Molecular characterization of soil bacteria for improving crop yield in Pakistan

Nine Gram - positive bacterial strains designated as RH-1 to RH-9 were isolated from legumes rhizospheric soil and characterized for plant growth promoting (PGP) activities in legume and cereal crops as well as detailed morphological, phenotypic and biochemical studies. The strains were identified using 16S rRNA gene sequencing and chemotaxonomic traits. Based on comparative analysis of 16S rRNA gene sequencing, the strains showed highest similarity (97.9-99.8%) to the genus Bacillus. In vitro growth promoting assay indicated that the strain RH-5 proved potential PGPR by solubilizing highest amount of inorganic P (141 μg mL^-1), positive for nifH gene (+) and produced indole acetic acid (IAA; 0.82 μg mL^-1) followed by strain RH-2. Phosphorus solubilization in broth culture was associated with significant drop in pH by the strain RH-5 from 7.0 to 4.8. These two strains were further evaluated for plant growth promotion in beans (mung bean; Vigna radiate, mash bean; Vigna mungo) and wheat (Triticum aestivium) under axenic condition. The strain RH-5 proved the best PGPR by increasing crops biomass and grains (wheat; 40-45%, beans; 50%) over un-inoculated control. The chemotaxonomic data (pre dominant menaquinone system: MK-7, DNA G + C content: 40-41 mol%, major cellular fatty acid: anteiso-C_15:0) also supported the affiliation of both strains to the genus Bacillus. Phenotypic characterization showed that the strain RH-5 tolerated temperature: 50°C, pH: 10 and NaCl: 9%. Phylogenic and genotypic analysis showed the association of strains RH-5 and RH-2 with genus Bacillus having single phylitic lines to Bacilus gibsonii and Bacillus subtilis.