Plant growth promoting properties of phosphate solubilizing Bacillus species isolated from the Aegean Region of Turkey

Bacillus species, due to their soil amendment properties, are important members of plant-growth-promoting rhizobacteria (PGPR). In this study, with the aim to discover potential biofertilizers, 440 Bacillus isolates from different sources were screened qualitatively for phosphate solubilizing and positive isolates were processed for quantitative estimation of solubilized phosphate and organic acid production. Organic acid production was initially detected by pH change of the media, whereas further confirmation and quantitative estimation were done by gas chromatography (GC). The results indicate that phosphate solubilization ranges from 6.9 ± 1.00 to 95.5 ± 1.83 µg mL − 1 " role="presentation"> − 1 for Bacillus isolates and most of the isolates were able to produce more than one organic acid in substantial quantities range between 70.70 ± 1.90 and 619.20 ± 1.40 (ng µL − 1 " role="presentation"> − 1 ). Correlations among total organic acid concentration, final pH of the media, and soluble phosphate were statistically calculated. The six best phosphate-solubilizing isolates were further tested for indole-3-acetic acid (IAA) production, molecular identification, in vitro seed germination, and pot trials. All six strains produced IAA, significantly enhanced radicle and hypocotyl development, and considerably increased plant growth by improving growth of roots and stems. On the basis of results, these Bacillus strains can be considered as potential biofertilizers.