A growth-promoting monocrotophos tolerant Klebsiella pneumoniae subsp. ozaenae SK1 isolated from the phyllosphere of Ricinus communis exhibit potential for biofertilizer in pesticide-contaminated soil

The phyllosphere provides a unique group of microorganisms that influence plant functions and overall growth and development. Pesticide application may influence the microbial population of the phyllosphere and disrupt the delicate balance of microbial diversity and species composition of the phyllosphere. The present investigation focuses on the isolation of cultivable bacteria inhabiting the leaf surface of Ricinus communis and explores their potential to tolerate or degrade monocrotophos. Twenty-six morphologically distinct bacterial isolates were retrieved from both the abaxial and adaxial surfaces of the leaf using the leaf imprint technique. Isolates R-9, R-13, R-15, R-21, R-32, and R-34, showed tolerance to 25 ppm of monocrotophos as evidenced by enhanced growth in Minimal Salt Medium (MSM) containing pesticide as the only source of carbon. Isolate R-9 was further selected based on its better growth in the presence of pesticide among the selected isolates and identified as Klebsiella pneumoniae subsp. ozaenae SK1 with 99.86% sequence similarity as determined through 16S rRNA gene sequencing. The selected isolate showed tolerance for monocrotophos up to 500 ppm on MSM agar plate and up to 200 ppm in liquid culture medium with the highest growth in 100 ppm. The isolated strain exhibited significant emulsification along with plant growth-promoting activity in the presence of 100 ppm of monocrotophos. Overall, the pesticide did not affect the plant growth-promoting activities and other physiological enzymes of Klebsiella pneumoniae ozaenae SK1. Hence study indicates that the isolated strain Klebsiella pneumoniae subsp. ozaenae SK1 from leaves of Ricinus communis may be used for enhancing plant growth and development in pesticide-contaminated soil environments.