Halotolerant Plant Probiotic Bacterial Isolates of Mangrove Soils of Chidambaram and Thanjavur, India

Halotolerant plant growth-promoting rhizobacteria (HTPGPR) are beneficial microbes that can be exploited to mitigate the negative effects of soil salinity on crops. In the current investigation, eight saline soil samples collected from 2 mangrove ecosystems of Tamil Nadu (Chidambaram and Thanjavur) during December 2022 were used to isolate saline tolerant bacterial cultures at the Department of Agricultural Microbiology, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India. Using 5 different bacterial growth media, 48 rhizobacterial isolates (ST1 to ST48) were obtained. Salt tolerance ability (0, 5, 10, 15 and 20% NaCl) of these 48 isolates under in vitro conditions indicated their potential to tolerate up to 10% NaCl (1.71 M). None of the isolates could grow at 20% NaCl (3.42M). Bacterial isolates such as ST11, ST13, ST18, ST20 and ST27 showed minimum growth at 15%NaCl (2.57M). 33 isolates which could grow well at higher salt concentrations were selected. Among 33 isolates, 18 isolates with higher concentration of intracellular sodium content (ST1, ST2, ST3, ST7, ST8, ST9, ST11, ST12, ST13, ST17, ST18, ST20, ST27, ST30, ST32, ST34, ST39, and ST40) were selected and characterized qualitatively for their ability to mineralize phosphate, potassium, and zinc, and to produce HCN. Potential of these18 bacterial isolates to tolerate other abiotic stress factors such as pH and temperature was also studied. Among 18 isolates, the isolates ST7, ST17, and ST30 were found to be multimineral solubilizers. Bacterial isolate ST17 was found to prefer alkaline (pH 9.0) and mesophilic temperature (35ºC) for its growth at both saline (5% NaCl) and non saline condition.