Phytoremediation by Reduction of Toxic Metal Ions

在世界许多地区，9513347兆赫的重金属污染已达到有毒水平，已成为一个紧迫的问题。我们的长期目标是识别和利用单基因特征，以植物修复为基础，实现对金属离子污染的生态无害解决方案。细菌MERA基因的项目，汞离子还原酶(MERA)，将离子汞，汞++的解毒作用编目，将其还原为毒性较低的金属形式Hg0。最近的研究表明，高度突变的MERA基因merApe9在转基因拟南芥中具有显著的抗Hg++能力。转基因种子萌发，幼苗生长，植物开花，并在含有高达100um Hg++(20ppm)的介质上结实，而对照幼苗在25um的萌发过程中或萌发后不久死亡。在这个过程中，这些植物进化出了大量的HGO。抗性最强的植物品系在汞离子未受挑战的对照植物上也能生长，实际上需要汞才能最适生长。转基因植株还表现出对介质中Au+毒性水平的抗性。该项目的近期目标是探索金属离子还原作为一种植物修复多种重金属污染物的方法。初步证据表明，除Hg++外，Mera PE9还能降低大肠杆菌中Au+和Cu2++的含量。MERA属于一个不同的序列相关还原酶家族，除了识别汞++外，它还识别各种有机和硫醇底物。除Hg++外，Mera还结合了Ag+、Cu++、Cd++和Au+。因此，可以假设：MERA基因可以突变来指导多种金属离子的有效还原，以用于修复或提取。该提议的具体目标是产生具有新的底物特异性的MERA突变体(例如，增强汞++的还原以及新的铜、铅和镉的还原)。在未来，转基因构建物将在模式植物中进行检验，以期在金属离子污染的植物修复中得到潜在的应用。

9513347 Meagher Heavy metal contamination has reached toxic levels in many parts of the world and has become an urgent problem. Our long term goal is to identify and utilize single gene traits to effect ecologically sound solutions to metal ion contamination based on phytoremediation. The project of the bacterial merA gene, mercuric ion reductase (MerA), catalzes the detoxification of ionic mercury, Hg++, reducing it to its less toxic metallic form, Hg0. Recently it has been shown that a highly mutagenized merA gene, merApe9, confers remarkable levels of resistance to Hg++ in transgenic Arabidopsis plants. Transgenic seeds germinate, seedlings grow, and plants flower and set seed on media containing up to 100 uM Hg++ (20 ppm), while control seedlings die during or shortly after germination at 25 uM. These plants evolved significant levels of Hgo in the process. The most resistant plant lines grow as well on Hg++ as unchallenged control plants and acturally require mercury for optimum growth. The transgenic plants also show resistance to toxic levels of Au+++ in media. The immediate goal of this project is to explore metal ion reduction as a method of phytoremediation for a variety of heavy metal pollutants. Preliminary evidence is presented to suggest that besides Hg++ merA pe9 also can reduce Au+++ and Cu++ in E. coli. MerA belongs to a diverse family of sequence-related reductases, which recognize a wide variety of organic and thiol substrates in addition to Hg++. Besides Hg++ MerA already binds Ag+, Cu++, Cd++, and Au+++. Therefore, it is hypothesized that: the merA gene can be mutated to direct the efficient reduction of a wide variety of metal ions for remediation or extraction. The specific aim of the proposal is to generate merA mutants with novel substrate specificities (e.g., enhanced reduction of Hg++ and novel reduction of Cu++, Pb++, and Cd++). In the future transgenic constructs will be examined in model plants for their potential use in the phytoremediation of metal ion pollution.