Immobilization of the crude enzyme extracted from Stenotrophomonas sp. GYH within modified zeolitic imidazolate framework (ZIF-8-NH2) and its application in trichloromethane removal

Abstract

Enzyme immobilization, due to its higher effective density in a limited micro space, can effectively improve the removal efficiency for some recalcitrant compounds. Metal–organic frameworks (MOFs) have been identified as having attractive properties for the immobilization of enzymes, such as high surface area, large internal pore volumes and easily adjustable pore size. In the present study, a new immobilization carrier was synthesized through the modification of zeolitic imidazole framework-8 (ZIF-8) by 2-aminobenzimidazole, which was employed for enzymes immobilization for the first time. The immobilized bio-enzyme was extracted from trichloromethane (TCM) degrader Stenotrophomonas sp. GYH, and identified through label-free quantitative proteomics. Based on the metabolites detection and molecular docking, a proper degradation pathway for TCM was proposed, in which some key enzymes were tagged with the specific role. XRD, BET, and FTIR analyses proved that ZIF-8-NH₂ was proper as the immobilization carrier. The bio-enzyme@ZIF-8-NH₂ prepared under the best immobilized conditions had a similar relative enzyme activity to that of free enzyme (the Michaelis kinetic constant K_m was 3.86 and 3.78 ​min⁻¹), but it had better pH and temperature adaptability (pH 5−9 and temperature 10−50 ​°C), better storage stability (83% and 40% of the initial enzyme activity at 30 ​d) and so on. The density functional theory (DFT) results show that the ZIF-8-NH₂ carrier has a better TCM and CO₂ adsorption energy, which is consistent with the fact that the bio-enzyme@ZIF-8-NH₂ had better TCM degradation efficiency and less CO₂ emission to the surroundings.