Studies of Degradation of Xenobiotic Compound: A Window on the Evolution of a Novel Metabolic Pathway at an Early Stage of Development

该项目将研究五氯苯酚在土壤细菌Sphingomonashlorophenolica中降解途径的演变。 由于五氯苯酚是在1936年才引入的，因此这一途径一定是最近才在微生物中进化和组装的。这个实验系统提供了一个不寻常的机会，在其发展的非常早期阶段研究代谢途径。 这一途径的出现也特别令人感兴趣，因为五氯苯酚毒性很强，而且具有异生物质性，因此是一个特别具有挑战性的降解目标。先前的工作表明，四氯氢醌脱卤酶，在途径中的第二种酶，可能起源于谷胱甘肽依赖性双键异构酶，如马来酰乙酰乙酸异构酶或马来酰丙酮酸异构酶（酶参与酪氨酸和苯甲酸的降解，分别）。 该项目的第一个目标是进一步探索这种酶的起源。 将测量几种马来酰乙酰乙酸酯和马来酰丙酮酸异构酶中的脱卤酶活性水平，以评估该酶被募集用作脱卤酶的假设，因为它偶然具有低但有用的脱卤酶活性水平。该项目的第二个目标是调查脱卤酶基因的遗传背景，以确定它是否起源于S. chlorophenolica或通过水平转移从另一种生物引入。 该项目旨在研究土壤细菌进化新的代谢途径以降解最近因农业，工业，军事或家庭用途而引入环境中的人为污染物的机制。 这些污染物往往难以生物降解，因此在环境中持续存在。 细菌进化出降解人为化合物的新途径的能力是影响这些化合物的环境命运的关键因素。 该项目涉及在一种称为Sphingomonashlorophenolica的土壤细菌中降解五氯苯酚（一种广泛使用的高毒性木材防腐剂）的新代谢途径的演变。这种细菌显然通过招募细胞中已经存在的蛋白质来执行新的功能，从而进化出了一条新的途径。 本项目将研究其中一种酶-四氯氢醌脱卤酶的进化起源。

This project will address the evolution of the pathway for degradation of pentachlorophenol (PCP) in the soil bacterium Sphingomonas chlorophenolica. Since PCP was introduced only in 1936, this pathway must have evolved and assembled rather recently in microorganisms. This experimental system provides an unusual opportunity to study a metabolic pathway at a very early stage in its development. The emergence of this pathway is also of special interest because PCP is highly toxic, as well as being xenobiotic, and is thus a particularly challenging target for degradation. Previous work has suggested that tetrachlorohydroquinone dehalogenase, the second enzyme in the pathway, may have originated from a glutathione-dependent double bond isomerase such as maleylacetoacetate isomerase or maleylpyruvate isomerase (enzymes involved in degradation of tyrosine and benzoate, respectively). The first objective of the project is to further explore the origin of this enzyme. Levels of dehalogenase activity in several maleylacetoacetate and maleylpyruvate isomerases will be measured in order to evaluate the hypothesis that this enzyme was recruited to serve as a dehalogenase because it fortuitously had a low but useful level of dehalogenase activity. The second objective of the project is to investigate the genetic context of the dehalogenase gene in order to determine whether itoriginated from a gene duplication event in S. chlorophenolica or was introduced by horizontal transfer from another organism. This project addresses the mechanisms by which soil bacteria evolve new metabolic pathways to degrade anthropogenic pollutants which have been recently introduced into the environment as a result of agricultural, industrial, military, or household uses. Such pollutants are often resistant to biodegradation and consequently persist in the environment. The ability of bacteria to evolve new pathways to degrade anthropogenic compounds is a critical factor that affects the environmental fate of these compounds. This project concerns the evolution of a new metabolic pathway for degradation of pentachlorophenol, a widely used and highly toxic wood preservative, in a soil bacterium called Sphingomonas chlorophenolica. This bacterium has apparently evolved a new pathway by recruiting proteins already present in the cell to perform new functions. The evolutionary origin of one of these enzymes, tetrachlorohydroquinone dehalogenase, will be studied during this project.