Role of ecological interactions on diversification of coexisting species in microbial communities

微生物群落--或生活在共享环境中的微生物群--发挥着支持地球上生命的基本功能，从元素在生态系统中的循环到消化复杂的食物。这些功能中的许多都依赖于令人难以置信的多样性微生物种群。了解是什么力量塑造了这种多样性，对于了解微生物群落如何发挥作用非常重要。对这些功能的全面了解最终将使科学家能够恢复生态系统并改善人类健康。虽然许多科学理论解释了为什么会存在这样的微生物多样性，但科学家目前几乎没有实验证据。该项目将通过观察一种被称为进化分支的现象来提供这一缺失的证据，在这种现象中，一个祖先的微生物种群分裂成两个后代种群。这项实验将测试一种新的想法，即一个物种与另一个物种之间的营养交换如何导致两种不同的进化策略，从而使生长最大化。一种策略包括游向其他物种泄漏的营养物质，并在其他物种之前消耗资源。另一种策略是不移动和节省游泳所需的能量。随着时间的推移，这两种策略可以将种群置于不同的轨道上，并最终导致新物种的创造。该项目还将开发维护实验系统的技术，这将有助于其他科学家群体研究微生物物种多样性的起源。这项研究的第三个影响是提供机会，增加未被充分代表的群体对科学的参与。最后，为了向公众传播微生物研究的重要性，研究人员将与科学教育实习生合作，实施一项关于微生物生物多样性对生态系统功能和气候变化的影响的中学课程。在共生互动中，一个物种受益，另一个物种不受影响。研究人员将在实验上确定共生相互作用在微生物群落中新细菌物种形成中的作用。他们将以共生关系培养细菌：产生代谢副产品的不动杆菌和消耗该副产品的假单胞菌。使用这些培养物，他们将(1)通过在实验室条件下进化1000代人的共生性来评估促进假单胞菌谱系分化的条件；(2)表征适应度权衡并测试对不同谱系的频率依赖选择；以及(3)通过跟踪种群中适应性突变的命运来评估共同进化和分歧。为了实现这一目标，研究人员将采用实验进化、生理分析、全基因组和种群测序以及相互入侵实验的组合。这项研究将提供对共同进化环境中微生物物种形成的异常全面的表征。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Microbial communities — or groups of microorganisms that live in a shared environment — perform essential functions that support life on earth, from the cycling of elements through ecosystems to digesting complex foods. Many of these functions rely on an incredibly diverse pool of microbial species. Understanding what forces have shaped this diversity is important to understand how microbial communities function. A complete understanding of these functions would ultimately allow scientists to restore ecosystems and improve human health. While many scientific theories explain why such microbial diversity exists, scientists currently have little experimental evidence. The project will provide this missing evidence by looking at a phenomenon known as evolutionary branching, in which an ancestral microbial population splits into two descendant populations. The experiment will test a new idea about how the exchange of nutrients from one species to another can lead to two different evolutionary strategies that maximize growth. One strategy involves swimming toward the nutrients leaked by the other species and consuming the resources before others do. The other strategy is not to move and save the energy that would otherwise be required for swimming. Over time, these two strategies can set populations onto different trajectories and eventually lead to the creation of new species. The project will also develop techniques to maintain an experimental system, which will help other groups of scientists study the origins of microbial species diversity. A third impact of the research is to provide opportunities to increase the participation of underrepresented groups in science. Finally, to disseminate the importance of microbial research to a public audience, the researchers will work with science-education interns to implement a middle school curriculum on the impacts of microbial biodiversity on ecosystem functioning and climate change.In commensal interactions, one species benefits while the other is unaffected. The researchers will experimentally determine the role of commensal interactions in the formation of new bacterial species in microbial communities. They will culture bacteria in a commensal relationship: Acinetobacter, which produces a metabolic by-product, and Pseudomonas, which can consume that by-product. Using these cultures, they will (1) assess the conditions promoting divergence of Pseudomonas lineages by evolving the commensalism under lab conditions over 1000 generations; (2) characterize fitness tradeoffs and test frequency-dependent selection for divergent lineages; and (3) assess coevolution and divergence by tracking the fate of adaptive mutations in populations. To achieve this, the researchers will employ a combination of experimental evolution, physiological assays, whole genomes and population sequencing, and reciprocal invasion experiments. The research will provide an exceptionally comprehensive characterization of microbial speciation in a coevolutionary context.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.