SOME PLANT GROWTH PROMOTING TRAITS OF STREPTOMYCES SPECIES ISOLATED FROM VARIOUS CROP RHIZOSPHERES WITH HIGH ROOT COLONIZATION ABILITY OF SPINACH (SPINACIA OLERACEA L.)

Streptomyces species a genus in Actinobacteria phylum were isolated from the rhizosphere of some plants in Los Angeles. Some plant growth promotion properties of isolates were determined, such as: indole acetic acid, siderophore production and phosphate solubilization. The colonization ability of Streptomyces species was investigated under in vitro conditions on spinach seeds. Maximum likelihood approach was applied to 16S rRNA gene sequences to draw a phylogenetic tree of the best identified isolates, according to their measured properties. A total of ten isolates were characterized as Actinobacteria according to their morphological properties. Of those, four isolates possessing some traits related to plant growth promotion were identified as Streptomyces griseus strain 52-1 (Step1) and Streptomyces albogriseolus strain DSM 4 (Step-2) from tomatoes, Streptomyces aurantiacus strain 4683 (Step-5) and Streptomyces kanamyceticus strain 22-5 (Step-8) from sunflowers' rhizosphere. The identified isolates showed the maximum indole acetic acid production, 95.67, 110.14, 94.12 and 105.04 mg L-1, respectively. The maximum siderophore production (22.23, 19.34, 10.12 and 33.24 mg mL(-1)) and mineral phosphate solubilization (61.8, 69.32, 61.6 and 68.4 mg 100 mL-1) were obtained using Strep-1, Strep-2, Strep-5 and Strep-8 isolates, respectively. None of the isolates could grow on nitrogen free media. The results of spinach root colonization test with the isolates indicated the potential of Strep-1, Strep-2, Strep-5 and Strep-8 isolates to colonize spinach roots.