Isolation and characterization of diazotrophic growth promoting bacteria from rhizosphere of agricultural crops of Korea

Free-living nitrogen fixing bacteria were isolated from rhizosphere of seven different plant namely sesame, maize, wheat, soybean, lettuce, pepper and rice grown in Chungbuk Province, Korea. Five isolates with nitrogenase activity above 150 nmol h−1 mg−1 protein were identified based on phenotypic and 16S rDNA sequences analysis. The strains were identified as Stenotrophomonas maltophilia (PM-1, PM-26), Bacillus fusiformis (PM-5, PM-24) and Pseudomonas fluorescens (PM-13), respectively. All the isolates produced indole-3-acetic acid (IAA), in the presence of tryptophan, ranging from 100.4 μg ml−1 (PM-13) to 255 μg ml−1 (PM-24). The isolate PM-24 (Bacillus fusiformis) exhibiting highest nitrogenase activity (3677.81 nmol h−1 mg−1 protein) and IAA production (255 μg ml−1) has a promising potential for developing as a plant growth promoting rhizobacteria.