Did rhizobia associated with invading legumes escape bacteriophage enemies?

了解促进生物入侵的因素是至关重要的，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杂草，也许是因为它们与一种叫做根瘤菌的细菌合作以获得可靠的氮供应。例如，豆科植物法国扫帚及其根瘤菌从欧洲传入美国后已成为入侵物种。引进的物种可能会通过逃避在国内困扰它们的敌人而成为入侵物种。像其他细菌一样，根瘤菌经常受到病毒的攻击。法国扫帚入侵美国是因为它的伙伴根瘤菌逃脱了在美国肆虐的病毒吗？为了开始回答这个问题，将从欧洲（本地）和美国（引进）的法国扫帚种群中收集根瘤菌和相关病毒。如果美国的法国扫帚根瘤菌逃脱了它们的敌人，它们感染的病毒应该更少。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扫帚有关的根瘤菌。这项工作将有助于了解病毒如何被用来操纵宿主种群。作为该项目的一部分，一名博士后学者将接受研究和沟通技巧方面的培训。为了从噬菌体感染中释放来解释根瘤菌及其伴侣豆科植物的侵袭性，噬菌体必须控制根瘤菌在其家乡范围内的数量，而不是在入侵范围内。这种模式要求噬菌体是特化的，比异源根瘤菌更容易感染同源根瘤菌。作为解决这一问题的第一步，从三个欧洲和三个美洲的monspessulana种群中收集的根瘤菌噬菌体的宿主范围将通过体外接种从这些种群中分离出的单株慢生根瘤菌基因型“草坪”来评估。还将比较从本地和非本地范围种群中分离的噬菌体的数量。为了测试美洲本土噬菌体是否可以控制引入的慢生根瘤菌种群，从与本土豆科植物Lupinus arboreus相关的慢生根瘤菌中分离的噬菌体的宿主范围也将对上述调查中分离的慢生根瘤菌基因型进行检测。这项工作将测试敌人逃跑假说是否适用于与入侵豆科植物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随着宿主种群变化的变化而进化。在这样做的过程中，它将加强对噬菌体如何影响宿主和有益细菌共生体之间相互作用的科学理解。该奖项反映了美国国家科学基金会的法定使命，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.