Israel Nur

Effect of Azospirillum inoculation on some growth parameters and n-content of wheat, sorghum and panicum

The potential of the nitrogen fixing bacteriumAzospirillum brasilense to enhance development and increase growth of several gramineae was investigated. In both sterilized and non-sterilized systems heading and flowering occurred earlier in the inoculated plants as compared to the noninoculated ones. Total shoot and root weights, total-N content, plant height and leaf length were significantly increased by inoculation.

Yield Increases in Summer Cereal Crops in Israeli Fields Inoculated with Azospirillum

Inoculating Zea mays (three cultivars), Sorghum bicolor, Panicum miliaceum and Setaria italica with nitrogen-fixing bacteria of the genus Azospirillum in Northern Negev and Bet Shean Valley field experiments resulted in significant increases in yield of grain and foliage of commercial value. It was concluded that inoculating summer cereal crops in Israel may save valuable nitrogen fertilizer.

Response of Non-irrigated Sorghum bicolor to Azospirillum Inoculation

In two experiments, carried out on non-irrigated fields in the Northern Negev region of Israel, inoculation of Sorghum bicolor with bacteria of the genus Azospirillum resulted in significant increases over controls of 17% in grain yield of cv. 610 and of 19% in the forage yield of cv. 6078. In addition, significant increases over controls in plant dry weight, mineral content (N, P and K) and panicle number were obtained by inoculation of cv. 610.

Carotenoid Composition and Function in Nitrogen-fixing Bacteria of the Genus Azospirillum

SUMMARY: Four different carotenoids were isolated and purified from membranes of the N2-fixing bacterium Azospirillum brasilense strain Cd, grown under aerobic conditions, and one from strain Cd-1. Carotenoid synthesis did not occur under microaerobic conditions. Cells of these strains formed aggregates (>0-1 mm in diameter) when subjected to aerobic conditions. Neither carotenoids nor cell aggregation were observed in A. brasilense strains Sp 7, Sp81 and Sp51e. All of the differently pigmented Azospirillum strains tested contained similar amounts of soluble cytochrome c. In the presence of diphenylamine, which specifically inhibits carotenoid synthesis, the rate of acetylene reduction (N2 fixation) in strain Cd decreased to 50% of the control. Carotenoid synthesis was inhibited in cells grown in the presence of NH4Cl at concentrations higher than 10 mM. Carotenoid synthesis started in liquid cultures of suain Cd only after the concentration of NH4Cl in the medium decreased, and N2 fixation became evident at the same time. In comparison, strain Sp81 did not grow or fix nitrogen after NH4Cl was depleted. Carotenoids appear to protect the nitrogenase of A. brasilense strains Cd and Cd-1 from oxidative damage.

Effect of Dissolved Oxygen Tension on Production of Carotenoids, poly-β-hydroxybutyrate, Succinate Oxidase and Superoxide Dismutase by Azospirillum brasilense Cd Grown in Continuous Culture

SUMMARY: Azospirillum brasilense strain Cd was grown in a medium containing NH4 + in a chemostat at a range of constant dissolved oxygen tensions (d.o.t.) (0·007--0·18 atm). Poly-β-hydroxybutyrate (up to 12% of the cell dry weight) increased under oxygen limitation and moderate dilution rate (D = 0·14 h-1). The highest carotenoid content was observed at high d.o.t. and dilution rates up to 0·12 h-1. The amount of protein varied with d.o.t. from 0·29 mg protein (mg dry wt)-1 at 0·007 atm to 0·54 mg at 0·18 atm. The yield efficiency and respiration rate were highest at low d.o.t. and decreased significantly at a d.o.t. of 0·18 atm. Succinate dehydrogenase and malate dehydrogenase activities increased 2·5-fold at 0·10-0·18 atm O2, whereas succinate oxidase and NADH oxidase activities increased consistently with increasing d.o.t. Azospirillum brasilense showed a low specific activity for catalase; the specific activity of superoxide dismutase increased sharply above 0·16 atm O2.

THE EFFECT OF AZOSPIRILLUM INOCULATION ON GROWTH AND YIELD OF CORN

ABSTRACT Commercial yields of sweet corn cv. Jubilee were increased by field inoculation with Azospirillum. This bacterium was found in association with grass roots in different soils all over the world. In field experiments carried out in several parts of Israel Azospirillum was shown to affect both vegetative and reproductive growth of corn at different levels of nitrogen fertilization. Effects on vegetative growth induded increase in plant height and fresh and dry weight of plant foliage. The effects on reproductive structures were expressed mainly via increase in ear number per plant. It was concluded that it may be possible partially to replace combined N fertilizer in corn by Azospirillum.

Free and integrated plasmid DNA in spiroplasmas

Spiroplasma citri was found to carry an 8.0 kb plasmid that differed from previously describedS. citri plasmids in its restriction map. It was also clonable in pBR322. The plasmid, named pRA1, was found in large quantities as free plasmid inS. citri (R8A2, Maroc) subclones of low passage level. In subclones of higher passage levels, free plasmid was replaced by plasmid sequences integrated into the spiroplasma chromosome. Significant quantities of integrated plasmid sequences were also observed in the corn stunt spiroplasma,S. kunkelii, while small quantities of free and/or integrated plasmid DNA could be detected in some spiroplasmas serologically and genotypically remote fromS. citri. Integrated plasmid sequences were cloned into theEscherichia coli plasmid pUC13. Hybridization tests and restriction maps of these clones indicated that the integrated plasmid sequences consisted of fragments, rather than entire plasmid DNA, inserted into specific sites in the spiroplasma chromosome. Although the biological role of the pRA1 plasmid remains unclear, theS. citri subclones containing large quantities of free plasmid exhibited slower growth rates and a tendency to lyse.

Aerotaxis and chemotaxis ofAzospirillum brasilense: A note.

Azospirillum brasilense was attracted to capillaries containing either phosphate buffer, distilled water, or saline. The number of bacteria in these capillaries was 3−4×104, after 1 h of incubation. In the presence of phosphate buffer + attractants, the number of cells accumulated in the capillary increased only to 5×104–1.1×105 cells. It was not possible, therefore, to measure chemotaxis inA. brasilense as distinct from aerotaxis by the capillary method. Chemotaxis was observed in semi-solid agar plates and was determined by a growth band oriented towards the attractant. Positive chemotactic response was obtained with peptone, tryptone, yeast extract, amino acids, organic acids, arabinose and galactose.

TACTIC RESPONSES OF AZOSPIRILLUM BRASILENSE TOWARDS OXYGEN AND ORGANIC COMPOUNDS

Azospirillum brasilense responded towards self-created oxygen gradients by forming aerotactic bands in capillary tubes and by actively moving towards a limited oxygen zone, optimal for their motility. Increasing oxygen concentration in capillaries containing phosphate buffer increased the number of bacteria attracted and decreased band velocity. High oxygen concentrations and H2O2 caused a temporary repulsion of the bacteria from the capillary mouth and formation of a highly motile bacterial arc around it. Exogenous sources of energy were not necessary for aerotaxis in Azospirillum. The aerotactic response of Azospirillum was not affected by the removal of the combined nitrogen from the growth medium. Substrates added to capillaries containing phosphate buffer increased the number of bacteria attracted only 1.2–3 fold. Chemotaxis in Azospirillum could not be measured using the capillary assay, but was examined using the agar plate method in which the aerotactic response was prevented.

THE ROLE OF OXYGEN CONCENTRATION IN THE SYNTHESIS OF CAROTENOIDS, POLY-β-HYDROXYBUTYRATE AND SUCCINATE OXIDASE IN CONTINUOUS CULTURE OF AZOSPIRILLUM

ABSTRACT The nitrogen fixing bacterium Azospirillum brasilense Cd was grown in ammonium-mineral salts medium in a chemostat, with malate as a growth-limiting carbon and energy source under various dissolved oxygen tensions (d.o.t.). Maximum poly-β-hydroxy- butyrate content (12% w/w of the biomass) was observed under microaerobic conditions (d.o.t. = 0.007 atm) and intermediate dilution rates (D = 0.14 h−1. In carbon-limited cultures (D = 0.008 h−1) cell yield and respiration in situ ranged from 48 to 62 g dry wt·(mole malate)−1 and from 75 to 325 μl O2 ·(mg protein)−1, respectively. Highest cell yield and respiration rate were obtained at relatively low concentration of oxygen (d.o.t. = 0.007 atm). Protein content of cultures was significantly higher at high oxygen levels. However, a rapid decrease was observed under lower oxygen levels. Succinate oxidase and succinate dehydrogenase activities were especially high under high oxygen concentration (d.o.t. > 0.1 atm). Four different carotenoids were isolated...