Starter Grant: Diversity and Activity of Denitrifiers Across Estuarine Gradients

斯坦福大学的克里斯·弗朗西斯博士获得了一笔拨款，用于研究埃尔克霍恩斯劳的分布、多样性和反硝化细菌的活性如何受到环境梯度的影响。埃尔克霍恩斯劳是加州一个通往蒙特利湾的小河口。反硝化作用，即在厌氧条件下将硝酸盐和亚硝酸盐转化为气态产物（NO, N2O, N2），是将生态系统中的固定（可用）氮返回大气的主要生物过程。令人惊讶的是，人们对控制反硝化速率的已知环境因素（如硝酸盐、有机碳、氧等）如何影响反硝化微生物群落的多样性知之甚少。Elkhorn Slough包含了广泛的物理/化学梯度，是一个理想的自然系统，可以利用分子生物学（即基于dna的）和培养方法来解决这些问题。特别是编码亚硝酸盐还原酶的基因，该酶负责反硝化途径的关键步骤（NO2- - NO），将被用作表征河口沿岸四个地点收集的沉积物样品中反硝化细菌多样性的分子标记。为了收集目前几乎一无所知的新型河口反硝化菌，还将在Slough进行密集的培养研究。埃尔克霍恩沼泽是加利福尼亚州中部的一个主要湿地综合体，被认为是该州最重要的生态河口之一，其罕见的国家河口研究保护区（NERR）地位证明了这一点。在这个珍贵的河口，大约25-50%的外部氮输入通过反硝化去除，该项目将提供有关复杂环境梯度如何影响底层微生物群落的关键信息。由此收集的亚硝酸盐还原酶基因序列和河口反硝化物将为科学界提供宝贵的资源，并最终揭示对所有河口（和沿海）系统中这一生物地球化学重要过程的生态学和调控的见解。最后，该项目将有助于支持研究生的研究。

A grant has been awarded to Dr. Chris Francis of Stanford University to investigate how the distribution, diversity, and activity of denitrifying bacteria are influenced by environmental gradients in Elkhorn Slough, a small California estuary that opens into Monterey Bay. Denitrification, the transformation of nitrate and nitrite to gaseous products (NO, N2O, N2) under anaerobic conditions, is the main biological process responsible for returning fixed (usable) nitrogen from ecosystems to the atmosphere. Surprisingly, how environmental factors known to control denitrification rates (e.g., nitrate, organic carbon, oxygen, etc.) influence the diversity of denitrifying microbial communities is poorly understood. Elkhorn Slough, encompassing a wide range of physical/chemical gradients, is an ideal natural system in which to utilize both molecular biological (i.e., DNA-based) and cultivation approaches to address such questions. In particular, genes encoding nitrite reductase, the enzyme responsible for the key step of the denitrification pathway (NO2- - NO) will be used as a molecular marker to characterize the diversity of denitrifying bacteria in sediment samples collected at four sites along the estuary. In order to compile a culture collection of novel estuarine denitrifiers, for which virtually nothing is currently known, intensive cultivation studies will also be undertaken in the Slough. Elkhorn Slough is a principal wetland complex in central California and is considered one of the most ecologically important estuaries in the state, as evidenced by its rare National Estuarine Research Reserve (NERR) status. Roughly 25-50% of external nitrogen inputs are removed by denitrification in this treasured estuary, and this project will provide critical information regarding how the underlying microbial communities are influenced by complex environmental gradients. The resultant collections of nitrite reductase gene sequences and estuarine denitrifers will provide a valuable resource to the scientific community and, ultimately, reveal insights into the ecology and regulation of this biogeochemically-important process in all estuarine (and coastal) systems. Finally, this project will help support the research of graduate students.