Reduction of Nitrates by Azotobacter indicum and Azotobacter chroococcum Cultures

The capacity for denitrification was studied in Azotobacter bacteria, which are free-living nitrogen-fixing obligatory aerobes. Data on nitrate reduction to nitrites and nitric oxide by A. indicum under anaerobic conditions were obtained for the first time for genus Azotobacter.     

Reduction of nitrates by cultures of Azotobacter indicum and Azotobacter chroococcum

The capacity for denitrification was studied in Azotobacter bacteria, which are free-living nitrogen-fixing obligatory aerobes. Data on the nitrate reduction to nitrites and nitric oxide by A. indicum under anaerobic conditions were obtained for the first time for genus Azotobacter.     

Phospholipids of Azotobacter vinelandii

Analyses of resting cells of Azotobacter vinelandii revealed that numerous phospholipids were present that did not concentrate in the membranous R(3) fraction which carried out electron transport function.     

Ultrastructure of Azotobacter vinelandii

Vegetative cells and cysts of Azotobacter vinelandii 12837 were prepared for electron microscopy by several methods assumed to preserve structural details destroyed by techniques previously reported in the literature. Examination of large numbers of cells and cysts by these methods revealed four structural details not reported previously: intine fibrils, intine vesicles, intine membrane, and microtubules. The intine fibrils form a network in the gel-like homogeneous matrix of the CC2 layer. Intine vesicles which seem to originate in the cell wall complex of the central body are seen in the intine and exine of cysts. Analogous structures are found on vegetative cells. The intine is divided into two chemically distinct areas by the two-layered intine membrane. Microtubules, previously reported only in vegetative cells, were found in cysts.     

Calcium requirements of Azotobacter

Summary Calcium was essential for the growth of A. vinelandii, A. chroococcum, A. beijerinckii and A. insigne in the presence and absence of combined nitrogen. A. agile and A. macrocytogenes were able to grow in the absence of calcium but growth was stimulated by the cation.Calcium could be replaced by strontium at roughly the same molar concentration.The authors present evidence suggesting that the calcium sparing effect of ammonium and sodium acetates reported in the literature may be dependent on the size of inoculum used.Professor Dr. Dr. h. c. A. Rippel zum 70. Geburtstag.     

The vanadium-containing nitrogenase of Azotobacter

Fifty years after a role of vanadium in biological fixation was proposed, it was shown that in addition to their well-characterized molybdendum nitrogenases, Azotobacter chroococcum and Azotobacter vinelandii both have a genetically distinct nitrogenase system in which the conventional molybdoprotein is replaced by a vanadoprotein. Both Mo-nitrogenases and V-nitrogenases have similar requirements for activity: MgATP, a low potential reductant and the absence of oxygen. The genes encoding the V-nitrogenase are expressed only under conditions of Mo-deficiency. V-Nitrogenase of A.chroococcum is made up of a tetrameric VFe protein (Mr 210,000) with an alpha 2 beta 2 structure containing two V atoms, 23 Fe atoms and 20 acid-labile sulphide atoms per tetramer, and a dimeric Fe protein (Mr 64,000) with a gamma 2 structure containing four Fe atoms and four acid-labile sulphide atoms per dimer. Vanadium K-edge X-ray absorption spectroscopy indicates that V in the VFe protein, like Mo in MoFe protein, has S, Fe and possibly O as nearest neighbours. A vanadium- and iron-containing cofactor (FeVaco) can be extracted from the VFe protein and will restore C2H2 reductase, but no nitrogenase activity, to the inactive MoFe protein accumulated by mutants unable to synthesize the molybdenum- and iron-containing co-factor of Mo-nitrogenase. The products of C2H2 reduction by the hybrid protein (C2H6 as well as C2H4) are a characteristic of the VFe protein and provide evidence that FeVaco is, or forms part of the active site of V-nitrogenase.     

Sodium-Dependent Growth of Azotobacter chroococcum

Selected ion-monitoring gas chromatography-mass spectrometry was used for detection of beta-hydroxy fatty acids as an independent assay for the presence or absence of endotoxin in materials claimed to induce nonspecific activation of Limulus amoebocyte lysate. To this end, suspensions of gram-negative and -positive bacteria, one fungal species, cerebrospinal fluid, and hollow-fiber hemodialyzer rinses were assayed for endotoxin by gas chromatography-mass spectrometry and the Limulus amoebocyte lysate assay. Good qualitative agreement was shown for both methods when suspensions of test organisms were assayed. Two false-negative results were obtained by gas chromatography-mass spectrometry assays of cerebrospinal fluid and were shown to be a result of insufficient endotoxin in the cerebrospinal fluid specimens for detection by gas chromatography-mass spectrometry. Hemodialyzer rinses were Limulus assay positive; however, no beta-hydroxy fatty acids were detected by gas chromatography-mass spectrometry. These data were compared with data obtained from USP rabbit pyrogen tests of the rinse materials (nonpyrogenic) and chemical characterization of the Limulus assay-reactive rinses, which showed the rinses to be cellulosic in nature. It is suggested that beta-hydroxy fatty acids, as assayed by selected ion-monitoring gas chromatography-mass spectrometry, be used as chemical marker molecules for the presence or absence of endotoxin in materials reported to cause nonspecific activation of Limulus amoebocyte lysate.     

Plasmids of Azotobacter vinelandii.

Four laboratory strains and two isolates of Azotobacter vinelandii were found to contain plasmids. Twenty-five laboratory strains which could fix nitrogen did not have free, covalently closed circular plasmid DNA. The plasmids varied in size from 9 to 52 megadaltons, and each strain yielded only one plasmid. No discernible differences in ability to fix nitrogen were found between plasmid-bearing and cured cultures.