Cultures Of Azospirillum Research Articles

Response of on farm produced organic inputs on soil, plant nutrient status, yield and quality of guava (Psidium guajava) cv Allahabad Safeda

A field experiment was conducted during 2008-09 to compare the efficacy of different organic inputs in the production of guava (Psidium guajava L.) cv Allahabad Safeda. The highest number of fruits (363/tree) and yield (41.45 kg/tree) was recorded by application of 250 g rhizospheric soil of Ficus bengalensis + 5% Amritpani + organic mulching followed by 328 fruits/tree and yield of 31.76 kg/tree by biodynamic compost (30 kg/tree). Maximum TSS (11.7 °Brix) in fruits was recorded through application of biodynamic compost fortified with BD-500 (30 kg/tree) and cow pat pit (100 g/tree) followed by 11.3 °Brix with of vermicompost (30 kg/tree) + Azospirillum culture (250 g/ tree) + PSB (50 g/tree). The treatments did not affect acidity, ascorbic acid and reducing sugars significantly. Microbial analysis of different organic inputs indicated that cow pat pit contained maximum load of Azotobacter sp (1.5 × 106 cfu/g) and Azospirillum sp (1.3 × 106 cfu/g). Rhizospheric soils of Ficus bengalensis contained maximum number (1.5 × 105 cfu/g) of Azotobacter and (1.4 × 107 cfu/g) Azospirillum as compared to mango (2 × 104 cfu/g and 1.2 × 104 cfu/g, respectively). After two years of experimentation, maximum organic carbon (0.818%) was recorded in the basin soil of treatment biodynamic compost fortified with BD-500 (30 kg/tree) and cow pat pit (100 g/tree). On the other hand, highest build of available P (67.6 ppm) was maximum with application of biodynamic compost @ 30 kg/ tree, while available K (384 ppm), Zn (14.12 ppm), Cu (11.20 ppm) and Fe (15.7 ppm) were maximum with application of biodynamic compost fortified with BD-500 (30 kg/tree) and cow pat pit (100 g/tree), compared to initial soil nutrient status. Improvement in leaf nutrient status was also noticed and maximum leaf N (1.68%), P (0.244%), K (1.74%), Ca (1.49%), Zn (33.8 ppm) with application of rhizospheric soil of Ficus bengalensis @ 250 g/tree + 5% Amritpani + organic mulching, Mg (0.63%); with vermicompost (30 kg/tree) + Azospirillum culture (250 g/tree) + PSB (50 g/tree), Cu (78.7 ppm) and Mn (195.1 ppm) were recorded with FYM (30 kg/tree as compared to control (1.21%, 0.212%, 1.23%, 1.33%, 0.21 ppm, 27.5 ppm, 46.4 ppm and 167.6 ppm, respectively).

Optimization of biofloc production in Azospirillum brasilense (MTCC-125) and evaluation of its adherence with the roots of certain crops

The phenomenon of flocculation in Azospirillum brasilense (MTCC-125) was studied under different combinations of carbon and nitrogen sources. Fructose and Potassium nitrate at a pH of 6.4 in the cultural medium favour a higher bio-floc production. The biofloc was studied for root adhesion and its survival efficiency in the rhizoplane and rhizosphere of certain crops such as sorghum and sunflower under dryland condition. It has been demonstrated that the flocculated cultures of Azospirillum were found to have maximum adhesion to the root surface and higher survival rate in the rhizoplane and rhizosphere under different moisture stressed conditions as compared to the log phase cells of Azospirillum.

Effect of Azotobacter and Azospirillum inoculation under graded levels of nitrogen on growth and yield of sugarcane (Saccharum oflcinarum)

A field experiment conducted during 1990-91 to 1992-93 with sugarcane (Sacchnrum officinarum L.) indicated that application.of graded levels of nitrogen along with inoculation of 2cultures increased the cane and sugar yields to the extent of 7.30 and 0.78 m tonsha respectively compared with the uninoculated control. The gemination. tillering, number of millable canes, girth and cane height were also improved due to Azotobacter and Azospirillum culture combination. Maximum response was observed in Azotobncter + Azospirillum culture with nitrogen. There was a saving of fertilizer N to the extent of 25-50 kgha and im- provement in soil properties.

Response of direct seeded and transplanted pearlmillet (Pennisetum glaucum) to nitrogen, phosphorus and biofertilizers in intercropping system

A field experiment was conducted during the rainy (kharif) seasons of 1999 and 2000, at New Delhi, to study nutrient management in pearlmillet [Pennisetum glaucum (L.) R. Br. emend. Stuntz.]. Hybrid Pusa 23 in sole and intercropping system with cowpea [Vigna unguiculata (L.) Walp.] Variety Pusa Komal under direct seeded and transplanted conditions. The crops were grown with varying levels of 1, P,O, along with biofertilizers (Azospirillum culture VAM). The treatments comprised 4 main plot treatments with 2 methods of planting pearlmillet with and without intercrop and 7 levels of fertilizers. The transplanting of pearlmillet was on a par with direct seeding. Al though the transplanted crop had lower grain weightlear and shorter ear length, it had more ears/m2 and greater 1,000 grain weight than direct seeded crop which led to similar yield under both the conditions. The grain yield of pearlmillet with application of 40 kg N 30 kg P20 ha along with biofertilizers was at par with recommended dose of 60 kg N 45 kg P205/ha indicating saving of 20 kg N and 15 kg P,OJha through biofertilizers. There was no ef fect of cowpea intercropped with pearlmillet in both the years.

The Role of Wheat Germ Agglutinin in Plant–Bacteria Interactions: A Hypothesis and the Evidence in Its Support

Wheat plants are known to develop the associative symbiosis with the rhizobacterium Azospirillum brasilense.We studied the interaction of a lectin, wheat germ agglutinin (WGA), which is also found in wheat roots, with A. brasilense, strain sp245. When added to the azospirillum culture to the final concentration of 10–8to 10–9M, WGA enhanced IAA production, dinitrogen fixation, and ammonium excretion by bacterial cells. WGA also promoted the synthesis of proteins, both new and those already present in bacterial cells. The hypothesis that WGA is a signal molecule rerouting the bacterial metabolism in the direction favorable for the growth and development of the host plant has been put forward. It is suggested that signal properties of WGA are the basis for one of the functions of this lectin and essential for the effective associative symbiosis.

Pectin decomposition by mixed cultures of Azospirillum spp. and Penicillium corylophillum and its role in Azospirillum-host plant association

Mixed cultures of Azospirillum brasilense SP7 and Penicillium corylophillum allowed the efficient utilization of pectin as a carbon source for nitrogen fixation by the former organism. 93% of pectin was degraded in mixed cultures after 9-days of incubation. PG activity in separate cultures, was about 20-fold higher in P. corylophillum than that of A. brasilense. Oxalic acid was produced during pectin degradation, and the possible role of oxalate in enhancing PG activity and affecting nitrogen fixation by A. brasilense was discussed. NaCl stimulated PG production by A. lipoferum st. 137 and the maximum production was obtained at 0.05 M after 4 days of incubation. In a micro vegetative experiment with Zea mays inoculated with A. lipoferum st. 137 in presence of different concentrations of NaCl, inoculated roots exhibited higher PG production as compared with the control treatments at 0.05 M NaCl. Increase in PG production was accompanied by increase in total Azospirillum counts in the histoshpere, dry matter and plant total N-yield. It was suggested that PG production by A. lipoferum in vivo could be used as an indicator for successful Azospirillum-host plant association.

Hydrolysis of [17,17-2H2]gibberellin A20-glucoside and [17,17-2H2]gibberellin A20-glucosyl ester by Azospirillum lipoferum cultured in a nitrogen-free biotin-Based chemically-defined medium

Azospirillum lipoferum strain USA 5b, a gibberellin producing bacterium, was cultured in a nitrogen-free biotin-based chemically-defined medium in the presence of the glucosyl ester or the 13-O-glucoside of [17,17-2H2]-gibberellin A20. The [17,17-2H2]-gibberellin A20 conjugates were added at both the stationary phase of the cultures and at the beginning of the growth curve. Metabolism of the conjugates was examined after 72 h of incubation using capillary gas chromatography-mass spectrometry, with identification by full scan mass spectra. Metabolites identified were [17,17-2H2]-gibberellin A20, [17,17-2H2]-gibberellin A1 and [17,17-2H2]-gibberellin A3. Also, in the Azospirillum cultures fed at the beginning of the growth curve, gibberellin A5 and gibberellin A20 were characterized as endogenous by mass spectrometry/full spectrum. These results support the concept that the growth promotion in plants that is induced by Azospirillum infection may occur by a combination of both gibberellin production and gibberellin-glucoside/glucosyl ester deconjugation by the bacterium.

Ammonification and nitrification in soils, and nitrogen fixation by Azospirillum sp. as influenced by cypermethrin and fenvalerate

Mineralization of peptone-nitrogen and oxidation of ammoniacal nitrogen were significantly enhanced in two agricultural soils when treated with up to 5 kg ha −1 of cypermethrin or fenvalerate. The rate of ammonification and nitrification after 2 and 4 weeks was fairly rapid in the soils receiving 2.5 kg ha −1 of either insecticide. The enhancement of both transformations, mediated by microorganisms, was more pronounced in the fenvalerate-treated soils. Cultures of Azospirillum sp., isolated from insecticide-treated soils, exhibited greater nitrogen-fixing activity that lasted for at least three generations.

Pectin decomposition and associated nitrogen fixation by mixed cultures of Azospirillum and Bacillus species.

Cocultures of different Azospirillum species with Bacillus polymyxa or Bacillus subtilis allow the efficient utilization of pectin as carbon and energy sources for nitrogen fixation. The nitrogenase activity obtained with cocultures was as high as 30-80 nmol C2H4 h-1 mL-1, a much higher value than that obtained with pure cultures of either Azospirillum (up to 13 nmol C2H4 h-1 mL-1) or B. polymyxa (up to 2 nmol C2H4 h-1 mL-1) alone. To establish to what extent each partner contributed to nitrogenase activity, acetylene reduction was assayed as a function of time and it was also measured on Azospirillum cultivated in the cultures filtrates of the Bacillus. The results suggested that the nitrogenase activity was mostly produced by Azospirillum. The nitrogenase activity occurred at the expense of the degradation and fermentation products of the pectin. The new pectinolytic species, Azospirillum irakense, utilized both degradation and fermentation products of pectin, whereas the nonpectinolytic strains (Azospirillum brasilense, Azospirillum lipoferum, Azospirillum amazonense) utilized only the fermentation products of pectin, including acetic and succinic acids. These cocultures can be considered as metabolic associations, where the Bacillus produces degradation and fermentation products of pectin, which can be used by Azospirillum species.

Phytohormone-like substances produced by single and mixed diazotrophic cultures of Azospirillum and Arthrobacter

The production of phytohormone-like substances byAzospirillum brasilense andArthrobacter giacomelloi were investigated in single and mixed batch cultures under diazotrophic conditions. The mixed culture showed higher productivity of gibberellins and cytokinins.

Nitrogen fixation and indole acetic acid production by Azospi‐rillum sp. as influenced by an insecticide, carbofuran

Both indole acetic acid (IAA) accumulation and nitrogen fixation were increased in Azospirillum cultures isolated from rice roots and soils by carbofuran (2, 3‐dihydro‐2, 2‐dimethyl‐7‐benzofuranyl‐N‐methyl carbamate), an insecticide widely used in rice cultivation. Addition of carbofuran at 5 and 10 parts/106 significantly stimulated nitrogen fixation in Azospirillum. Indole acetic acid accumulation by Azospirillum cultures was more pronounced at a lower level (250 g/50 ml) of carbofuran. Evidence is provided for carbofuran degradation by Azospirillum cultures. The 7‐benzofuranol (2, 3‐dihydro‐2–2‐dimethyl‐7 benzofuranol), a major degradation product of carbofuran, however, did not enhance the IAA accumulation. The higher accumulation of IAA in Azospirillum in the presence of carbofuran is probably related to the increased growth due to fixed N present in the insecticide. Results indicate the involvement of parent compound carbofuran and/or compounds other than the 7‐benzofuranol in the higher accumulation of IAA by Azospirillum sp.

Nitrogenase activity in mixed cultures of Azospirillum with other bacteria

Summary Department of General Microbiology, Institute of Microbiology, Federal University of Rio de Janeiro, Brazil Fifty Gram-negative and 29 Gram-positive bacteria were tested in co-cultures in nitrogen-free, semisolid medium with either Azospirillum brasilense Sp7 or Azospirillum lipoferum Br17. Among the 79 bacteria examined, 12 Gram-negative and 7 Gram-positive did not exert any effect on the nitrgenase activity either in A. brasilense or A. lipoferum. The other bacteria stimulated or inhibited the nitrogenase either in one or both Azospirillum species. In several cases the same accompanying bacterium affected in a different way the two species of Azospirillum tested, stimulating one and inhibiting the other or acting on one, but not affecting the other. The active factors, produced by the accompanying bacteria, seem to be of oligodynamic nature. The capacity of producing these factors seems to be an individual pattern of particular strains, and no correlation was found between the taxonomical position of the accompanying bacterium and its manner of affecting Azospirillum.

Characterization of a substance produced by Azospirillum which causes branching of wheat root hairs

Previous studies have shown that Azospirillum or its culture filtrates induce root hairs in wheat seedlings to branch; this phenomenon is influenced by the bacterial genome at the strain level and by the plant genome at the cultivar level. Strain Sp245 caused most branching of root hairs; between wheat cultivars frequency of branching increased in the following order: cv. Tobari, cv. Tonari, cv. BH1146, cv. Lagoa. Similarly, plant growth response to inoculation with Azospirillum, measured in mature plants, increased in the same order, suggesting that both phenomena (root hair branching and plant growth response) have a similar basis. In this study, the "branching substance" present in Azospirillum culture filtrate was found to be thermostable at 100 °C, removed by dialysis, present in the acidic nonpolar fraction of the cell-free extract, and co-chromatographed with authentic indole acetic acid on thin-layer chromatograms. Purified indole acetic acid caused branching of root hairs similar to that caused by the Azospirillum culture filtrates. Susceptibility of wheat cultivars to indole acetic acid induced branching increased in the order: cv. Tobari, cv. Tonari, cv. BH1146, cv. Lagoa. Of five strains examined, strain Sp245 produced the most indole acetic acid in culture in the presence of tryptophan. The presence of indole acetic acid was confirmed by gas chromatography – mass spectrometry.

Prevalence of Azospirillum spp. in the rhizosphere of tropical plants

Azospirillum cultures were isolated from the roots of a variety of tropical plants. Presumptive isolates from selective medium were identified by biochemical and serological methods. Forty-eight percent of the isolates were identified as A. lipoferum and the rest as A. brasilense, nir+ or nir−. All of the isolates tested exhibited at least one heat-labile antigen with one or more of the three whole-cell reference antisera. Isolates identified as A. lipoferum were very similar to the reference strain SP59, while those identified as A. brasilense showed a greater degree of antigenic and biochemical diversity. No cross-reaction was detected between the four reference antisera used and strains of Azotobacter beijerinckia, A. chroococcum, A. vinelandii, Azomonas macrocytogenes, and A. agilis.

Organic acid utilization, succinate excretion, encystation and oscillating nitrogenase activity inAzospirillum brasilense under microaerobic conditions

Oscillating nitrogenase activity in long lasting batch cultures ofAzospirillum brasilense ATCC 29145 is independent of the carbon source malate. With fumarate, succinate or pyruvate as sole carbon source nitrogenase activity is also oscillating. Cultivation in a medium with 20-fold the buffer concentration also results in oscillating nitrogenase activity. Nitrogen-fixing cultures ofAzospirillum brasilense ATCC 29145 excrete ammonia into the culture medium varying between 0.02 and 0.04 mM concentrations. This is not sufficient to cause a drop of nitrogenase activity inAzospirillum brasilense after the first maximum. During growth under nitrogen-fixing conditions with malate as carbon source, the cells excrete significant quantities of succinate into the culture medium. Cultures with only 0.05% malate reutilized the excreted succinate as soon as malate disappeared from the medium.

Influence of various soil factors on nitrogen fixation by Azospirillum spp

The influence of soil pH, redox potential and added organic matter on N 2-fixation by Azospirillum was studied. Application of rice straw to alluvial, laterite and acid-sulphate Pokkali soils under submerged conditions enhanced the population of N 2-fixing Azospirillum spp. An acid-sulphate saline soil of extremely low pH (3.2) harboured Azospirillum spp with appreciable N 2-fixing activity. Enrichment cultures originating from soils with low pH (<4.0) possessed lower N 2-fixing activity compared to cultures from soils with higher pH values (upto 6.6). Azospirillum cultures from soils that had undergone prolonged waterlogging showed lower N 2-fixing activity than cultures isolated from soils submerged for a few days. A relationship was shown between the in vitro N 2-fixing activity of Azospirillum cultures and the redox status of the soil samples; activity was high when the soil redox potential was between −50 to −150mV. The results show that the N 2-fixing activity of Azospirillum cultures is governed by fluctuations in soil redox potential, pH and organic matter.