Feng Yanmei, Zhang Wenping, Pang Shimei, Lin Ziqiu, Zhang Yuming, Huang Yaohua, Bhatt Pankaj, Chen Shaohua
State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, Guangdong Province Key Laboratory of Microbial Signals and Disease Control, Integrative Microbiology Research Centre, South China Agricultural University, Guangzhou 510642, China.
Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou 510642, China.
Microorganisms. 2020 Apr 26;8(5):625. doi: 10.3390/microorganisms8050625.
Azoxystrobin is one of the most popular strobilurin fungicides, widely used in agricultural fields for decades.Extensive use of azoxystrobin poses a major threat to ecosystems. However, little is known about the kinetics and mechanism of azoxystrobin biodegradation. The present study reports a newly isolated bacterial strain, SH14, utilizing azoxystrobin as a sole carbon source, was isolated from contaminated soils. Strain SH14 degraded 86.3% of azoxystrobin (50 μg·mL) in a mineral salt medium within five days. Maximum specific degradation rate (), half-saturation constant (), and inhibition constant () were noted as 0.6122 d, 6.8291 μg·mL, and 188.4680 μg·mL, respectively.Conditions for strain SH14 based azoxystrobin degradation were optimized by response surface methodology. Optimum degradation was determined to be 30.2 °C, pH 7.9, and 1.1 × 10 CFU·mL of inoculum. Strain SH14 degraded azoxystrobin via a novel metabolic pathway with the formation of -(4,6-dimethoxypyrimidin-2-yl)-acetamide,2-amino-4-(4-chlorophenyl)-3-cyano-5,6-dimethyl-pyridine, and 3-quinolinecarboxylic acid,6,8-difluoro-4-hydroxy-ethyl ester as the main intermediate products, which were further transformed without any persistent accumulative product. This is the first report of azoxystrobin degradation pathway in a microorganism. Strain SH14 also degraded other strobilurin fungicides, including kresoxim-methyl (89.4%), pyraclostrobin (88.5%), trifloxystrobin (78.7%), picoxystrobin (76.6%), and fluoxastrobin (57.2%) by following first-order kinetic model. Bioaugmentation of azoxystrobin-contaminated soils with strain SH14 remarkably enhanced the degradation of azoxystrobin, and its half-life was substantially reduced by 95.7 and 65.6 days in sterile and non-sterile soils, respectively, in comparison with the controls without strain SH14. The study presents SH14 for enhanced biodegradation of azoxystrobin and elaborates on the metabolic pathways to eliminate its residual toxicity from the environment.
嘧菌酯是最常用的甲氧基丙烯酸酯类杀菌剂之一，几十年来广泛应用于农业领域。嘧菌酯的大量使用对生态系统构成了重大威胁。然而，关于嘧菌酯生物降解的动力学和机制却知之甚少。本研究报道了从受污染土壤中分离出的一株新的细菌菌株SH14，该菌株能够以嘧菌酯作为唯一碳源。菌株SH14在矿物盐培养基中5天内降解了86.3%的嘧菌酯（50μg·mL）。最大比降解速率（）、半饱和常数（）和抑制常数（）分别为0.6122 d、6.8291μg·mL和188.4680μg·mL。采用响应面法对菌株SH14降解嘧菌酯的条件进行了优化。确定最佳降解条件为温度30.2℃、pH 7.9、接种量1.1×10 CFU·mL。菌株SH14通过一条新的代谢途径降解嘧菌酯，形成主要中间产物-(4,6-二甲氧基嘧啶-2-基)-乙酰胺、2-氨基-4-(4-氯苯基)-3-氰基-5,6-二甲基吡啶和3-喹啉羧酸6,8-二氟-4-羟基乙酯，这些中间产物进一步转化，无任何持久性累积产物。这是关于微生物中嘧菌酯降解途径的首次报道。菌株SH14还按照一级动力学模型降解了其他甲氧基丙烯酸酯类杀菌剂，包括醚菌酯（89.4%）、吡唑醚菌酯（88.5%）、肟菌酯（78.7%）、啶氧菌酯（76.6%）和氟嘧菌酯（57.2%）。用菌株SH14对受嘧菌酯污染的土壤进行生物强化，显著提高了嘧菌酯的降解率，与未接种菌株SH14的对照相比，在无菌和非无菌土壤中其半衰期分别大幅缩短了95.7天和65.6天。该研究展示了菌株SH14对嘧菌酯的强化生物降解作用，并阐述了消除其环境残留毒性的代谢途径。
