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  • 1
    Electronic Resource
    Electronic Resource
    Counting viableAzotobacter chroococcum in vertisols (1989)
    Springer
    Plant and soil 117 (1989), S. 9-16 
    Details
    ISSN: 1573-5036
    Keywords: Azotobacter chroococcum ; chemical dispersion ; counting ; cracking clays ; diluents ; enumeration ; glass beads ; mechanical disaggregation ; mineral salts ; osmotic protectants ; saline ; coarse sand ; shaking period ; suspensions ; vertisols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Methods for preparing soil suspensions for countingAzotobacter chroococcum in vertisols by soil dilution and plating were investigated. Mechanical methods to promote disaggregation of soil and Azotobacter microcolonies by shaking soil suspensions with glass beads (10% w/v) or coarse sand (1–2 mm fraction) increased soil dispersion and Azotobacter colony counts. Chemical methods for disaggregation were unsatis-factory. The non-ionic detergent ‘Agral’ (0.004, 0.02, 0.1, 0.5 and 2.5% w/v) had no significant effect on soil dispersion and Azotobacter count. Both sodium pyrophosphate (0.03, 0.1, 0.3 and 0.9% w/v) and sodium metaphosphate as ‘Calgon’ (0.022, 0.066, 0.2, 0.6 and 1.8% w/v) increased soil dispersion but were toxic to Azotobacter. Increasing time of shaking soil: distilled water suspensions increased deflocculation of the clay and Azotobacter counts to a maximum after 6–23 hours shaking. Comparable results were obtained within 30–60 minutes of shaking with coarse sand, but shaking with coarse sand beyond 2 hours reduced counts through mechanical damage to cells. Counts from suspensions in physiological saline (0.75% NaCl) and in distilled water were similar. Counts from suspensions in Jensen's mineral base shaken for 〈3 hrs were lower than from distilled water due to flocculation fo the soil byCa2+ ions, but were higher on extended shaking up to 23 hours due to better cell protection. Shaking soil suspensions in distilled water with 10% w/v coarse sand for 30 minutes is recommended when counting Azotobacter in vertisols.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02206252
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  • 2
    Electronic Resource
    Electronic Resource
    Counting viableAzotobacter chroococcum in vertisols (1989)
    Springer
    Plant and soil 117 (1989), S. 17-29 
    Details
    ISSN: 1573-5036
    Keywords: Azotobacter chroococcum ; counting ; cracking clays ; enumeration ; media ; vertisols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Counts of Azotobacter on Brown's medium containing 0.5% glucose sterilized separately from phosphates were greater than on some 20 other published media and modifications. Brown's medium gave considerably greater counts than Rovira's combined carbon medium, but pigmentation ofA. chroococcum allowing ready identification was more developed on the latter. Addition of components of Rovira's medium to improve pigmentation in Brown's medium was only partly successful. With Ca acetate+Na citrate as C sources, percentage pigmented colonies was increased from 0 to 85% but colony counts were lower than with glucose. Sucrose as carbon source resulted in larger colonies but lower counts. In an experiment with nine published media plus eleven modifications comprising carbon sources of glucose, sucrose, arabinose, dextrin, mannitol, acetate, citrate, and benzoate in various mineral bases, Brown's medium gave greatest counts. Counts on other media were increased to comparable levels by substituting separately sterilized 0.5% glucose for original carbon sources. Other media like Rovira's, Parker's and Aleem's had greater percentages of pigmented colonies with Aleem's benzoate medium having the most intensely pigmented colonies. Mineral composition had little effect on colony counts. Density of oligonitrophilic bacteria on the various media had little effect on counts of Azotobacter. Multiple regression analyses were used to relate Azotobacter colony counts and characteristics to 22 organic and inorganic constituents of media. Counts were positively related to glucose sterilized separately and negatively related to sucrose. Colony diameter was positively related to sucrose. Percentage of pigmented colonies was positively related to Ca, glucose and benzoate and negatively related to Ca/Na ratio and S. Non-pigmented Azotobacter colonies on Brown's medium became pigmented when replica-plated to other media indicating all wereA. chroococcum. Brown's medium is recommended for counting Azotobacter in vertisols with replica plating to a chromogenic medium,e.g., Rovira's, for identification ofA. chroococcum if required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02206253
    Location Call Number Limitation Availability
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Counting viable Azotobacter in vertisols (1989)
    Springer
    Plant and soil 117 (1989), S. 31-40 
    Details
    ISSN: 1573-5036
    Keywords: Azotobacter chroococcum ; counting Azotobacter ; cracking clays ; enumeration of ; Azotobacter, soil dilutions for counting Azotobacter ; non-proportionality in Azotobacter counts ; vertisols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In counting Azotobacter in vertisols by the soil dilution and spread-plating method, mean colony counts/plate did not decrease in proportion to the dilution factor and consequently derived counts of Azobacter cells/g soil decreased with increasing dilution of the soil suspension. This non-proportionality phenomenon was analysed in several experiments with six soils. Conformity to the Poisson distribution for counts on parallel plates was measured by Fisher's index of dispersion (χ2), which proved too high (P〈.05) at lower dilutions, indicating inaccurately low mean colony counts. At highest dilutions, proportional errors increased resulting in less precise estimates of means, because with a Poisson distribution the standard deviation is equal to the square root of the mean, and the multiplication factor for derived counts/g soil is greatest at highest dilutions. By varying both plate surface area and dilution factor, results indicated that the non-proportionality phenomenon is caused by crowding at lower dilutions increasing the probability of colony coincidence on the plates. Graphical analysis of results of several dilution series indicated that derived counts are best based on dilutions giving 10–40 colonies/9 cm diameter plate, which is best achieved from two-fold dilution series.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02206254
    Location Call Number Limitation Availability
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    Paper (German National Licenses)
    Fulltext
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