Rhizosheath of sinai desert plants is a potential repository for associative diazotrophs.

Among 42 plant species representing the flora of north Sinai, two possessed sand grain sheath encasing the roots. They are Panicum turgidum Forssk. and Stipagrostis scoparia (Trin.and Rupr.) deWinter. Rhizosheaths, compared to surrounding free sand, accommodated higher population density of microorganisms including associative diazotrophs. Isolates secured belonged to the species of Bacillus circulans, Paenib. macerans (Bacillus macerans), Enterobacter agglomerans, Agrobacterium radiobacter and Chryseomonas luteola (Pseudomonos luteola). The rhizosheath potentiality in re-vegetating sand dunes and arid lands, through nitrogen fixation, plant-water relationship and root continuity for nutrient uptake, are discussed.

Effect of inoculation with n(2)-fixing spirilla and azotobacter on nitrogenase activity on roots of maize grown under subtropical conditions.

Inoculated and non-inoculated seedlings of maize were grown in fertile clayloam soils of Egypt and Belgium under subtropical conditions provided in a greenhouse. Acetylene-reducing activity and microbial counts were determined during a period ranging from 6 to 12 weeks after sowing. Irrespective of soil origin, N(2)-fixing spirilla and Azotobacter were common under maize cultivation. Inoculation resulted in a transitional increase in their numbers at early stages of growth. Nitrogenase activity was not detected in the rhizosphere of young plants. The maximum activities measured (81 to 1,436 nmol of C(2)H(4) g h) occurred close to the 50 to 70% silking stage. Inoculation with N(2)-fixing spirilla, particularly in Nile Delta soil, doubled the amount of N(2) fixed in a late period of growth (12 weeks), whereas inoculation with Azotobacter had no noticeable effect.

Microbiological examination of some Sudanese soils.

The composition of the microflora in different layers of four representative oil profiles of Sudan were studied. Counts of all types of microorganisms decreased significantly with depth in soil. Azotobacter, in particular, occurred in high densities; representative strains were isolated and studied for their different characteristics. Beijerinckia was detected as well, and a new method for the estimation of their numbers in pure cultures, based on the overlay agar technique, is described.

Cell morphology and flagellation of nitrogen-fixing spirilla.

Twenty isolates of N2-fixing spirilla were isolated from the rhizosphere of maize and sugar cane grown in Egyptian and Belgian soils. Electron microscopy distinguished two morphological groups. The first includes short and thick curved rods with an unipolar flagellum while cells of the second group are much longer with the typical appearance of spiral cells and most probably possess a bipolar tuft of flagella.

Ecological studies on Azotobacter in Egyptian soils.

The present survey includes 156 representative soil samples. Results obtained confirm the richness of Egyptian soils, particularly the Nile Valley soils, in Azotobacter (60% of the samples contained greater than 10(3) colonies/g soil). Colony counts were lower than MPN estimations. Glucose is recommended for use in plating medium. Among the environmental factors affecting Azotobacter densities in soils of Egypt are: organic carbon content, total soluble salt content, pH and type of the soil, depth, cultivation, and standing crop. Pot experiments performed indicated that high incubation temperature (30, 37 degrees C) markedly enhanced development of Azotobacter as well as the gains of total nitrogen, particularly when soils are amended with 1% maize straw and incubated for 12 months. A. chrococcum was the most prevalent speciee; A. vinelandii was encountered as well. The analysis of some samples, representing soils of near Middle Eastern as well as North African countries, indicated the common occurrence of Azotobacter in these soils. Beijerinckia could not be detected in any of Egyptian or non-Egyptian samples examined.

The Azotobacter flora of some Czechoslovakian watercourses.

The occurrence of Azotobacter in some Szechoslovakian watercourses has been investigated. Several strains belonging to A. chroococcum and A. beijerinckii were isolated from 7 out of 18 samples. A. insignis has been isolated from the flowing water of Lake Machovo at Doksy. This is first report of this strictly aquatic Azotobacter species in Czechoslovakian watercourses. The taxonomy of the genus Azotobacter was discussed against the background of the existing knowledge resulting mainly from other taxonomic techniques than those based on the phenotypically expressed characters.