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首页> 外文期刊>Applied Microbiology >The Two-Component Monooxygenase MeaXY Initiates the Downstream Pathway of Chloroacetanilide Herbicide Catabolism in Sphingomonads
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The Two-Component Monooxygenase MeaXY Initiates the Downstream Pathway of Chloroacetanilide Herbicide Catabolism in Sphingomonads

机译：两组分单加氧酶MeaXY引发Sphingomonads中的氯乙酰苯胺除草剂分解代谢的下游途径。

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Due to the extensive use of chloroacetanilide herbicides over the past 60 years, bacteria have evolved catabolic pathways to mineralize these compounds. In the upstream catabolic pathway, chloroacetanilide herbicides are transformed into the two common metabolites 2-methyl-6-ethylaniline (MEA) and 2,6-diethylaniline (DEA) through N-dealkylation and amide hydrolysis. The pathway downstream of MEA is initiated by the hydroxylation of aromatic rings, followed by its conversion to a substrate for ring cleavage after several steps. Most of the key genes in the pathway have been identified. However, the genes involved in the initial hydroxylation step of MEA are still unknown. As a special aniline derivative, MEA cannot be transformed by the aniline dioxygenases that have been characterized. Sphingobium baderi DE-13 can completely degrade MEA and use it as a sole carbon source for growth. In this work, an MEA degradation-deficient mutant of S. baderi DE-13 was isolated. MEA catabolism genes were predicted through comparative genomic analysis. The results of genetic complementation and heterologous expression demonstrated that the products of meaX and meaY are responsible for the initial step of MEA degradation in S. baderi DE-13. MeaXY is a two-component flavoprotein monooxygenase system that catalyzes the hydroxylation of MEA and DEA using NADH and flavin mononucleotide (FMN) as cofactors. Nuclear magnetic resonance (NMR) analysis confirmed that MeaXY hydroxylates MEA and DEA at the para-position. Transcription of meaX was enhanced remarkably upon induction of MEA or DEA in S. baderi DE-13. Additionally, meaX and meaY were highly conserved among other MEA-degrading sphingomonads. This study fills a gap in our knowledge of the biochemical pathway that carries out mineralization of chloroacetanilide herbicides in sphingomonads.IMPORTANCE Much attention has been paid to the environmental fate of chloroacetanilide herbicides used for the past 60 years. Microbial degradation is considered an important mechanism in the degradation of these compounds. Bacterial degradation of chloroacetanilide herbicides has been investigated in many recent studies. Pure cultures or consortia able to mineralize these herbicides have been obtained. The catabolic pathway has been proposed, and most key genes involved have been identified. However, the genes responsible for the initiation step (from MEA to hydroxylated MEA or from DEA to hydroxylated DEA) of the downstream pathway have not been reported. The present study demonstrates that a two-component flavin-dependent monooxygenase system, MeaXY, catalyzes the para-hydroxylation of MEA or DEA in sphingomonads. Therefore, this work finds a missing link in the biochemical pathway that carries out the mineralization of chloroacetanilide herbicides in sphingomonads. Additionally, the results expand our understanding of the degradation of a special kind of aniline derivative.
机译：由于在过去60年中广泛使用了氯乙酰苯胺除草剂，细菌已经进化出分解代谢途径来使这些化合物矿化。在上游分解代谢途径中，氯乙苯胺除草剂通过N-脱烷基化和酰胺水解转化为两种常见的代谢物2-甲基-6-乙基苯胺（MEA）和2,6-二乙基苯胺（DEA）。 MEA下游的途径是由芳环的羟基化作用引发的，然后经过几步反应，其转化为用于环裂解的底物。该途径中的大多数关键基因已被鉴定。然而，涉及MEA的初始羟基化步骤的基因仍是未知的。作为一种特殊的苯胺衍生物，MEA无法被已表征的苯胺双加氧酶转化。巴氏鞘氨醇DE-13可以完全降解MEA，并将其用作生长的唯一碳源。在这项工作中，分离出一种MEA降解缺陷的巴氏链球菌DE-13突变体。通过比较基因组分析预测了MEA分解代谢基因。遗传互补和异源表达的结果表明，meaX和meaY的产物是造成巴德链霉菌DE-13中MEA降解的起始步骤。 MeaXY是一种两组分的黄素蛋白单加氧酶系统，使用NADH和黄素单核苷酸（FMN）作为辅因子，催化MEA和DEA的羟基化。核磁共振（NMR）分析证实MeaXY在对位羟基化MEA和DEA。当在巴氏链霉菌DE-13中诱导MEA或DEA时，meaX的转录显着增强。此外，在其他降解MEA的鞘氨醇单胞菌中，meaX和meaY高度保守。这项研究填补了我们对鞘氨醇中氯乙酰苯胺除草剂矿化的生化途径知识的空白。重要信息在过去的60年中，人们对氯乙酰苯胺除草剂的环境命运给予了很多关注。微生物降解被认为是这些化合物降解的重要机制。最近的许多研究都对氯乙酰苯胺除草剂的细菌降解进行了研究。已经获得了能够使这些除草剂矿化的纯培养物或财团。已经提出了分解代谢途径，并且已经鉴定了涉及的大多数关键基因。但是，尚未报道负责下游途径的起始步骤（从MEA到羟基化MEA或从DEA到羟基化DEA）的基因。本研究表明，两组分黄素依赖性单加氧酶系统MeaXY可以催化鞘氨醇中MEA或DEA的对羟基化。因此，这项工作在进行鞘氨醇中氯乙酰苯胺除草剂矿化的生化途径中发现了一个缺失的环节。此外，结果扩大了我们对特殊种类苯胺衍生物降解的理解。

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