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

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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.