Science Opportunities offered by Mercury's Ice-Bearing Polar Deposits

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Abundances of Iron-Binding Photosynthetic and Nitrogen-Fixing Proteins of Trichodesmium Both in Culture and In Situ from the North Atlantic

Marine cyanobacteria of the genus Trichodesmium occur throughout the oligotrophic tropical and subtropical oceans, where they can dominate the diazotrophic community in regions with high inputs of the trace metal iron (Fe). Iron is necessary for the functionality of enzymes involved in the processes of both photosynthesis and nitrogen fixation. We combined laboratory and field-based quantifications of the absolute concentrations of key enzymes involved in both photosynthesis and nitrogen fixation to determine how Trichodesmium allocates resources to these processes. We determined that protein level responses of Trichodesmium to iron-starvation involve down-regulation of the nitrogen fixation apparatus. In contrast, the photosynthetic apparatus is largely maintained, although re-arrangements do occur, including accumulation of the iron-stress-induced chlorophyll-binding protein IsiA. Data from natural populations of Trichodesmium spp. collected in the North Atlantic demonstrated a protein profile similar to iron-starved Trichodesmium in culture, suggestive of acclimation towards a minimal iron requirement even within an oceanic region receiving a high iron-flux. Estimates of cellular metabolic iron requirements are consistent with the availability of this trace metal playing a major role in restricting the biomass and activity of Trichodesmium throughout much of the subtropical ocean

Isolement et caractérisation des champignons du sol halotolérant des Great Salt Plains de l'Oklahoma, USA

Les Great Salt Plains (GSP) de l\u27Oklahoma est un environnement hypersalin sur voie terrestre où les saumures saturées laissent des croûtes évaporites de NaCl. Le présent rapport examine la communauté fongique, en complément des rapports antérieurs sur les communautés bactériennes et archées. Vingt-cinq isolats fongiques du GSP sols ont été obtenus sur un milieu contenant 10 de NaCl et caractérisé. Basé sur l\u27analyse de la séquence du gène rRNA 18S, tous les isolats relèvent des ascomycètes, avec une prédominance de Trichocomaceae, représentée par les espèces de Aspergillus, Eurotium, et Penicillium. Les représentants de Anthrinium, Cladosporium, Debaryomyces, Fusarium, et Ulocladium ont également été isolés. Globalement les isolats étaient largement halotolérants, avec la meilleure croissance observée à des salinités inférieures et aucun halophilisme. Les genres fongiques observés étaient tous cosmopolites, sans une forte spécialisation. Pris ensemble, ces résultats appuient la conclusion que les zones hypersalines n\u27ont pas une communauté caractéristique, contrairement à ce qui a été observé à la GSP pour les bactéries et les archées.The Great Salt Plains (GSP) of Oklahoma is an inland terrestrial hypersaline environment where saturated brines leave evaporite crusts of NaCl. The current report examines the fungal community, complementing earlier reports on the bacterial and archaeal communities. Twenty-five fungal isolates from GSP soils were obtained on medium containing 10 NaCl and characterized. Based on 18S rRNA gene sequence analysis, all of the isolates fall within the ascomycetes, with a predominance of Trichocomaceae, represented by Aspergillus, Eurotium, and Penicillium species. Representatives of Anthrinium, Cladosporium, Debaryomyces, Fusarium, and Ulocladium also were isolated. Overall the isolates were widely halotolerant, with best growth observed at lower salinities and no halophilism. The fungal genera observed were all cosmopolitan, without strong specialization. Taken together, these results support the conclusion that hypersaline environments do not have a characteristic community, in contrast to what was observed at the GSP for bacteria and archaea.</p