Characterization of phosphate solubilizing bacteria and nitrogen fixing bacteria from limestone mining region

ABSTRACT

Aims: Phosphate and nitrogen are major macronutrients needed by plants. Phosphates in the soil are present in the organic and inorganic form. The amounts of phosphate and nitrogen in marginal soil can be increased by plant growth promoting rhizobacteria (PGPR). The aim of this study was to isolate and characterize phosphate solubilizing bacteria which has ability to fix nitrogen from the soil around limestone mining area. Methodology and results: There were 22 isolates that could solubilize phosphate and fix nitrogen. There were 9 isolates that could not cause hypersensitivity symptoms (necrotic) on tobacco leaf. Quantitative assay of phosphate solubilizing was done by colorimetric method. Quantitative assay of phosphate showed that isolate GPC1.7 had the highest phosphate solubilizing activity on Pikovskaya broth (450 mg/L) on the 6th and 7th day of incubation whereas isolate GPA2.2 had the highest nitrogen fixing activity (0.162 ppm/h), measured with Acetylene Reduction Assay whereas nitrogenase activity of GPC1.7 was unidentified. Isolate GPA2.1 and GPA2.2 were Gram negative bacteria whereas isolate GPC1.7 was Gram positive bacteria. Identification based on 16S rRNA gene showed that GPA2.1 was closely related to Pseudomonas psychrotolerans, GPA2.2 was closely related to Stenotrophomonas maltophilia, GPC1.7 was closely related to Bacillus megaterium and B. aryabhattai. Conclusion, significance and impact of study Phosphate solubilizing bacteria and nitrogen fixing bacteria isolate could be further used for revegetation process of the ex-limestone mining area.