Growth of Spirillum Lipoferum At Constant Partial Pressures of Oxygen, and the Properties of its Nitrogenase in Cell-free Extracts

Abstract

SUMMARY: 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. lipofernum 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 °, and activity was restored by adding purified Feprotein from other N2-fixing bacteria.