Demethylation of the Antibiotic Methylarsenite is Coupled to Denitrification in Anoxic Paddy Soil
Demethylation of the Antibiotic Methylarsenite is Coupled to Denitrification in Anoxic Paddy Soil
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DOI：
10.1021/acs.est.1c04167
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发表时间：
2021-11-03
影响因子：
11.4
通讯作者：
Zhao, Fang-Jie
中科院分区：
文献类型：
--
作者：
Chen, Chuan;Shen, Yang;Zhao, Fang-Jie
砷的生物甲基化是砷地球化学循环的重要组成部分，其中间产物为甲基砷[MAs（III）]。它的高毒性被一些微生物用作抗生素来杀死其他微生物并获得竞争优势。一些好氧微生物已经进化出一种解毒机制，通过双加氧酶C-As裂解酶ArsI将MAs（III）脱甲基化。MAs（III）如何在缺氧条件下脱甲基尚不清楚。我们发现，硝酸盐除了一个淹水的水稻土增强MAs（III）的去甲基化。从土壤中分离的兼性厌氧芽孢杆菌CZDM 1能够在缺氧硝酸盐还原条件下使MAs（III）脱甲基。在菌株CZDM 1的基因组中鉴定出一个推定的C-As裂解酶基因（BcarsI）。BcarsI在As敏感的大肠杆菌AW 3110中的表达赋予细菌在缺氧硝酸盐还原条件下脱甲基化MAs（III）的能力，并增强其对MAs（III）的抗性。Bacillus sp. CZDM 1和E.大肠杆菌AW 3110在发酵条件下不能使MAs（III）脱甲基。五个保守的氨基酸残基的半胱氨酸，组氨酸和谷氨酸是必不可少的MAs（III）脱甲基缺氧硝酸盐还原条件下。推测的arsI基因广泛存在于细菌中，75%的测序基因组含有arsI，还具有异化硝酸还原酶基因narG或napA。这些结果揭示了一种新的机制，其中MAs（III）是通过砷脱甲基耦合到反硝化作用，这样的机制可能是常见的缺氧环境，如水稻土和湿地。
Arsenic (As) biomethylation is an important component of the As biogeochemical cycle, which produces methylarsenite [MAs(III)] as an intermediate product. Its high toxicity is used by some microbes as an antibiotic to kill off other microbes and gain a competitive advantage. Some aerobic microbes have evolved a detoxification mechanism to demethylate MAs(III) via the dioxygenase C-As lyase ArsI. How MAs(III) is demethylated under anoxic conditions is unclear. We found that nitrate addition to a flooded paddy soil enhanced MAs(III) demethylation. A facultative anaerobe Bacillus sp. CZDM1 isolated from the soil was able to demethylate MAs(III) under anoxic nitrate-reducing conditions. A putative C-As lyase gene (BcarsI) was identified in the genome of strain CZDM1. The expression of BcarsI in the As-sensitive Escherichia coli AW3110 conferred the bacterium the ability to demethylate MAs(III) under anoxic nitrate-reducing condition and enhanced its resistance to MAs(III). Both Bacillus sp. CZDM1 and E. coli AW3110 harboring BcarsI could not demethylate MAs(III) under fermentative conditions. Five conserved amino acid resides of cysteine, histidine, and glutamic acid are essential for MAs(III) demethylation under anoxic nitrate-reducing conditions. Putative arsI genes are widely present in denitrifying bacteria, with 75% of the sequenced genomes containing arsI, also possessing dissimilatory nitrate reductase genes narG or napA. These results reveal a novel mechanism in which MAs(III) is demethylated via ArsI by coupling to denitrification, and such a mechanism is likely to be common in an anoxic environment such as paddy soils and wetlands.