Counting viableAzotobacter chroococcum in vertisols

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 by^Ca2+ 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.     

Studies on sulphur in vertisols

Summary Some soil and plant test methods were evaluated for predicting response of soybean crop (Glycine max (L.) Merr.) to S application in vertisols. Morgan's reagent, 500 ppm P containing Ca(H₂PO₄)₂.H₂O and KH₂PO₄ solutions, 0.5N NH₄OAc+0.25N HOAc and 0.15% CaCl₂ were found to be suitable extractants for measuring available soil S. The critical limits of extractable S were 9.0 ppm by Morgan's reagent, 10.0 ppm by phosphate solutions, 8.0 ppm by 0.5N NH₄OAc +0.25N HOAc and 14.0 ppm by 0.15% CaCl₂. Morgan's reagent was regarded as superior to other soil test methods in view of its high relationship with S uptake by plants, A values and relative yield. Critical S concentration in soybean plants varied with age. It was 0.15% and 0.185% for 36 and 60 days old plants, respectively. The critical N/S ratio on the other hand appeared to be constant at about 16.5 during vegetative growth period. Constancy of critical N/S ratio in plants was attributed to the near constancy of N/S ratio in plant proteins. There was highly significant relationship between response of soybean to S and to N, supporting the conclusion of some earlier workers that any soil showing large responses to N may not be supplying adequate S from the mineralization of soil organic matter.     

Understanding zinc reactions in vertisols to predict zinc responses by wheat

Since Zn availability to plants growing in a soil is governed by quantity, intensity, buffer power, rate of Zn desorption and diffusion, an improved understanding of a number of these factors in Vertisols would facilitate a more reliable prediction of crop requirements for Zn. The DTPA-extractable Zn, a quantity factor, together with initial Zn desorption rate coefficients, accounted for 80% of the variation in relative dry matter yield of wheat grown to anthesis. In combination with these factors, desorption (buffer) power explained 92% of the variation in Zn concentration in the young mature leaf blade (YMB) of wheat. Thus, the combination of the quantity, rate of Zn desorption and buffer power better predict growth responses of wheat to applied Zn in Vertisols than the commonly-used single extraction with DTPA alone (quantity), which provides only a static measure of Zn availability.     

Counting in oogenesis

The determination of a precise number of cells within a structure and of a precise number of cellular structures within an organ is critical for correct development in animals and plants. However, relatively little is known about the molecular mechanisms that ensure that these numbers are achieved. We discuss counting mechanisms that operate during ovarian development and oogenesis.     

Derepression of nitrogenase in Azotobacter

When nitrogenase in $\text{Azotobacter vinelandii}$ 12837 is repressed by ammonia, the derepression is accelerated by endotoxin or cyclic AMP. The phenomenon appears neither to be a consequence of accelerated ammonia utilization nor altered activity of preformed enzyme. This is a unique example of an effect of endotoxin on a procaryotic system.     

Nitrite uptake in Azotobacter chroococcum

Nitrite uptake is made up of two components in Azotobacter chroococcum, a passive diffusion, presumably of nitrous acid, and an active transport of nitrite which uses the nitrate transport system. Only the active component is under regulatory control.     

Azotobacter bacteriophages in Czechoslovakian soils

Summary Azotobacter bacteriophages were studied using liquid as well as solid enrichment cultures. The study included 16 samples representing the soils of Ruzyn, Prague. The effect of long-term application of mineral fertilizers (N, P, K) and organic manure (straw enriched by inorganic nitrogen) to the soil on Azotobacter and their phages was investigated. Liquid enrichments yielded phages in fairly high titers, and phages were found in most of the soils while solid ones only gave low titers in occasional soils. On the basis of plaque morphology 4 different phage types were obtained. Electron micrographs showed that the phages belong to the groups with long non-contractile, contractile, and short contractile tails. Host specificity assay showed that the majority of the strains of A. chroococcum, A. vinelandii, and one strain of A. beijerinckii were lysed by phage, while none of A. macrocytogenes, A. agilis and A. insignis strains were lysed. Phage inactivation and neutralization was carried out with homologous antisera. re]19741128     

Indole derivatives in Azotobacter cultures

В культурах азотобактера и его почвениых препатах содержатся ?изиологически активные вещества, частькоторых термостабильна. Количество ?изиологически активных веществ зависит от штамма азотобактера и от возраста культур. Особое внимание посRящалось гетероауксину. С помощью разделительной хроматогра?ии на бумаге и биологического теста было доказано присутствие β-индолуксусной кислоты и еще однго, пока не иденти?ицированног о, ?акгора роста. β-индолуксусная кислота в старых культурах превращается в индол-З-карбоновую кислоту. Полученные результаты обсуждаются с точки зрения влияния культур азотобактера на рост растений.     

Beta-ketothiolase genes in Azotobacter vinelandii

Azotobacter vinelandii is proposed to contain a single β-ketothiolase activity participating in the formation of acetoacetyl-CoA, a precursor for poly-β-hydroxybutyrate (PHB) synthesis, and in β-oxidation (Manchak, J., Page, W.J., 1994. Control of polyhydroxyalkanoate synthesis in Azotobacter vinelandii strain UWD. Microbiology 140, 953–963). We designed a degenerate oligonucleotide from a highly conserved region among bacterial β-ketothiolases and used it to identify bktA, a gene with a deduced protein product with a high similarity to β-ketothiolases. Immediately downstream of bktA, we identified a gene called hbdH, which encodes a protein exhibiting similarity to β-hydroxyacyl-CoA and β-hydroxybutyryl-CoA dehydrogenases. Two regions with homology to bktA were also observed. One of these was cloned and allowed the identification of the phbA gene, encoding a second β-ketothiolase. Strains EV132, EV133, and GM1 carrying bktA, hbdH and phbA mutations, respectively, as well as strain EG1 carrying both bktA and phbA mutations, were constructed. The hbdH mutation had no effect on β-hydroxybutyryl-CoA dehydrogenase activity or on fatty acid assimilation. The bktA mutation had no effect on β-ketothiolase activity, PHB synthesis or fatty acid assimilation, whereas the phbA mutation significantly reduced β-ketothiolase activity and PHB accumulation, showing that this is the β-ketothiolase involved in PHB biosynthesis. Strain EG1 was found to grow under β-oxidation conditions and to possess β-ketothiolase activity. Taken together, these results demonstrate the presence of three genes coding for β-ketothiolases in A. vinelandii.