Regulation of nitrogen-fixation by different nitrogen sources in the marine non-heterocystous cyanobacterium Trichodesmium sp. NIBB1067 |
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Authors: | Kaori Ohki Jonathan P Zehr Paul G Falkowski Yoshihiko Fujita |
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Institution: | (1) Department of Cell Biology, National Institute for Basic Biology, 444 Okazaki, Aichi, Japan;(2) Marine Sciences Research Center, State University of New York, 11794-5000 Stony Brook, NY, USA;(3) Department of Applied Science, Brookhaven National Laboratory, 11973 Upton, NY, USA |
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Abstract: | The effect of various nitrogen sources on the synthesis and activity of nitrogenase was studied in the marine, non-heterocystous cyanobacterium Trichodesmium sp. NIBB1067 grown under defined culture conditions. Cells grown with N2 as the sole inorganic nitrogen source showed light-dependent nitrogenase activity (acetylene reduction). Nitrogenase activity in cells grown on N2 was not suppressed after 7 h incubation with 2 mM NaNO3 or 0.02 mM NH4Cl. However, after 3 h of exposure to 0.5 mM of urea, nitrogenase was inactivated. Cells grown in medium containing 2 mM NaNO3, 0.5 mM urea or 0.02 mM NH4Cl completely lacked the ability to reduce acetylene. Western immunoblots tested with polyclonal antisera against the Fe-protein and the Mo–Fe protein, revealed the following: (1) both the Fe-protein and the Mo–Fe protein were synthesized in cells grown with N2 as well as in cells grown with NaNO3 or low concentration of NH4Cl; (2) two bands (apparent molecular mass of 38 000 and 40 000) which cross-reacted with the antiserum to the Fe-protein, were found in nitrogen-fixing cells; (3) only one protein band, corresponding to the high molecular mass form of the Fe-protein, was found in cells grown with NaNO3 or low concentration of NH4Cl; (4) neither the Fe-protein nor the Mo–Fe protein was found in cells grown with urea; (5) the apparent molecular mass of the Fe-protein of Trichodesmium sp. NIBB1067 was about 5000 dalton higher than that of the heterocystous cyanobacterium, Anabaena cylindrica IAM-M1. |
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Keywords: | Cyanobacterium Trichodesmium Nitrogen-fixation Nitrogenase |
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