Optimization of the extraction of alkaline phosphatase from Lactobacillus rhamnosus and the mechanism underlying the degradation of organophosphorus pesticides

Abstract:

[Background] China, one of the world's largest agricultural economy, has seen the large-scale use of pesticides. However, the overuse of pesticides, which has led to high detection rate, has threatened the environment and human health.[Objective] Alkaline phosphatase (ALP) can degrade organophosphorus pesticides. Therefore, we optimized the extraction of ALP from Lactobacillus rhamnosus Z23 (LGG Z23) and explored the mechanism underlying the degradation of organophosphorus pesticides. [Methods] Single factor test and orthogonal test were used to optimize the extraction. The enzyme activity was determined by detecting the amount of p-nitrophenol released. Fractional precipitation and chromatography were employed for the purification of ALP. The degradation rate of organophosphorus pesticides was determined based on the inhibition of acetylcholinesterase. [Results] The optimum conditions for extracting ALP from LGG Z23 were as follows:disruption of cells for 15 min at 450 W, material-liquid ratio (mass to volume ratio) of 1:6, and pH 10.0. Under the conditions, the activity of ALP was (4.95±0.26) U/mL, 2.11 times higher than that before optimization. The degradation rate of 6 organophosphorus pesticides was in the order of DDVP (95.79%±0.01%)>methyl parathion (90.69%±0.03%)>chlorpyrifos (88.90%±0.02%)>trichlorfon (86.07%±0.03%)>malathion (85.31%±0.02%)>dimethoate (83.18%±0.03%). Among them, the activity of degrading DDVP and methyl parathion was the highest (over 90%), and the difference was significant (P<0.05). [Conclusion] The result lays a theoretical basis and provides data for the application of ALP from LGG Z23.

Key words:Lactobacillus rhamnosus;alkaline phosphatase;extraction conditions;organophosphorus pesticides;degradation rate