Did rhizobia associated with invading legumes escape bacteriophage enemies?

了解促进生物入侵的因素至关重要，因为它们威胁到宝贵的环境和经济资源。豆科植物中的许多植物都是入侵性杂草，这可能是因为它们与称为根瘤菌的细菌合作以获得可靠的氮供应。例如，豆科植物法国金雀花及其根瘤菌从欧洲传入美国后，已成为入侵性植物。引进的物种可能会因为逃避在家里困扰它们的敌人而成为入侵者。和其他细菌一样，根瘤菌也经常受到病毒的攻击。法国金雀花之所以入侵美国，是因为它的伙伴根瘤菌逃避了在美国困扰它们的病毒吗？为了开始回答这个问题，根瘤菌和相关病毒将从欧洲（本地）和美国（引进）的法国金雀花种群中收集。如果美国的法国扫帚根瘤菌种群逃脱了它们的敌人，它们应该被更少的病毒感染。然而，美国根瘤菌病毒可能已经进化到感染引入的根瘤菌。为了验证这一想法，将从一种本地豆科植物中收集根瘤菌和相关病毒，并对这些病毒进行测试，以发现它们是否能感染与法国金雀花相关的根瘤菌。这项工作将有助于理解病毒如何被用来操纵宿主种群。作为该项目的一部分，博士后学者将接受研究和交流技能的培训。为了解释根瘤菌及其伴侣豆科植物的入侵性，噬菌体必须在其家域控制根瘤菌种群，而不是在入侵范围内。 这种模式要求噬菌体是特化的，并且比异域根瘤菌更容易感染同域根瘤菌。作为解决这一问题的第一步，从三个欧洲和三个美洲的Genista monspessulana种群收集的根瘤菌噬菌体的宿主范围将在体外进行评估，接种到单一分离的“草坪”的慢生根瘤菌基因型分离自这些相同的人口。还将比较从天然和非天然范围种群分离的噬菌体数量。为了测试美国本土噬菌体是否可以控制引入的慢生根瘤菌种群，还将针对在上述调查中分离的慢生根瘤菌基因型测试从与本土豆科植物Lupinus arboreus相关的慢生根瘤菌分离的噬菌体的宿主范围。这项工作将测试敌人逃逸假说是否适用于与入侵豆类相关的经济和生态重要微生物。它将进一步研究噬菌体宿主范围如何响应宿主种群变化的变化而演变。通过这样做，它将提高对噬菌体如何影响宿主和有益细菌共生体之间互利相互作用的科学理解。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

It is crucial to understand the factors that promote biological invasions because they threaten valued environmental and economic resources. Many plants in the legume family are invasive weeds, perhaps because they cooperate with bacteria called rhizobia to obtain a reliable supply of nitrogen. For example, the legume French broom and its rhizobia have become invasive in America after being introduced from Europe. Introduced species might become invasive by escaping enemies that plague them at home. Like other bacteria, rhizobia are often attacked by viruses. Did French broom become invasive in America because its partner rhizobia escape viruses that plagued them back home? To begin answering this question, rhizobia and associated viruses will be collected from European (native) and American (introduced) populations of French broom. If American populations of French broom rhizobia have escaped their enemies, they should be infected by fewer viruses. However, American rhizobium viruses might have evolved to infect the introduced rhizobia. To test this idea, rhizobia and associated viruses will be collected from a native legume and the viruses will be tested to discover if they can infect rhizobia associated with French broom. This work will help understand how viruses could be used to manipulate host populations. A postdoctoral scholar will be trained in research and communication skills as part of this project.For release from bacteriophage infection to explain invasiveness of rhizobia and their partner legumes, bacteriophages must control rhizobium populations in their home range but not in the invasive range. This pattern requires that bacteriophages be specialized and more easily infect sympatric than allopatric rhizobia. As a first step toward addressing this issue, the host ranges of rhizobial bacteriophages collected from three European and three American populations of Genista monspessulana will be assessed in vitro by inoculation onto single-isolate "lawns" of Bradyrhizobium genotypes isolated from these same populations. The number of bacteriophages isolated from native and non-native range populations will also be compared. To test whether indigenous American bacteriophages might control introduced Bradyrhizobium populations, the host ranges of bacteriophages isolated from bradyrhizobia associating with the native legume, Lupinus arboreus, will also be tested against Bradyrhizobium genotypes isolated in the survey described above. This work will test whether the Enemy Escape Hypothesis applies to an economically and ecologically important microbe associated with an invasive legume. It will further examine how bacteriophage host ranges evolve in response to shifts in host population changes. In so doing, it will enhance scientific understanding of how bacteriophages affect mutualistic interactions between hosts and beneficial bacterial symbionts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.