT-qPCR analysis revealed a previously uncharacterized hydrolase gene (<i>dehpH</i>) in strain RL-HY01, which catalyzes ester bond cleavage in PAEs. Subsequently, recombinant expression of the cloned <i>dehpH</i> gene from strain RL-HY01 was established in <i>Escherichia coli</i> BL21(DE3). The purified recombinant DehpH exhibited optimal activity at 30 °C and pH 8.0. Its activity was enhanced by Co²⁺ and tolerant to most metal ions but strongly inhibited by EDTA, SDS, and PMSF. Organic solvents (Tween-80, Triton X-100, methanol, ethanol, isopropanol, acetone, acetonitrile, ethyl acetate, and <i>n</i>-hexane) showed minimal impact. Substrate specificity assay indicated that DehpH could efficiently degrade the short and long side-chain PAEs but failed to hydrolyze the cyclic side-chain PAE (DCHP). The kinetics parameters for the hydrolysis of DEHP were determined under the optimized conditions, and DehpH had a <i>V_max</i> of 0.047 ± 0.002 μmol/L/min, <i>K_m</i> of 462 ± 50 μmol/L, and <i>k_cat</i> of 3.07 s^-1. Computational prediction through structural modeling and docking identified the active site, with mutagenesis studies confirming Ser228, Asp324, and His354 as functionally indispensable residues forming the catalytic triad. The identification and characterization of DehpH provided novel insights into the mechanism of DEHP biodegradation and might promote the application of the target enzyme.