Delong 9418442 Archaebacteria are an evolutionarily distinct group of prokaryotes. Until very recently, archaebacteria were thought to thrive only in a few disparate niches, consisting of either very hot, very salty, or strictly anaerobic environments. Recent studies show that pelagic marine archaebacteria can constitute a major fraction (>30%) of Antarctic prokaryote biomass in coastal waters off Palmer Station, Antarctica. Since surface waters off Palmer Station have yielded the highest biomass estimates of pelagic archaebacteria to date, this area is uniquely suited for studing these unusual microorganisms. The main objective of the proposed work is to characterize the ecological significance, distribution and aboundance, and the metabolic and physiological activities, of pelagic marine archaebacteria in coastal waters off Anvers Island, Antarctica. Molecular biological techniques will be used to quantify the spatial and temporal abundance and variability of Antarctic marine archaebacterial species. Highly sensitive, semiautomated methods will be developed to quantify archaebacterial group and species-specific ribosomal RNA and DNA in field samples. To better understand their physiological activities, methods employing "kingdom-specific" metabolic inhibitors will be used to estimate the contribution of pelagic archaebacteria to total prokaryotic heterotrophic activity. The project will provide information on the seasonal and spatial variability of pelagic Antarctic archaebacteria, which can comprise a major fraction of Antarctic coastal prokarytoic biomass. Finally, this project will also enhance understanding of the biogeochemical activities and ecological roles of these abundant "archaeoplankton" in coastal Antarctic waters, and may provide clues as to their specific adaptations to the unique Antarctic environment.
