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At least 19 recordsLinked to original sources
PubMed1988

Identification and characterization of two nitrogen fixation regulatory regions, nifA and nfrX, in Azotobacter vinelandii and Azotobacter chroococcum.

Five Tn5-induced Nif- mutants of Azotobacter vinelandii were characterized as regulatory mutants because they were restored to Nif+ by the introduction of constitutively expressed nifA from Klebsiella pneumoniae. The mutants fell into two different classes on the basis of hybridization to a Rhizobium leguminosarum nifA gene probe and by complementation with cosmids isolated from pLAFRI gene banks of A. vinelandii and Azotobacter chroococcum. One mutant, MV3, was located in or near a nifA gene. The others, MV12, MV16, MV18 and MV26, defined a new regulatory gene, which has been called nfrX. The lack of expression of different nif-lacZ fusions confirmed the regulatory phenotype of all five mutant strains. The ability of both nifA and nfrX mutants to grow on nitrogen-free medium with vanadium, but not on medium with molybdenum, suggests that neither gene is required for expression of the alternative V-containing nitrogenase of A. vinelandii. A fragment carrying Tn5 and flanking DNA from MV3 was used as a probe to isolate the nifA region of A. chroococcum. Ligation of two adjacent EcoRI fragments of A. chroococcum yielded an intact nifA gene that activated expression of nifH-lac fusions and also restored MV3 to Nif+. The four nfrX mutants were complemented by pLAFR1 cosmids pLV163 and pLC121. The nfrX gene was subcloned from pLV163 and located within a 3.2 kb fragment. To determine whether nfrX might be found in other nitrogen-fixing organisms, DNA from 13 different species was hybridized to an nfrX probe. The failure to observe hybridization suggests that nfrX may be specific to nif regulation in Azotobacter.

Azotobacter↗
PubMed2005

Production of amino acids by Azotobacter vinelandii and Azotobacter chroococcum with phenolic compounds as sole carbon source under diazotrophic and adiazotrophic conditions.

Azotobacter vinelandii strain ATCC 12837 and Azotobacter chroococcum strain H23 (CECT4435) were tested to grow in N-free or NH(4)Cl amended chemically defined media, with protocatechuic acid or sodium p-hydroxybenzoate as sole carbon (C) sources at a concentration of 2 mmol/L. Both substrates supported grow at similar rates than bacteria grown in control media amended with 2 mmol/L sodium succinate as C source. The two strains produced aspartic acid, serine, glutamic acid, glycine, hystidine, threonine, arginine, alanine, proline, cysteine, tyrosine, valine, methionine, lysine, isoleucine, leucine and phenylalanine after 72 h of growth in chemically defined media with 2 mmol/L of phenolic compounds or sodium succinate as sole C source amended or unamended with 0.1% (w/v) NH(4)Cl. Qualitative and quantitative production of all amino acids was not affected by the use of different C and N substrates.

Amino Acids↗
PubMed1986

Electron transfer to nitrogenase. Characterization of flavodoxin from Azotobacter chroococcum and comparison of its redox potentials with those of flavodoxins from Azotobacter vinelandii and Klebsiella pneumoniae (nifF-gene product).

Flavodoxin in the hydroquinone state acts as an electron donor to nitrogenase in several nitrogen-fixing organisms. The mid-point potentials for the oxidized-semiquinone and semiquinone-hydroquinone couples of flavodoxins isolated from facultative anaerobe Klebsiella pneumoniae (nifF-gene product, KpFld) and the obligate aerobe Azotobacter chroococcum (AcFld) were determined as a function of pH. The mid-point potentials of the semiquinone-hydroquinone couples of KpFld and AcFld are essentially independent of pH over the range pH 7-9, being -422 mV and -522 mV (normal hydrogen electrode) at pH 7.5 respectively. The mid-point potentials of the quinone-semiquinone couples at pH 7.5 are -200 mV (KpFld) and -133 mV (AcFld) with delta Em/pH of -65 +/- 4 mV (KpFld) and -55 +/- 2 mV (AcFld) over the range pH 7.0-9.5. This indicates that reduction of the quinone is coupled to protonation to yield a neutral semiquinone. The significance of these values with respect to electron transport to nitrogenase is discussed. The amino acid compositions, the N- and C-terminal amino acid sequences and the u.v.-visible spectra of KpFld and AcFld were determined and are compared with published data for flavodoxins isolated from Azotobacter vinelandii.

Amino Acid Sequence↗
PubMed2000

Isolation and characterization of nifDK::kanamycin and nitrogen fixation proficient Azotobacter vinelandii strain, and its implication on the status of multiple chromosomes in Azotobacter.

Several lines of experimental analyses on the ploidy status of Azotobacter vinelandii genome lead to the conclusion that it contains more than 40 copies of its chromosome and therefore it is a polyploid organism. The genetic evidence argues against the existence of polyploidy in these cells since the segregation pattern of genetic markers under lack of selection pressure mimic that of haploids. However, when A. vinelandii was made Nif- by inserting a kanamycin resistance marker gene in the nifDK sequence and the cells were selected for kanamycin resistance and Nif+ phenotype, we were able to score colonies that are both kanamycin resistant and Nif+. Therefore, when the cells were subjected to forced double selection of the same locus, they behaved as if they carried at least two chromosomes, one carrying the kanamycin resistance marker in the nifDK genes and the other carrying the intact nifDK genes. These analyses suggested that at least a diploidy status can be induced in these cells under selection pressure.

Azotobacter vinelandii↗
PubMed1981

Proton magnetic resonance studies of Azotobacter vinelandii ferredoxin I. Evidence for a difference in coordination of the 3Fe centers in azotobacter vinelandii ferredoxin I and desulfovibrio gigas ferredoxin II.

Proton magnetic resonance studies have been made of Azotobacter vinelandii ferredoxin I. This protein contains a low potential 3Fe-3S center (Emp = -424 mV) and a high potential 4Fe-4S center (Emp = +320 mV). A series of five single proton resonances are visible downfield of 11 ppm in the isolated form of the protein. On reduction of the protein the three most downfield resonances are no longer visible and no new resonances are observed. These resonances are assigned to alpha-CH cysteinyl protons on residues 8, 20, and 49 which coordinate the 3Fe center. The two remaining downfield resonances are altered on oxidation of the protein, and are assigned to beta-CH2 cysteinyl protons on residues bound to the high potential 4Fe center. Comparison of the reported NMR spectrum of Desulfovibrio gigas ferredoxin II (Moura, J. J. G., Xavier, A. V., Bruschi, M., and Le Gall, J. (1977) Biochim. Biophys. Acta 459, 278-289) to that of A. vinelandii ferredoxin I is made. The 3Fe centers found in D. gigas ferredoxin Ii exhibit a reduction potential almost 300 mV more positive than the 3Fe center in A. vinelandii ferredoxin I. Evidence is presented that the 3Fe centers in the two proteins are not co-ordinated identically, and arguments are made which suggest that a small noncysteinyl ligand, modeled as a nonprotein oxygen atom in the x-ray structure A. vinelandii ferredoxin I, may be replaced in D. gigas ferredoxin II by a glutamyl epsilon-oxygen linkage to an iron atom. Further, it is noted that such a change could be responsible for the significant difference in reduction potential observed between the 3Fe centers in these two proteins.

Azotobacter↗