Kinetics and New Mechanism of Azoxystrobin Biodegradation by an Ochrobactrum anthropi Strain SH14

Yanmei Feng; Wenping Zhang; Shimei Pang; Ziqiu Lin; Yuming Zhang; Yaohua Huang; Pankaj Bhatt; Shaohua Chen

doi:10.3390/microorganisms8050625

Kinetics and New Mechanism of Azoxystrobin Biodegradation by an Ochrobactrum anthropi Strain SH14

Microorganisms. 2020 Apr 26;8(5):625. doi: 10.3390/microorganisms8050625.

Authors

Yanmei Feng^{1

2}, Wenping Zhang^{1

2}, Shimei Pang^{1

2}, Ziqiu Lin^{1

2}, Yuming Zhang^{1

2}, Yaohua Huang^{1

2}, Pankaj Bhatt^{1

2}, Shaohua Chen^{1

2}

Affiliations

¹ 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.
² Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou 510642, China.

Abstract

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, Ochrobactrum anthropi SH14, utilizing azoxystrobin as a sole carbon source, was isolated from contaminated soils. Strain SH14 degraded 86.3% of azoxystrobin (50 μg·mL^-1) in a mineral salt medium within five days. Maximum specific degradation rate (q_max), half-saturation constant (K_s), and inhibition constant (K_i) were noted as 0.6122 d^-1, 6.8291 μg·mL^-1, and 188.4680 μg·mL^-1, 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 × 10⁷ CFU·mL^-1 of inoculum. Strain SH14 degraded azoxystrobin via a novel metabolic pathway with the formation of N-(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 O. anthropi SH14 for enhanced biodegradation of azoxystrobin and elaborates on the metabolic pathways to eliminate its residual toxicity from the environment.

Keywords: Ochrobactrum anthropi SH14; azoxystrobin; biodegradation; kinetics; metabolic pathway.

Grants and funding

31401763/National Natural Science Foundation of China