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项拨款，用于研究埃尔克霍恩斯劳的环境梯度如何影响反硝化细菌的分布、多样性和活动。埃尔克霍恩斯劳是加利福尼亚州的一个小河口，通向蒙特利湾。反硝化作用是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)的过程，是将固定(可用)氮从生态系统返回大气的主要生物过程。令人惊讶的是，已知的环境因素如何控制反硝化速率(例如，硝酸盐、有机碳、氧气等)。对反硝化微生物群落多样性的影响知之甚少。Elkhorn Slough包含了广泛的物理/化学梯度，是利用分子生物学(即基于DNA)和栽培方法来解决这些问题的理想自然系统。特别是，负责反硝化途径关键步骤(NO2--NO)的亚硝酸还原酶编码基因将被用作分子标记，以表征在河口沿岸四个地点采集的沉积物样本中反硝化细菌的多样性。为了汇编目前几乎一无所知的新型河口反硝化细菌的培养集合，还将在斯劳夫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)地位就是明证。在这个珍贵的河口，大约25%-50%的外部氮输入通过反硝化作用被去除，这个项目将提供关于基础微生物群落如何受到复杂环境梯度影响的关键信息。由此收集的亚硝酸还原酶基因序列和河口反硝化细菌将为科学界提供宝贵的资源，并最终揭示这一在所有河口(和沿海)系统中具有生物地球化学重要性的过程的生态和调节。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.