Abstract
Phoxim, a type of organophosphorus pesticide (OP), is widely used in both agriculture and fisheries. The persistence of phoxim has caused serious environmental pollution problems. In this study, Bacillus amyloliquefaciens YP6 (YP6), which is capable of promoting plant growth and degrading broad-spectrum OPs, was used to study phoxim degradation. Different culture media were applied to evaluate the growth and phoxim degradation of YP6. YP6 can grow rapidly and degrade phoxim efficiently in Luria–Bertani broth (LB broth) medium. Furthermore, it can also utilize phoxim as the sole phosphorus source in a mineral salt medium. Response surface methodology was performed to optimize the degradation conditions of phoxim by YP6 in LB broth medium. The optimum biodegradation conditions were 40 °C, pH 7.20, and an inoculum size of 4.17% (v/v). The phoxim metabolites, O,O-diethylthiophosphoric ester, phoxom, and α-cyanobenzylideneaminooxy phosphonic acid, were confirmed by liquid chromatography–mass spectrometry. Meanwhile, transcriptome analysis and qRT-PCR were performed to give insight into the phoxim-stress response at the transcriptome level. The hydrolase-, oxidase-, and NADPH-cytochrome P450 reductase-encoding genes were significantly upregulated for phoxim hydrolysis, sulfoxidation, and o-dealkylation. Furthermore, the phoxim biodegradation pathways by YP6 were proposed, for the first time, based on transcriptomic data and product analysis.
Highlights
Phoxim (O,O-diethyl O-(alpha-cyanobenzylideneamino) phosphorothioate), a type of organophosphorus pesticide (OP), is widely used in both agriculture and fisheries to control a variety of unwanted insects and underground pests via dipping, spraying, or pour-on applications [1]
Our preliminary results indicated that strain YP6 possessed plant growth-promoting ability [22] and could efficiently degrade a wide range of OPs, including phoxim [23,24]
To study further the growth and phoxim degradation of strain YP6 in LB broth and M-2 liquid medium, samples were taken at different times for analysis
Summary
Phoxim (O,O-diethyl O-(alpha-cyanobenzylideneamino) phosphorothioate), a type of organophosphorus pesticide (OP), is widely used in both agriculture and fisheries to control a variety of unwanted insects and underground pests via dipping, spraying, or pour-on applications [1]. Many microorganisms that efficiently degrade phoxim have been successfully isolated [9,10,11,12,13,14,15]. Among these phoxim-degrading bacteria, the genus Bacillus has a sporulation capacity that enables them to survive in adverse environmental conditions [16,17]. Some studies have investigated the degradation of OPs by Bacillus members [19,20,21], but few have focused on the factors affecting OP degradation and the degradation mechanism. Exploring the factors affecting OP degradation and the degradation mechanism can provide a theoretical basis for environmental remediation
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