title: Regulation of nitrogen fixation by different nitrogen sources in the filamentous non-heterocystous cyanobacterium Microcoleus sp.
abstract: The pattern of N2 fixation, the synthesis and activity of nitrogenase under different nitrogen sources was studied in the filamentous, non-heterocystous cyanobacterium Microcoleus sp. grown under defined culture conditions. Cells grown under a 10 h light/14 h dark (10L/14D) cycle with N2 as an inorganic nitrogen source showed highest nitrogenase activity (acetylene reduction) at the end of the light phase and then a decrease after entering the dark phase. Nitrogenase synthesis was neither suppressed after 7 days of growth with 2 mM NaNO3 or 0.2 mM (NH4)2SO4 or 0.3 mM urea nor with 20 mM NaNO3 or 3 mM (NH4)2SO4 or 4 mM urea under the 10L/14D cycle. Western immunoblots tested with polyclonal antisera against the Fe-protein revealed the following: (1) the Fe-protein was synthesized in cells grown with N2 as well as in cells grown with NaNO3 or (NH4)2SO4 under the 10L/14D cycle; (2) the Fe-protein was found in cells grown with urea under the 10L/14D cycle, but not in the darkness; (3) only one protein band, corresponding to the Fe-protein, was found in cells harvested during the light phase of the 10L/14D cycle under the tested conditions. No nitrogenase activity was observed when chloramphenicol was added to the cultures 4 h before the onset of the light period. This observation suggest de novo synthesis of nitrogenase in Microcoleus sp.
authors.affiliation: Department of Biochemistry, Uppsala Biomedical Center, Sweden.
authors.forename: G E
authors.initials: GE
authors.lastname: Sroga
mesh_terms: D000114:Acetylene / Q000378:metabolism; D000458:Cyanobacteria / Q000201:enzymology*; D003624:Darkness; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000502:physiology*; D009591:Nitrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D014508:Urea / Q000378:metabolism
chemical_list: D014508:Urea; D009591:Nitrogenase; D009584:Nitrogen; D000114:Acetylene