产酸丙酸杆菌耐酸菌株的选育及其应用

为了解除微生物发酵生产丙酸过程中代谢产物(丙酸)对菌体生长的抑制作用,以实验室保藏的产酸丙酸杆菌(耐30g/L丙酸)为出发菌株P-0,通过丙酸压力筛选获得了一株耐10g/L丙酸的产酸性能良好的菌株P-10,降低了发酵过程中丙酸对菌体生长的抑制作用。菌株P-10做摇瓶发酵,发酵周期168h,丙酸浓度为49.66g/L,产酸速率为0.30g/(L·h),较出发菌株P-0提高了53.04%;7L发酵罐实验表明,菌株P-10发酵周期168h,丙酸浓度为55.63g/L,产酸速率0.33g/(L·h)。同时对菌株P-10做二次接种实验,结果表明,84h为二次接种最适时间段,且84h进行二次接种时,丙酸浓度提高了17.77%,二次接种实验不但有利于有机酸的积累,而且可以提高菌株的产酸能力和耐酸能力;经过选育的菌株P-10具有优良的产酸稳定性,有利于菌种的工业化生产和应用,同时对后续的发酵分离耦合具有重要意义。     

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.     

产酸丙酸杆菌耐酸菌株的选育及其应用

为了解除微生物发酵生产丙酸过程中代谢产物(丙酸)对菌体生长的抑制作用,以实验室保藏的产酸丙酸杆菌(耐30g/L丙酸)为出发菌株P-0,通过丙酸压力筛选获得了一株耐10g/L丙酸的产酸性能良好的菌株P-10,降低了发酵过程中丙酸对菌体生长的抑制作用。菌株P-10做摇瓶发酵,发酵周期168h,丙酸浓度为49.66g/L,产酸速率为0.30g/(L·h),较出发菌株P-0提高了53.04%;7L发酵罐实验表明,菌株P-10发酵周期168h,丙酸浓度为55.63g/L,产酸速率0.33g/(L·h)。同时对菌株P-10做二次接种实验,结果表明,84h为二次接种最适时间段,且84h进行二次接种时,丙酸浓度提高了17.77%,二次接种实验不但有利于有机酸的积累,而且可以提高菌株的产酸能力和耐酸能力;经过选育的菌株P-10具有优良的产酸稳定性,有利于菌种的工业化生产和应用,同时对后续的发酵分离耦合具有重要意义。     

Acid-resistant bovine pestivirus requires activation for pH-triggered fusion during entry

The route of internalization of the pestivirus bovine viral diarrhea virus (BVDV) was studied by using different chemical and biophysical inhibitors of endocytosis. Expression of the dominant-negative mutant Dyn(K44A) of the GTPase dynamin in MDBK cells, as well as the treatment of the cells with chlorpromazine and beta-methyl-cyclodextrin inhibited BVDV entry. BVDV infection was also abolished by potassium (K+) depletion, hyperosmolarity, and different inhibitors of endosomal acidification. We conclude that BVDV likely enters the cell by clathrin-dependent endocytosis and that acidification initiates fusion with the endosomal membrane. Further studies revealed that BVDV was unable to undergo "fusion from without" at low pH. The finding that low pH is not sufficient to force adsorbed BVDV into fusion with the plasma membrane is compatible with the remarkable resistance of pestiviruses to inactivation by low pH. The importance of the abundant intra- and intermolecular disulfide bonds in BVDV glycoproteins for virus stability was studied by the use of reducing agents. The combination of dithiothreitol and acidic pH led to partial inactivation of BVDV and allowed fusion from without at low efficiency. Evidence is provided here that acid-resistant BVDV is destabilized during endocytosis to become fusogenic at an endosomal acidic pH. We suggest that destabilization of the virion occurs by breakage of disulfide bonds in the glycoproteins by an unknown mechanism.     

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.