Highly Efficient In-Situ Cleaner Degradation of Difenoconazole by Two Novel Dominant Strains: Microflora Diversity, Monoclonal Isolation, Growth Factor Optimization, Intermediates, and Pathways

Abstract

The non-point source pollution of difenoconazole (DIF) has become a serious environmental issue, increasingly causes indelible damages to eco-environment and human health due to its toxicity, persistence, and biomagnification. An eco-friendly, cost-effective, and efficient technology is imperative towards a sustainable agricultural production. Herein, we successfully screened a dominant microflora of efficiently degrading DIF and investigated its microbial diversity. Two novel degrading strains were isolated and identified as Phyllobacterium sp. (T-1) and Aeromonas sp. (T-2). The results of growth factor optimization indicated that degradation rates of DIF (C 0 =20 mg/L) by strain T-1 and T-2 were up to 96.32% and 97.86% within 14 d, respectively, under the optimal conditions. Moreover, there no obvious synergy between strain T-1 and T-2. From catalytic kinetics of enzymes, intracellular enzyme of strain T-1 dominated degradation of DIF (C 0 =20 mg/L) entirely with degradation rate of 82.4% (48 h), the extracellular enzyme showed little catalytic activity. However, degrade rates of DIF (C 0 =20 mg/L) by both intracellular and extracellular enzymes of strain T-2 were 77.99% and 26.73% within 48 h, respectively. Moreover, these enzymes remained an undiminished catalytic activity within 48 h. DIF was degraded by strain T-1 to three transformation products (DIF-TPs 406, DIF-TPs 216, and DIF-TPs 198) undergoing hydroxyl substitution, hydrolysis, cleavage of ether bond between benzene rings, and rearrangement, while two additional products (DIF-TPs 281 and DIF-TPs 237) were generated with  biodegradation of strain T-2, excepting for DIF-TPs 406 and DIF-TPs 216, involving hydrolysis, hydroxylation, and ether bond cleavage between benzene rings. Moreover, QSAR simulation showed that these by-products were almost much lower toxicity or even non-toxic than DIF. This study not only provides an in depth understanding of DIF bioelimination, but also be instrumental in cleaner management of DIF-contaminated soil, finally can promote the sustainable development of agriculture.

Keywords: Difenoconazole, Non-point source pollution, In-situ bioelimination, Cleaner management