Evolution of Copper Resistance in Plant Microbes

这项拟议的研究是为了调查植物相关细菌如何适应环境中铜的有毒水平。铜是一种重要的杀菌剂，经常用于农业植物的疾病控制，因此与这些植物相关的微生物会定期接触到高水平的这种金属。植物病原细菌对铜的抗性发展可能会对未来铜在植物病害防治中的应用构成威胁，而更好地了解这种抗性是如何发展的对于评估这种威胁将是重要的。此外，了解植物微生物如何产生对铜的抵抗力，可能有助于设计对受污染废水中的铜进行解毒的方法，或用于对植物和有益微生物进行基因改造，以提高农业环境中对铜的耐受性。微生物对汞等有毒金属的耐受性已被广泛研究，但铜的耐受性受到的关注要少得多。与其他许多重餐不同，生物有机体需要铜作为某些酶的组成部分；低水平的铜是有益的，但高水平的铜是有毒的。因此，微生物种群中铜抗性的演变必须涉及防止铜毒性的机制和维持足够铜以供细胞生长的能力之间的平衡。库克西博士从一个农业系统中分离出了耐铜细菌，在这个系统中，铜化合物经常用于植物中，以控制细菌疾病。编码铜抗性的基因已被克隆和鉴定。这一建议涉及克隆基因的生化功能，它们的遗传调节，以及它们与最近在几个细菌物种中发现的同源基因的关系。库克西博士假设，抗铜基因是从产生正常含铜蛋白的基因进化而来的。这些蛋白质可能已经被修饰，以结合更多的铜，并防止有毒金属在细菌细胞内的溶液中达到高浓度。然而，由于铜是生长所必需的，只有当铜的毒性水平存在时，抗性基因才应该表达；库克西博士已经证明，铜诱导抗性基因是可以诱导的，这一建议解决了铜诱导基因表达的基本机制。

The proposed research is to investigate how plant-associated bacteria adapt to toxic levels of copper in the environment. Copper is an important bactericide used frequently for disease control on agricultural plants, and microbes associated with those plants are therefore exposed periodically to high levels of this metal. The development of copper resistance in plant pathogenic bacteria may pose a threat to the future use of copper in plant disease control, and a better understanding of how this resistance develops will be important for evaluating this threat. In addition, knowledge of how plant microbes develop copper resistance may be useful in designing methods for detoxifying copper in contaminated wastewaters or for genetically modifying plants and beneficial microbes for increased tolerance to copper in the agricultural environment. Microbial resistance to toxic metals such as mercury has been studied extensively, but copper resistance has received much less attention. Unlike many other heavy meals, copper is required by living organisms as a component of certain enzymes; at low levels it is beneficial, but at high levels it is toxic. The evolution of copper resistance in microbial populations must therefore involve a balance between mechanisms to prevent copper toxicity and the ability to maintain enough copper for cell growth. Dr. Cooksey isolated copper-resistant bacteria from an agricultural system where copper compounds are routinely applied to plants for bacterial disease control. Genes encoding copper resistance have been cloned and characterized. This proposal concerns the biochemical function of the cloned genes, their genetic regulation, and their relationship to homologous genes that have recently been detected in several bacterial species. Dr. Cooksey has hypothesized that the copper resistance genes have evolved from genes that produce normal copper-containing proteins. These proteins may have been modified to bind more copper and prevent the toxic metal from reaching high concentrations in solution inside the bacterial cell. Since copper is essential for growth, however, the resistance genes should be expressed only when toxic levels of copper are present; Dr. Cooksey has shown that the resistance genes are copper- inducible, and this proposal addresses basic mechanisms of copper-inducible gene expression.