Abstract
To develop an osmotolerant microbe, as a bioinoculant to mitigate drought it is vital to understand the impact of osmotic stress on their growth and plant growth promoting functional traits. The present study was aimed to evaluate the physiological adaptations and plant growth-promoting traits of a phyllosphere bacterium Bacillus altitudinis FD48 under osmotic stress conditions. The FD48 strain isolated from rice (cultivar ADT43) phyllosphere obtained from Biocatalysts laboratory, Department of Agricultural Microbiology, Tamil Nadu Agricultural University, Coimbatore. In vitro bioassay was conducted to evaluate the osmotolerant potentials of FD48. B. altitudinis FD48 grown in LB supplemented with PEG 6000 and grown for 48 hrs. Physiological adaptation to osmotic stress was observed by assessing the osmolytes and free amino acids content produced by FD48 under induced stress. Further the plant growth promoting traits under osmotic stress also asceratined. The growth pattern of FD48 strain decreased with the increase in PEG concentrations. The lower level of osmotic stress enhanced the growth of FD48 but at higher concentration exhibited a decline in growth. Enhanced levels of IAA (25 µg g-1 of protein) and EPS (9.76 mg mg-1 protein) production were recorded in the FD48 strain at lower levels of osmotic stress. Furthermore, an increase in osmotic stress had a deleterious effect on IAA production and ACC deaminase activity while the exopolysaccharide production was enhanced. Growth of FD48 under osmotic stress also increased the accumulation of proline and compatible sugars that will protect the FD48 strain by maintaining the turgor potential of cells and stabilizes the membrane proteins. Hence, the results of our study suggesting that, B. altitudinis FD48 strain has the potential to tolerate osmotic stress and might be used as a newer bio-inoculant for triggering moisture deficit stress resilience in plants.
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