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PubMed1989

Occurrence of multiple antibiotic resistance in Azotobacter chroococcum.

Of 117 strains of Azotobacter chroococcum, isolated from local soils the antibiotic resistance pattern to ten widely used antibiotics was determined by antibiotic disk and agar plate dilution method. Over 95% of the strains were resistant to 10 micrograms ml-1 concentration of ampicillin, chloramphenicol, erythromycin and tetracycline and 70% or more were resistant to kanamycin, nalidixic acid, rifampicin, streptomycin and trimethoprim. 1 to 8% of the strains showed resistance upto 400 micrograms ml-1 concentration of 5 antibiotics (ampicillin, chloramphenicol, kanamycin, streptomycin and tetracycline). The intrinsic resistance to the 10 antibiotics was generally high in Azotobacter chroococcum strains.

Anti-Bacterial Agents↗

PubMed1988

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.

Azotobacter↗

PubMed1985

UV-repair and mutagenesis in Azotobacter vinelandii. II. Repair and mutagenesis.

More numbers of mutants were isolated when UV-irradiated cells of Azotobacter vinelandii OP were treated with caffeine for a limited period of time after UV-irradiation. This is encouraging, considering the difficulty in isolating Azotobacter mutants. Post-irradiation treatment with acriflavine, however, yielded comparatively lesser number of mutants.

Acriflavine↗

PubMed1983

[Encystment using different carbon substrates in Azotobacter chroococcum].

Carbon nutrition has a fundamental role in the encystment of bacteria of the genus Azotobacter. The effect of liquid media with various organic carbon substrates on the encystment of 2 strains of Azotobacter chroococcum was studied. Both strains had been previously cultured in a glucose and mannitol liquid medium. Strain 2087 showed the greatest degree of encystment (78%) with isopropanol and a very low percentage of cyst formation in the glucose and mannitol medium. In strain 1847 an important percentage of cyst formation (33%) was obtained in the glucose and mannitol medium and no cysts appeared with isopropanol. N-butanol and N-propanol induced in both strains relatively reduced percentages of encystment. The differential response found in the glucose and mannitol medium and the isopropanol media with strains 2087 and 1847 of A. chroococcum, has a degree of similarity in the different intensity of encystment shown by diverse strains of A. vinelandii with certain carbon substrates.

Azotobacter↗

PubMed1982

[Azotobacter chroococcum, a producer of a new antifungal antibiotic].

Strain 92 of Azotobacter chroococcum was obtained as result of natural selection. It produces an antibiotic active against phytopathogenic fungi. The antibiotic was isolated from the bacterial mass of the culture with ethanol extraction followed by column and thin-layer chromatography on silica gel. The pure antibiotic is a viscous oily substance of a yellowish colour, readily soluble in the majority of the organic solvents, not soluble in water, readily oxidized by air oxygen. The UV absorption spectrum of the antibiotic ethanol solution had bonds characteristic of the conjugated tetraene system. The presence of ketone and enol groups in the antibiotic molecule was shown with the colour reactions. It was confirmed by the data of the antibiotic IR spectrum investigation. According to the data of high resolution mass spectroscopy the empirical formula of the antibiotic is C20H30O4, the molecular weight is 334. It is suggested that the antibiotic is an ester of aliphatic tetraenic acid differing from the known antibiotics produced by Azotobacter.

Antifungal Agents↗

PubMed1994

Utilization of some phenolic compounds by Azotobacter chroococcum and their effect on growth and nitrogenase activity.

Azotobacter chroococcum MH1 was grown in a mannitol and nitrogen free medium supplemented with p-hydroxybenzoic acid, resorcinol, catechol or vanillic acid as a sole carbon source. Growth and nitrogenase activity of p-hydroxybenzoic acid were supported by 8, 6 and 4 mM of p-hydroxybenzoic acid, resorcinol and catechol, respectively. The generation time of 1.71 h in p-hydroxybenzoic acid did not differ from a generation time of 1.64 h, when grown in mannitol. The compound p-hydroxybenzoic acid was utilized rapidly. However, the decomposition of other phenolic compounds tested proceeded slowly. These results suggested that phenolic compounds released during biodegradation of plant wastes could be utilized as carbon sources for both growth and nitrogen fixation of Azotobacter chroococcum.

Azotobacter↗

PubMed1998

Analysis of upstream activation of the vnfH promoter of Azotobacter vinelandii.

BAL-31 deletion products of the DNA fragment containing the vnfH promoter and upstream region, when cloned in a transcriptional fusion vector and analyzed for vnfH expression in Azotobacter vinelandii, revealed that the upstream activator sequence of the vnfH promoter lies about 140 nucleotides upstream of the promoter. Subsequent substitution and deletion analysis by oligonucleotide-directed mutagenesis in the upstream region of the vnfH promoter showed that sequences 5'-GTACCATGCGGAAC-3' and 5'-GTACCTGCGGGTAC-3', located 170 and 140 nucleotides upstream of the vnfH promoter, respectively, are both required for vnfH expression. Addition of four nucleotides in the intervening sequence between the vnfH promoter and the putative VnfA (analog of NifA of the conventional molybdenum-dependent nitrogen-fixation pathway) binding site resulted in a drastic reduction of expression from the vnfH promoter in Azotobacter vinelandii, whereas addition of 10 nucleotides in the intervening sequence did not affect the expression. Therefore, the face of the helix-dependent contact appeared to be important. DNA bending seemed to play a crucial role in expression from vnfH promoter. The intervening sequence exhibited characteristics of sequence-dependent intrinsically curved DNA, as shown by anomalous low gel mobility with polyacrylamide gel electrophoresis, electron microscopy, and computer simulated curvature analysis. Distamycin at very low concentrations significantly reduced the anomaly in electrophoretic mobility of the intervening DNA sequence.

Artificial Gene Fusion↗

PubMed2000

Mechanistic interpretation of the dilution effect for Azotobacter vinelandii and Clostridium pasteurianum nitrogenase catalysis.

Nitrogenase activity for Clostridium pasteurianum (Cp) at a Cp2:Cp1 ratio of 1.0 and Azotobacter vinelandii (Av) at Av2:Av1 protein ratios (R) of 1, 4 and 10 is determined as a function of increasing MoFe protein concentration from 0.01 to 5 microM. The rates of ethylene and hydrogen evolution for these ratios and concentrations were measured to determine the effect of extreme dilution on nitrogenase activity. The experimental results show three distinct types of kinetic behavior: (1) a finite intercept along the concentration axis (approximately 0.05 microM MoFe); (2) a non-linear increase in the rate of product formation with increasing protein concentration (approximately 0.2 microM MoFe) and (3) a limiting linear rate of product formation at high protein concentrations (>0.4 microM MoFe). The data are fitted using the following rate equation derived from a mechanism for which two Fe proteins interact cooperatively with a single half of the MoFe protein. (see equation) The equation predicts that the cubic dependence in MoFe protein gives rise to the non-linear rate of product formation (the dilution effect) at very low MoFe protein concentrations. The equation also predicts that the rate will vary linearly at high MoFe protein concentrations with increasing MoFe protein concentration. That these limiting predictions are in accord with the experimental results suggests that either two Fe proteins interact cooperatively with a single half of the MoFe protein, or that the rate constants in the Thorneley and Lowe model are more dependent upon the redox state of MoFe protein than previously suspected [R.N. Thornley and D. J. Lowe, Biochem. J. 224 (1984) 887-894]. Previous Klebsiella pneumoniae and Azotobacter chroococcum dilution results were reanalyzed using the above equation. Results from all of these nitrogenases are consistent and suggest that cooperativity is a fundamental kinetic aspect of nitrogenase catalysis.

Adenosine Triphosphate↗

PubMed1979

Effect of inoculation with n(2)-fixing spirilla and azotobacter on nitrogenase activity on roots of maize grown under subtropical conditions.

Inoculated and non-inoculated seedlings of maize were grown in fertile clayloam soils of Egypt and Belgium under subtropical conditions provided in a greenhouse. Acetylene-reducing activity and microbial counts were determined during a period ranging from 6 to 12 weeks after sowing. Irrespective of soil origin, N(2)-fixing spirilla and Azotobacter were common under maize cultivation. Inoculation resulted in a transitional increase in their numbers at early stages of growth. Nitrogenase activity was not detected in the rhizosphere of young plants. The maximum activities measured (81 to 1,436 nmol of C(2)H(4) g h) occurred close to the 50 to 70% silking stage. Inoculation with N(2)-fixing spirilla, particularly in Nile Delta soil, doubled the amount of N(2) fixed in a late period of growth (12 weeks), whereas inoculation with Azotobacter had no noticeable effect.

Journal Article↗

PubMed1986

Stimulation of Agrobacterium tumefaciens Growth by Azotobacter vinelandii Ferrisiderophores.

Azotobacter vinelandii stimulated the growth of Agrobacterium tumefaciens H2, H23, H24, H27, and ATCC 15955 on media containing insoluble iron sources. The Azotobacter vinelandii siderophores appeared to promote Agrobacterium tumefaciens growth by solubilizing mineral iron, and the ferrisiderophores so formed then acted as iron sources for Agrobacterium tumefaciens. Agrobactin, the Agrobacterium siderophore, appeared to be inefficient in solubilizing mineral iron directly.

Journal Article↗

PubMed1994

The DeLey-Doudoroff Pathway of Galactose Metabolism in Azotobacter vinelandii.

Azotobacter vinelandii cell extracts reduced NAD and oxidized d-galactose to galactonate that subsequently was converted to 2-keto-3-deoxy-galactonate. Further metabolism of 2-keto-3-deoxy-galactonate required the presence of ATP and resulted in the formation of pyruvate and glyceraldehyde 3-P. Radiorespirometry indicated a preferential release of CO(2) at the first carbon position of the d-galactose molecule. This suggested that Azotobacter vinelandii metabolizes d-galactose via the DeLey-Doudoroff pathway. The first enzyme of this pathway, d-galactose dehydrogenase, was partially characterized. It has a molecular weight of about 74,000 Da and an isoelectric point of 6.15. The pH optimum of the galactose dehydrogenase was about 9. The apparent K(m)s for NAD and d-galactose were 0.125 and 0.56 mM, respectively. Besides d-galactose, the active fraction of this galactose dehydrogenase also oxidized l-arabinose effectively. The electron acceptor for d-galactose or l-arabinose oxidation, NAD, could not be replaced by NADP. These substrate specificities were different from those reported in Pseudomonas saccharophila, Pseudomonas fluorescens, and Rhizobium meliloti.

Journal Article↗

PubMed1995

Alternative Function of the Electron Transport System in Azotobacter vinelandii: Removal of Excess Reductant by the Cytochrome d Pathway.

The N(inf2)-fixing bacterium Azotobacter vinelandii was grown in an O(inf2)-regulated chemostat with glucose or galactose as substrate. Increasing the O(inf2) partial pressure resulted in identical synthesis of the noncoupled cytochrome d terminal oxidase, which is consistent with the hypothesis that A. vinelandii uses high rates of respiration to protect the nitrogenase from oxygen. However, cell growth on glucose showed a lower yield of biomass, higher glycolytic rate, higher respiratory rate, and lower cytochrome o content than cell growth on galactose. Elemental analysis indicated no appreciable change in the C-to-N ratio of cell cultures, suggesting that the major composition of the cell was not influenced by the carbon source. A poor coordination of glucose and nitrogen metabolisms in A. vinelandii was suggested. The rapid hydrolysis of glucose resulted in carbonaceous accumulation in cells. Thus, Azotobacter species must induce a futile electron transport to protect cells from the high rates of glucose uptake and glycolysis.

Journal Article↗

PubMed1961

EFFECT OF TUNGSTATE ON THE UPTAKE AND FUNCTION OF MOLYBDATE IN AZOTOBACTER AGILIS.

Bulen, William A. (Charles F. Kettering Foundation, Yellow Springs, Ohio). Effect of tungstate on the uptake and function of molybdate in Azotobacter agilis. J. Bacteriol. 82:130-134. 1961.-The reported competitive inhibition of molybdate by tungstate was investigated in an effort to elucidate molybdenum functions associated with nitrogen fixation by Azotobacter agilis (A. vinelandii). Growth, respiration, and N(2) (15)-incorporation experiments with normal and molybdenum-deficient cells indicated that tungstate inhibits the uptake of molybdate but does not compete with the metabolically functional molybdenum of cells metabolizing N(2). Neither a molybdenum requirement nor a tungstate inhibition was observed with cells metabolizing urea.

Journal Article↗

PubMed1962

LOCALIZATION OF RESPIRATORY ENZYMES IN INTRACYTOPLASMIC MEMBRANES OF AZOTOBACTER AGILIS.

Pangborn, J. (University of California, Davis), Allen G. Marr, and S. A. Robrish. Localization of respiratory enzymes in intracytoplasmic membranes of Azotobacter agilis. J. Bacteriol. 84:669-678. 1962.-Thin sections of the cells of Azotobacter agilis which have been disrupted by sonic treatment, by osmotic shock, or by ballistic disintegration reveal a network of internal membranes in the form of vesicles and tubules. The internal membranes are attached to the envelope. Treatment in a Mickle disintegrator of envelopes emptied of cytoplasm by osmotic shock results in the loss of the internal membranes and a concomitant release of reduced diphosphopyridine nucleotide oxidase from the envelopes. Thus, the intracytoplasmic membranes are the probable locus of the respiratory enzymes of the cell. Thin sections of whole cells show tubular intracytoplasmic membranes which are obscured by ribosomes and other dense cytoplasmic constituents.

Journal Article↗

PubMed1961

Development and germination of the Azotobacter cyst.

The fine structure of Azotobacter vinelandii has been studied by means of electron microscopy of ultrathin sections made of the encysting and germinating cells. The organisms were fixed with KMnO(4) and embedded in epoxy resin. On an encystment medium the rod-shaped bacteria begin to assume an almost spherical form and then bark-like exine appears in 1(1/2) to 2 days. The exine thickens and an electron permeable intine forms between it and the shrinking cell body. In 5 days the intine makes up more than half of the cyst volume and begins to show a definite two-layered structure. Meanwhile the peripheral bodies, which may be extensions of the cell membrane of the vegetative cell, disappear as the encystment progresses. The cell wall and membrane of the vegetative cell remain demonstrable as the confining structure of the shrinking central body of the mature cyst. In this central body lipoidal globules appear together with aggregations of nuclear material. Cyst germination begins with an increase in the size of the central body at the expense of the intine. The nuclear aggregations become more diffuse and the lipoidal globules disappear. The exine may be pushed outward and the bark-like fragments separate as the emerging vegetative cell develops. Invagination of the cell wall and membrane may occur at this stage leading to cell division. Empty exines remain as horseshoe-shaped structures.

Azotobacter↗

PubMed2026

Azotobacter vinelandii gene fitness following carbon shift from sucrose to acetate, succinate and glycerol.

Nitrogen-fixing microbes are a primary contributor of this important nutrient to the global nitrogen cycle. Biological nitrogen fixation (BNF) through the enzyme nitrogenase requires extensive energy that in whole cells is generally studied during the oxidation of carbohydrates such as sugars. The nitrogen-fixing bacterium Azotobacter vinelandii is a model diazotroph for the study of aerobic BNF. Much is known about metabolism in A. vinelandii when cultured on a simple medium where energy is provided primarily in the form of sucrose or glucose. Outside of the laboratory, this soil bacterium grows on metabolites primarily derived from plant root exudates or from the degradation of dead plant matter. In this work, we expand on previous studies looking at genes that are essential to BNF in A. vinelandii when grown on sucrose medium using transposon sequencing (Tn-seq). We applied Tn-seq to determine the genes essential to growth when the medium was shifted to acetate, succinate or glycerol as the primary carbon and energy source to fuel both growth and BNF. A global overview of the genes of central metabolism and those directing substrates toward central metabolism, along with a selection of unexpected genes that were essential for specific growth substrates, is provided.

Azotobacter vinelandii↗

PubMed1998

FtsZ from Escherichia coli, Azotobacter vinelandii, and Thermotoga maritima--quantitation, GTP hydrolysis, and assembly.

We have cloned the ftsZ genes from Thermotoga maritima and Azotobacter vinelandii and expressed the proteins (TmFtsZ and AzFtsZ) in Escherichia coli. We compared these proteins to E. coli FtsZ (EcFtsZ), and found that several remarkable features of their GTPase activities were similar for all three species, implying that these characteristics may be universal among FtsZs. Using a calibrated protein assay, we found that all three FtsZs bound 1 mole guanine nucleotide per mole FtsZ and hydrolyzed GTP at high rates (> 2 GTP per FtsZ per min). All three required magnesium and a monovalent cation for GTP hydrolysis. Previous reports showed that EcFtsZ (and some other species) required potassium. We confirmed this specificity for EcFtsZ but found that potassium and sodium both worked for Az- and TmFtsZ. Specific GTPase activity had a striking dependence on FtsZ concentration: activity (per FtsZ molecule) was absent or low below 50 microg/ml, rose steeply from 50 to 300 microg/ml and plateaued at a constant high value above 300 microg/ml. This finding suggests that the active state requires a polymer that is assembled cooperatively at 50-300 microg/ml. A good candidate for the active polymer was visualized by negative stain electron microscopy--straight protofilaments and protofilament pairs were seen under all conditions with active GTPase. We suggest that the GTP hydrolysis of FtsZ may be coupled to assembly, as it is for tubulin, with hydrolysis occurring shortly after an FtsZ monomer associates onto a protofilament end. As a part of this study, we determined the concentration of EcFtsZ and TmFtsZ by quantitative amino acid analysis and used this to standardize the bicinchonic acid colorimetric assay. This is the first accurate determination of FtsZ concentration. Using this standard and quantitative Western blotting, we determined that the average E. coli cell has 15,000 molecules of FtsZ, at a concentration of 400 microg/ml. This is just above the plateau for full GTPase activity in vitro.

Actin Cytoskeleton↗

PubMed1979

Nitrogenase activity of immobilized Azotobacter vinelandii.

As part of a program to investigate the use of biological nitrogen fixation for fertilizer ammonia production, an investigation into the immobilization of the aerobic, nitrogen-fixing bacterium, Azotobacter vinelandii was undertaken. Immobilization was acaccomplished by adsorption onto an anionic exchange cellulose (Cellex E) with loadings as high as 10'' cells/g resin. Immobilized cell preparations were tested under both batch and continuous-flow conditions. Nitrogenase activities as high as 4200 nmol/min g resin were observed as measured by the acetylene reduction assay. Immobilized cells retained their activity for as long as 117 hr in a continuous-flow reactor. Activity loss appeared to be related to the development of a variant strain.

Acetylene↗