Carbon Monoxide Based Ecological Interactions Between Legumes and Their Rhizobial Symbionts

豆科植物为世界上约三分之一的人口提供重要的蛋白质来源。这些植物根部的固氮根瘤产生相对大量的一氧化碳。虽然CO在对流层化学和细胞生物学中发挥着重要的作用，但CO在豆科植物及其微生物共生体之间的生态相互作用中的作用却鲜为人知。初步结果表明，许多豆科植物共生体（包括农业上重要的固氮细菌菌株）对CO的利用可能促进其在土壤中的生存和活力。共生体的生存和生存能力反过来会影响植物的生产性能，并最终影响豆科植物在各种生态系统中的作用。为了验证这个概念，我们将使用成对的豆科共生体。每对中的一个菌株将被基因操纵以消除CO利用的能力。我们将分别在添加和不添加CO的混合种群中监测这些对中每个成员的相对和绝对存活率。我们还提出细菌CO氧化在一定程度上控制根瘤的净CO排放和整体植物性能。我们将用接种了CO氧化共生体或不氧化CO的突变体的豆科植物对这一概念进行测试。最后，我们将使用栽培方法和我们最近开发的分子工具来确定CO氧化根瘤菌在土壤中的分布与根和根瘤CO产量之间的关系。在温室和田间研究中，我们将重点关注散装土壤、根际和根面。为了扩大我们工作的影响，我们将把我们研究的适当方面纳入模块，这些模块将用于缅因州南布里斯托尔的一所K-8学校的科学教育课程。

Leguminous plants provide an important protein source for about one-third of the world's population. Nitrogen-fixing nodules on the roots of these plants produce relative large amounts of carbon monoxide (CO). Although CO plays important and well-known roles in the chemistry of the troposphere and in cellular biology, the roles of CO in ecological interactions between legumes and their microbial symbionts are poorly known. Preliminary results suggest that use of CO by many legume symbionts (including strains of agriculturally important nitrogen-fixing bacteria) may promote their survival and viability in soils. Symbiont survival and viability in turn can affect plant performance and ultimately impact the role of legumes in a variety of ecosystems. To test this concept, we will use pairs of legume symbionts. One strain in each pair will be manipulated genetically to eliminate the capacity for CO utilization. We will monitor relative and absolute survival of each member of these pairs singly and in mixed populations with and without added CO. We also propose that bacterial CO oxidation controls in part net CO emission by nodules and overall plant performance. We will test this notion using pairs of legumes inoculated with CO-oxidizing symbionts or mutants that do not oxidize CO. Finally, we will use cultivation methods and our recently developed molecular tools to determine relationships between the distribution of CO-oxidizing rhizobia in soil and root and nodule CO production. We will focus on bulk soil, the rhizosphere and the rhizoplane in greenhouse and field studies. In order to expand the impact of our work, we will incorporate appropriate aspects of our research into modules that will be used in science education programs at a K-8 school in South Bristol, Maine.