Community Structure and Activity of Ammonia-Oxidizing Bacteria In Aquatic Environments

9617690沃德硝化细菌在水生和陆地环境的氮循环中起着至关重要的作用。因此，控制硝化作用的环境变量，如氧气浓度和光照强度，最终会影响可利用氮素的化学性质和数量。水和沉积物中硝化作用的速率和分布可以通过反应/扩散模型从这些变量中进行关联和预测。然而，环境变量的影响转化为生物地球化学反应速率的机制取决于单个细菌对生理刺激的反应。用来测量氮循环转化率的同位素方法在灵敏度和精确度方面继续取得进展。同时，分子生态学的最新进展使检测和部分表征自然产生的硝化细菌组合的遗传多样性成为可能。沃德博士将研究两种水生环境中硝化细菌的组成和活性，这两种水生环境在环境变化的程度和规模上存在差异：远洋领域和潮间带沉积物生态系统。物种和群体特异的PCR扩增，然后DGGE筛选和测序扩增的核糖体和功能基因(氨单加氧酶，AMO)DNA片段将被用于1)定性描述不同环境中硝化细菌的组成和活性分布；2)确定物种组成和AMO活性随环境变量(如深度)和营养分布的变化的物理和时间尺度；3)研究物种组成、AMO表达和硝化速率之间的关系。这两个环境是氮素转化的重要环境，包含了广泛的环境变异性，从而可以阐明物种多样性、生境特征和生物地球化学转化速率之间的关系。

9617690 Ward Nitrifying bacteria play an essential role in the nitrogen cycle of aquatic and terrestrial environments. Environmental variables such as oxygen concentration and light intensity, which control nitrification, therefore ultimately influence the chemical nature and amount of nitrogen available. The rate and distribution of nitrification in water and sediments can be related to and predicted from these variables using reaction/diffusion models. However, the mechanisms by which the influence of environmental variables is translated into biogeochemical reaction rates depends on the response of individual bacteria to physiological stimuli. Advances continue to be made in sensitivity and precision in isotopic methods used to measure transformation rates in the nitrogen cycle. In parallel, recent advances in molecular ecology make it possible to detect and partially characterize the genetic diversity of naturally occurring nitrifying bacterial assemblages. Dr. Ward will investigate the composition and activity of nitrifying bacterial assemblages in two aquatic environments which differ in the degree and scale of environmental variability: a pelagic oceanic realm and an intertidal sediment ecosystem. Species and group-specific PCR amplification, followed by DGGE screening and sequencing of amplified ribosomal and functional gene (ammonia-mono-oxygenase, AMO) DNA fragments will be used to 1) describe qualitatively the composition and activity distributions of nitrifying bacteria in different environments; 2) determine the physical and temporal scales over which species composition and AMO activity vary in relation to environmental variables such as depth (with light and oxygen as important co-variables) and nutrient distributions; 3) investigate the relationship between species composition, AMO expression and nitrification rates. These two environments represent important ones for nitrogen transformations and include a wide range of environmental variability, so that the relationships among species diversity, habitat characteristics and biogeochemical transformation rates can be elucidated.