两株蜡状芽孢杆菌对毒死蜱的降解动力学研究

Kinetics of chlorpyrifos degradation by Bacillus cereus strains

利用微生物消除农药污染是一项安全、经济、有效的方法，降解动力学模型的构建有助于理解污染物的生物降解行为和估测系统中特征污染物的浓度变化，菌株对高浓度污染物的降解效果是降解菌在受污染水体中实际应用的关键。本研究采用基础培养基中定量添加毒死蜱和定时取样分析毒死蜱残留浓度的方法，探讨两株蜡状芽孢杆菌（HY-1和HY．2）的接种体培养时间、接种量和降解菌对毒死蜱的降解动力学，同时研究了降解菌对高浓度毒死蜱的降解率。结果表明：HY-1和HY-2最适接种体培养时间分别为10h和19h，接种体培养时间对菌株降解毒死蜱的影响较大。两菌株最适接菌量为8％（v／v），接种量从4％增至8％时，接种量对HY-1降解毒死蜱的影响大于HY-2。当毒死蜱的初始浓度为40mg-L-1、80mg·L-1。、100mg·L-1和120mg·L-1时，一级动力学方程1n（C0／G）=kt可以用来拟合两菌株对毒死蜱的降解动力学及确定降解动力学参数，当毒死蜱初始浓度再次增加时，仅HY-2对毒死蜱的降解符合一级动力学方程。当毒死蜱初始浓度为40～120mg·L-1时，菌株HY-l对毒死蜱的降解速率常数分布在0．0135～0．0157；当毒死蜱初始浓度为40～200mg·L-1时，菌株HY-2的降解速率常数分布在0．0080～0．0153。菌株HY-2比HY-1可以在较高的毒死蜱浓度下发挥降解作用，且降解率较高。因此，两菌株在毒死蜱污染水体的净化去毒方面具有重要意义。

Organophosphorus pesticides have been widely used to control insect pests in agriculture. These compounds have been implicated in several nerve and muscular diseases in humans. Large-scale manufacaring and handling of organophosphate insecticides have caused the contamination of soils, air, surface water and groundwater across the globe. Chlorpyrifos degradation has become an increasingly important area of research in recent years. The current focus has been on the development of cost effective and eco-friendly technologies for treating polluted environments. Biodegradation has offered an efficient and cheap option for such decontamination process. Similarly, biodegradation has also been the main mechanism for removed chlorpyrifos residue, especially in the treatment of discharged wastewater from the varied processes of chlorpyrifos production. The study of the degradation kinetics was useful for understanding biodegradation processes as well as estimating pollutant concentrations. The degradation of high concentration pollutants was critical for developing practical applications of degrading bacteria. In this study, two pure Bacillus cereus strains （HY- 1 and HY-2） were used in chlorpyrifos biodegradation in a batch of shake-flasks. The rate and extent of biodegradation were quantified at different chlorpyrifos initial concentrations （in the range of 40-200 mg·L-1） by B. cereus through adding chorpyrifos to mineralized medium and analyzing chlorpyrifos residue at a definite time. At the same time, the effects of incubation times and size of inoculum on chlorpyrifos degradation rate were determined. The degradation rate of high chlorpyrifos concentration by B. cereus was also measured. The results showed that the appropriate incubation time of inoculum of HY-1 and HY-2 strains were 10 h and 19 h respectively. The data suggested that inoculum incubation time significantly influenced chlorpyrifos degradation efficiency. Optimum inoculum amount for the two strains was 8% （v/v） of total volume. The effect of inoculum size on HY-1 degradation function was greater than that of HY-2 as the ratio increased from 4% to 8%. The simulated results suggested thatthe fit of the first-order kinetics model [ln（Co/Ct）=kt] was good for initial chlorpyrifos concentrations of 40 mg·L-1, 80 mg·L-1, 100 mg·L-1 and 120 mg·L-1. With further increases in chlorpyrifos concentration, only HY-2 followed the first-order kinetics model in terms of chlorpyrifos degradation. When chlorpyrifos concentration was within 40～120 mg·L-1, HY-1 degradation efficiency constant was within 0.013 5～0.015 7. Similarly, HY-2 degradation efficiency constant was within 0.008 0～0.015 3 when the chlorpyrifos concentration was 40～200 mg·L-1. HY-2 strain was possibly more suitable for higher chlorpyrifos concentration than HY-1 in terms of chlorpyrifos degradation, with HY-2 degradation rate relatively higher as well. The results suggested that further research was needed on the two microbes to fully understand their use as potential bio-agents in chlorpyrifos water contaminated remediation.