Browsing by Author "Yaacov Okon"

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    Aerotaxis and Chemotaxis of Azospirillum brasilense: A Note
    (1980) Yaacov Okon; Lutfu Cakmakci; Israel Nu; Ilan Chet
    Azospiritlum brasilense was attracted to capillaries containing either phosphate buffer, distilled water, or saline. The number of bacteria in these capillaries was 3-4 X 10^4, after 1 h of incubation, [n the presence of phosphate buffer + attractants, the number of cells accumulated in the capillary increased only to5x 10^4-I.I x 10^5 cells. It was not possible, therefore, to measure chemotaxis in A. 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, arabinosc and galactose
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    Azospirillum as a potential inoculant for agriculture
    (1985) Yaacov Okon
    Azospirillum sp. contribute to increased yields of cereal and forage grasses by improving root development in properly colonized roots, increasing the rate of water and mineral uptake from the soil, and by biological nitrogen fixation. A better understanding of the basic biology of the Azospirillum root interaction, aided by the application of genetic engineering techniques, may lead to greater efficiency in its use as a bio-fertilizer.
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    Azospirillum: physiological properties, mode of association with roots and its application for the benefit of cereal and forage grass crops
    (1982) Yaacov Okon
    The free-living nitrogen-fixing bacterium Azospirillum species formerly known as Spirillum lipoferum (Beijerinck) has been described in detail by Tarrand et al., 1978. Based on DNA homology studies, two species of the genus have been characterized: Azospirillum brasilense and A. lipoferum. DNA composition of the genus is 69—71% G + C. The colonies are pink-red, drying out and turning rough with folded, wavy surfaces. Cells of Azospirillum are highly motile, half curved (vibroid), gram negative rods, having a diameter of 1.0 tan, with a polar flagellum when grown on liquid medium. Lateral flagella with shorter wavelengths could be observed in A. brasilense growing in agar medium. Cells contain prominent intracellular granules of poly-beta-hydroxybuty rate.
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    Methods for Growing Spirillum lipoferum and for Counting It in Pure Culture and in Association with Plants
    (1977) Yaacov Okon; Stephan L. Albrecht; Burris, R.H.
    Methods are described for growing Spirillum lipoferum in quantities sufficient to serve as inoculant in field trials of its associative N2-fixing ability with higher plants and as a source of cells for the preparation of nitrogenase, cytochromes, respiratory enzymes, etc. A heavy inoculum ot'S. lipoferum grown on NH4+ was transferred to a medium of minimal nitrogen content, and initial rapid growth at the expense of residual combined nitrogen was replaced later by slower growth on N,. Conversion to N; fixation was prompt upon exhaustion of fixed nitrogen; growth on N: was most rapid at a pO2 of 0,005 to 0.007 atm. Numbers of 5. lipoferum can be estimated by diluting soil, crushed roots, or other material, and inoculating diluted samples into a stagnant semisolid medium. Development of a characteristic subsurface layer of organisms and demonstration the these organisms can reduce C2H2 are presumptive evidence that they are S. lipoferum. With most-probable-number tables the observations can be converted to numbers of S. lipoferum in the samples. The rnost-probable-number method indicated that numbers of S. lipoferum may increase 100-fold or more in roots of maize removed from the plant and incubated for 24 h at 30°C at a pO2 initially adjusted to 0.01 atm.