Ecology and Evolution of a Novel Symbiont Lineage: The Interaction of Burkholderia Bacteria with Neotropical legumes

豆科植物与根瘤菌（根瘤菌）之间的共生关系对人类福祉和自然生态系统都具有全球意义，因为它将氮气转化为氨，而氨通常是植物生产力的关键限制养分。然而，尽管经过了一个多世纪的深入研究，生物学家直到2001年才发现某些豆科植物使用伯克霍尔德菌属的根瘤菌，这种根瘤菌与所有其他已知的根瘤菌有着极其遥远的关系。该项目将分析来自巴拿马巴罗科罗拉多岛热带森林的伯克霍尔德氏菌菌株，以确定哪些豆科植物物种将伯克霍尔德氏菌作为结核细菌。它还将研究在该群落中与伯克霍尔德菌相关的豆科物种是否也在其地理范围的其他部分利用类似的伯克霍尔德菌菌株。最后，还将比较与伯克霍尔德菌和其他根瘤菌相互作用对植物的相对益处。该项目的主要价值在于，通过分析一组直到最近才被生物学家所知的共生细菌，它将提供对豆科植物-根瘤菌共生的更广泛的比较理解。许多伯克霍尔德菌种是重要的人类病原体或植物病原体，至少有一种伯克霍尔德菌共生菌的豆科宿主是严重的入侵杂草。因此，这项研究也将更好地了解该细菌属的基本生态学，特别是细菌病原体是否有可能进化成为有益的植物共生体（反之亦然）。这一信息对于评估这一细菌群对环境和人类健康的影响非常重要。

The symbiosis between legume plants and root nodule bacteria (rhizobia) is globally significant both to human welfare and to natural ecosystems, because it converts nitrogen gas to ammonia, which is often a key limiting nutrient for plant productivity. Yet despite more than a century of intensive study, biologists did not discover until 2001 that certain legume plants use nodule bacteria in the genus Burkholderia, which have an extremely distant relationship to all other known rhizobia. This project will analyze strains of Burkholderia from the tropical forest on Barro Colorado Island, Panama to determine which legume plant species use Burkholderia as nodule bacteria. It will also examine whether legume species that associate with Burkholderia in this community also utilize similar Burkholderia strains in other parts of their geographic range. Finally, it will also compare the relative benefits to plants of interacting with Burkholderia vs. other rhizobia. The main value of this project is that it will provide a broader comparative understanding of legume-rhizobial symbioses, by analyzing a group of symbiotic bacteria unknown to biologists until very recently. Many Burkholderia species are important human pathogens or plant pathogens, and at least one legume host of Burkholderia nodule symbionts is a serious invasive weed. Therefore, this research will also provide a better understanding of the basic ecology of this bacterial genus, especially, whether bacterial pathogens may potentially evolve to become beneficial plant symbionts (or vice versa). This information is important for evaluating the impact of this bacterial group on the environment and on human health.