Isolation of phosphate solubilizing bacteria from different medicinal aromatic plants and identification using MALDI TOF MS

Phosphate-solubilizing bacteria, which are among the plant growth-promoting bacteria, dissolve insoluble phosphate in the soil by several pathways and promote plant growth. Therefore, it offers an alternative option instead of applying chemical fertilizers that disrupt soil chemistry and ecological balance. Although research on phosphate solubilizing bacteria has increased recently, the research on the peppermint and fennel rhizosphere is still limited. Investigating different rhizospheric local bacteria that can solubilize phosphate and replace chemical fertilizers is necessary. It was determined that 15 of the 53 bacterial isolates obtained from peppermint (Mentha piperita L.) and fennel (Foeniculum vulgare L.) rhizospheres formed a transparent (halo) region around the colonies on Pikovskaya Agar (PKA) medium using the MALDI-TOF MS method. The morphological, biochemical and IAA production of these isolates as well as quantitative measurements of phosphate solubilization by the isolates in NBRIP broth medium was evaluated. The highest efficiency was noted from Bacillus subtilis MMS-7 with solubilization value of 281.6 mg L-1. This was followed by Pseudomonas fluorescens MMS-11 with solubilization value of 263.4 mg L-1 and Bacillus thuringiensis MMS-3 with solubilization value of 172.1 mg L-1, respectively. Among the Phosphate solubilizing bacterial isolates, P solubilization index ranged 1.2-3.7 on PKA agar medium. Additionally, the highest IAA production was noted at 23.38 µg ml-1, using Bacillus subtilis MMS-7. This was followed by Pseudomonas fluorescens MMS-11 with value of 19.72 µg ml-1 and Bacillus thuringiensis using MMS-3 with value of 18.98 µg ml-1. This study demonstrated that selected local isolates can be used as effective phosphate-based microbial fertilizers.