High-level extracellular production and immobilisation of methyl parathion hydrolase from Plesiomonas sp. M6 expressed in Pichia pastoris.

Methyl parathion hydrolase (MPH) hydrolyses methyl parathion efficiently and specifically. Herein, we produced MPH from Plesiomonas sp. M6 using a Pichia pastoris multi-copy expression system. The original signal peptide sequence of the target gene was removed, and a modified coding sequence was synthesised. Multi-copy expression plasmids containing MPH were constructed using pHBM905BDM, and used to generate recombinant strains containing 1, 2, 3 or 4 copies of the MPH gene. The results showed that a higher target gene copy number increased the production of recombinant MPH (MPH-R), as anticipated. The expression level of the recombinant strain containing four copies of the MPH gene was increased to 1.9 U/ml using 500 ml shake flasks, and the specific activity was 15.8 U/mg. High-density fermentation further increased the target protein yield to 18.4 U/ml. Several metal ions were tested as additives, and Ni, Co and Mg at a concentration of 1 mM enhanced MPH-R activity by 196%, 201% and 154%, respectively. Enzyme immobilisation was then applied to overcome the difficulties in recovery, recycling and long-term stability associated with the free enzyme. Immobilised MPH-R exhibited significantly enhanced thermal and long-term stability, as well as broad pH adaptability. In the presence of inhibitors and chelating agents such as sodium dodecyl sulphate (SDS), immobilised MPH-R displayed 2-fold higher activity than free MPH-R, demonstrating its potential for industrial application.