الفهرس 
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Abstract
The toxic effects of heavy metals in soil environments are a matter of increasing concern. Within soil are numerous species that are important in a number of biogeochemical cycles. Many soil species, in particular the streptomycetes, are responsible for the recycling of carbon locked in polymeric materials such as plant matter, and their activity is crucial to soil fertility. Therefore, an understanding of the response of these bacteria to heavy metals is timely.
The genus streptomyces comprises a large group of soil bacteria, which play important role in biodegradation, production of bioactive compounds as antibiotics and enzymes or in useful biological processes as waste treatment.
The current study has been performed on collection of soil samples by two ways. The first one, which considered to be polluted with some heavy metals from agriculture soils near the traffic road at Alexandria, Behera, Dakahlia and Ismaelia as well as from soils near to factories at Shubra El Kheima and Helwan. The second, from agriculture soil at Dakahlia under stress of different concentration of heavy metals.
Two concentrations of Cu and Zn sulphate solution (200 and 2000 µg.g-1) were added to the soil and samples were taken after 1, 4 and 12 weeks. The serial dilution method was used for isolation of streptomycetes. Four agar media were used for isolation as follow: starch nitrate agar, malt-yeast extract agar, inorganic salt starch agar and glycerol – L –asparagine agar. 0.1 ml inoculum of the proper dilution is spread on the surface of each plate of medium. The plates were incubated at 28° C for 7-14 days to allow the development of slow growing forms. All possible streptomycete colonies were isolated based on their special morphological characteristics and subjected for purification.
The streptomycete isolates were screened for their ability to resist the three different heavy metals (Cu, Zn and Pb) with six different concentrations (25, 50, 100, 150, 200 and 250 mM) and detected the minimum inhibition concentration (MICs) of each streptomycete isolate.
Isolation of streptomycetes using the four different isolation media from various collected samples revealed the presence of 546 isolates, from which 68 showed high resistances to heavy metals.
The active isolates of streptomycetes having high MICs were characterised in detail by cell and colony morphological features, biochemical and physiological and chemotaxonomic properties. Based on the phenotypic characters, numerical analysis was performed. Similarity calculations were made by the simple matching coefficient and clusters generated using the UPGMA-method.
Based on numerical analysis of phenotypical data supplemented and by using the determinative keys, different Streptomyces species were identified. In case of streptomycete isolates which subjected to different sources of heavy metals, the numerical analysis resulted that 20 different clusters having 12 single member phenon. The dominant streptomycetes was Streptomyces badius. Besides, Streptomyces anulatus, Streptomyces exfoliatus, Streptomyces chattanoogensis, Streptomyces albus, Streptomyces griseoflavous, Streptomyces rochei, Streptomyces halstedii, Streptomyces microflavus, Streptomyces albidoflavus, Streptomyces viridodiastaticus, Streptomyces pactum, Streptomyces viridochromogenes, Streptomyces cyaneus, Streptomyces aureofacienes, Streptomyces misakiensis, Streptomyces violaceus, Streptomyces acrimycini, Streptomyces violaceusniger and Streptomyces longisporoflavus species were also identified. The numerical analysis of streptomycetes isolated after addition of heavy metals with different concentration and time resulted that 12 different clusters having 8 single member phenons. The dominant streptomycetes was Streptomyces anulatus. Besides, Streptomyces rochei, Streptomyces acrimycini, Streptomyces bodili, Streptomyces halstedii, Streptomyces violaceusniger, Streptomyces diastaticus, Streptomyces cyaneus, Streptomyces violaceus, Streptomyces tanashiensis, Streptomyces exfoliatus and Streptomyces badius species were also identified.
By using selected different species of identified Streptomyces that showed high resistance to heavy metals (Cu, Zn and Pb) in uptake of them it was found Streptomyces viridochromgenes showed the maximum copper uptake (306.8 Cu µg/g biomass), while Streptomyces aureofacienes showed the maximum zinc uptake (734.8 Zn µg/g biomass) and the maximum lead uptake was detected with Streptomyces violaceusniger (576.2 Pb µg/g biomass).