SGER: Molecular Identification of Functionally Significant Nitrogen Fixing Bacteria

[00:84526]所有生态系统都依赖于微生物群落的养分供应和再生。这些群落被认为对环境条件的变化、物种多样性的变化和/或响应环境变化的活动水平非常敏感。重要的环境功能可以维持，因为微生物群落在每个主要功能群中包含足够的物种多样性（即功能冗余）以抵消物种损失。然而，在一些研究中已经观察到与群落结构变化相关的功能急剧下降。自然微生物群落的可塑性，特别是在植被土壤和沉积物等物理结构环境中的可塑性，以及微生物多样性与生态功能之间的联系显然还没有得到很好的理解。阻碍这一领域进展的一个主要障碍是，我们无法确定在给定的功能群（如固氮细菌）中，哪些物种实际上发挥了有问题的重要功能。在这个SGER项目中，研究者将直接从米草属植物的根和根际样品中提取编码nifH基因产物——氮酶铁蛋白的信使RNA，将mRNA序列转化为双链DNA，并确定这些复制DNA分子的核苷酸序列。这些序列将与直接从米草属沼泽中固氮生物的现有DNA提取物中提取的序列进行比较，以确定哪些物种在积极地固定氮。将确定功能优势物种对实验操作和环境条件季节性变化的反应，以直接评估功能冗余对维持生态上重要的固氮过程的重要性。这项研究将是第一个将关键微生物功能群的环境功能直接与负责该功能的物种联系起来的研究之一。这里采用的方法将广泛适用于理解微生物多样性在功能背景下的重要性，并将提供功能冗余对复杂自然环境中自然细菌组合的重要性的第一次直接检查之一。

0084526LovellAll ecosystems are dependent on nutrient supply and regeneration by microbial communities. These communities are thought to be very sensitive to variations in environmental conditions, changing species diversity and/or activity levels in response to environmental changes. Important environmental functions may be maintained since microbial communities contain a sufficient diversity of species in each major functional group (i.e. functional redundancy) to negate species losses. However, dramatic decreases in function that are correlated with changes in community structure have been observed in some studies. The plasticity of natural microbial communities, particularly in physically structured environments such as vegetated soils and sediments, and the connections between microbial diversity and ecological function are clearly not well understood. A major hurdle impeding progress in this area has been our inability to determine which species within a given functional group (such as the nitrogen fixing bacteria) are actually performing the vital function in question. In this SGER project the investigators will extract messenger RNA encoding the nifH gene product, the nitrogenase iron protein, directly from Spartina root and rhizosphere samples, convert the mRNA sequences to double stranded DNA, and determine the nucleotide sequences of these copy DNA molecules. These sequences will be compared to those recovered directly from existing DNA extracts of nitrogen fixers in a Spartina marsh, to identify which of the many species are actively fixing nitrogen. The responses of the functionally dominant species to experimental manipulations and to seasonal changes in environmental conditions will be determined, to directly assess the importance of functional redundancy to maintenance of the ecologically important process of nitrogen fixation. This study will be among the first to link the environmental function of a key microbial functional group directly to the species responsible for this function. The approach taken here will be broadly applicable to understanding the significance of microbial diversity in a functional context and will provide one of the first direct examinations of the significance of functional redundancy for a natural bacterial assemblage in a complex, natural environment.