Growth of Spirillum lipoferum at constant partial pressures of oxygen, and the properties of its nitrogenase in cell-free extracts.
Spirillum lipoferum, an N2-fixing organism, was grown at constant concentrations of dissolved O2. When supplied with NH4+ aerobically, its doubling time was 1 h; when it fixed N2 microaerophilically, its doubling time was 5-5 to 7 h and the optimal PO2 for growth was 0-005 to 0-007 atm. At its optimal PO2 for growth on N2, S. lipoferum assimilated 8 to 10 mg nitrogen/g carbon substrate used; its efficiency was less at higher PO2 levels. Nitrogenase in cell-free extracts required Mg2+ and Mn2+, and the Fe-protein was activated by Rhodospirillum rubrum activating factor. The nitrogenase had an optimal pH of 7-1 to 7-4 and an apparent Km for acetylene of 0-0036 atm. Extracts of S. lipoferum lost their nitrogenase activity on storage at -18 degrees C, and activity was restored by adding purified Fe-protein from other N2-fixing bacteria.
D000114:Acetylene / Q000378:metabolism; D000643:Ammonium Chloride / Q000378:metabolism; D001426:Bacterial Proteins / Q000494:pharmacology; D002474:Cell-Free System; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen; D010313:Partial Pressure; D013139:Spirillum / Q000201:enzymology / Q000254:growth & development*; D013696:Temperature
D001426:Bacterial Proteins; D000643:Ammonium Chloride; D009591:Nitrogenase; D000114:Acetylene; D010100:Oxygen