Ongoing functional evolution of the bacterial atrazine chlorohydrolase AtzA
Ongoing functional evolution of the bacterial atrazine chlorohydrolase AtzA
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DOI：
10.1007/s10532-013-9637-2
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发表时间：
2014-02
期刊：
影响因子：
3.6
通讯作者：
Sajid A. Noor;F. Changey;J. Oakeshott;C. Scott;F. Martin-Laurent
中科院分区：
文献类型：
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作者：
Sajid A. Noor;F. Changey;J. Oakeshott;C. Scott;F. Martin-Laurent
世纪后半期大量使用的阿特拉津、西玛津等三嗪类除草剂为土壤微生物提供了丰富的新氮源。20世纪90年代中期，从不同地点的各种土壤细菌中分离出对阿特拉津和西玛津都有活性的AnatzAdechlorinase。我们调查了2000年从反复暴露于三嗪的法国农业土壤中分离出的八株三嗪降解菌的theatzA基因。与原始分离物相比，在A.食氨菌菌株特别是其中三个（V92L，A170T和A296T）是从大多数分离株中回收的，并且来自相隔长达900 km的位置，因此可能反映了新功能的持续选择。后者中的两个（A170 T和A296 T）确实被发现赋予更高的特异性西玛津，虽然不是阿特拉津，和更大的亲和力所需的金属离子的活动，比原来的变体。相比之下，我们发现，在实验室培养中，在含有高浓度阿特拉津的培养基中持续维持含有originalatzA的分离株12年，导致另一种氨基酸取代的固定，这大大降低了三嗪的活性。培养基中高浓度的阿特拉津可能放松了对高效三嗪脱氯酶活性的选择，并且在这些条件下存在一些尚未表征的针对该酶活性的反选择。
Triazine herbicides such as atrazine and simazine which were heavily used in the latter half of the twentieth century constituted a rich new source of nitrogen for soil microbes. AnatzAdechlorinase active against both atrazine and simazine was isolated from various soil bacteria from diverse locations in the mid 1990s. We have surveyed theatzAgenes from eight triazine-degradingAminobacter aminovoransstrains isolated from French agricultural soils recurrently exposed to triazines in 2000. Six amino acid differences from the original isolate were each found in more than one of theA. aminovoransstrains. Three of these in particular (V92L, A170T and A296T) were recovered from a majority of the isolates and from locations separated by up to 900 km, so may reflect ongoing selection for the new function. Two of the latter (A170T and A296T) were indeed found to confer higher specificity for simazine, albeit not atrazine, and greater affinity for a metal ion required for activity, than did the original variant. In contrast, we found that ongoing maintenance of the originalatzA-containing isolate in laboratory culture for 12 years in a medium containing high concentrations of atrazine has led to the fixation of another amino acid substitution that substantially reduces activity for the triazines. The high concentrations of atrazine in the medium may have relaxed the selection for a highly efficient triazine dechlorinase activity, and that there is some, as yet uncharacterised, counter selection against the activity of this enzyme under these conditions.