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Oligotrophic oceanic waters of the central ocean gyres typically have extremely low dissolved fixed inorganic nitrogen concentrations, but few nitrogen-fixing microorganisms from the oceanic environment have been cultivated. Nitrogenase gene (nifH) sequences amplified directly from oceanic waters showed that the open ocean contains more diverse diazotrophic(More)
The Thermal Emission Spectrometer (TES) investigation on Mars Global Surveyor (MGS) is aimed at determining (1) the composition of surface minerals, rocks, and ices; (2) the temperature and dynamics of the atmosphere; (3) the properties of the atmospheric aerosols and clouds; (4) the nature of the polar regions; and (5) the thermophysical properties of the(More)
The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter has imaged the internal stratigraphy of the north polar layered deposits of Mars. Radar reflections within the deposits reveal a laterally continuous deposition of layers, which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly(More)
Year-round temperature measurements at 1600 m elevation during 1994 in the Asgard Range Antarctica, indicate that the mean annual frost point of the ice-cemented ground, 25 cm below the surface, is -21.7 +/- 0.2 degrees C and the mean annual frost point of the atmosphere is -27.5 +/- 1.0 degrees C. The corresponding mean annual temperatures are -24.9(More)
The diversity of nitrogenase genes in a marine cyanobacterial mat was investigated through amplification of a fragment of nifH, which encodes the Fe protein of the nitrogenase complex. The amplified nifH products were characterized by DNA sequencing and were compared with the sequences of nitrogenase genes from cultivated organisms. Phylogenetic analysis(More)
DNA sequences of a fragment of nifH from diverse cyanobacteria were amplified, cloned and sequenced to determine the evolutionary relationship of nitrogenase within the cyanobacteria as a group, and to provide a basis for the identification of uncultivated strains of cyanobacteria in the environment. Analysis of 30 nitrogenase DNA and deduced amino acid(More)
A modified nested reverse transcriptase PCR (RT-PCR) method was used to detect the expression of nitrogenase genes in meso-oligotrophic Lake George, New York. Net (>20-microm pore size) plankton samples collected from two sites (Dome Island and Hague Marina) were extracted for total RNA and genomic DNA to determine the identity of diazotrophic organisms(More)
A committee of the Mars Exploration Program Analysis Group (MEPAG) has reviewed and updated the description of Special Regions on Mars as places where terrestrial organisms might replicate (per the COSPAR Planetary Protection Policy). This review and update was conducted by an international team (SR-SAG2) drawn from both the biological science and Mars(More)
The availability of water-ice at the surface in the Mars polar cap and within the top meter of the high-latitude regolith raises the question of whether liquid water can exist there under some circumstances and possibly support the existence of biota. We examine the minimum temperatures at which liquid water can exist at ice grain-dust grain and ice(More)
Recent studies suggested that the daily cycle of nitrogen fixation activity in the marine filamentous nonheterocystous cyanobacterium Trichodesmium sp. is controlled by a circadian rhythm. In this study, we evaluated the rhythm of nitrogen fixation in Trichodesmium sp. strain IMS 101 by using the three criteria for an endogenous rhythm. Nitrogenase(More)