Characterization of Arsenic-Resistant Endophytic Bacteria From Alfalfa and Chickpea Plants.

The present investigation was carried out to isolate arsenic (As)-resistant endophytic bacteria from the roots of alfalfa and chickpea plants grown in arsenic-contamination soil, characterize their As tolerance ability, plant growth-promoting characteristics, and their role to induce As resistance by the plant. A total of four root endophytic bacteria were isolated from plants grown in As-contaminated soil (160-260-mg As kg of soil). These isolates were studied for plant growth-promoting (PGP) characteristics through siderophore, phosphate solubilization, nitrogen fixation, protease, and lipase production, and the presence of the arsenate reductase () gene. Based on sequence analysis, these isolates belong to the genera , and . All isolates were found As tolerant, of which one isolate, sp. QNC1, showed the highest tolerance up to 350-mM concentration in the LB medium. All isolates exhibited phosphate solubilization activity. Siderophore production activity was shown by only sp. QNC1, while nitrogen fixation activity was shown by only sp. QNC2 isolate. sp. QNA1, QNA2, and sp. QNC2 exhibited lipase production, while only sp. QNC1 was able to produce protease. The presence of the gene was detected in all isolates. The effect of endophytic bacteria on biomass production of alfalfa and chickpea in five levels of arsenic concentrations (0-, 10-, 50-, 75-, and 100-mg kg soil) was evaluated. The fresh and dry weights of roots of alfalfa and chickpea plants were decreased as the arsenic concentration of the soil was increased. Results indicate that the fresh and dry root weights of alfalfa and chickpea plants were significantly higher in endophytic bacteria-treated plants compared with non-treated plants. Inoculation of chickpea plants with sp. QNC1 and sp. QNC2 induced lower gene expression in chickpea roots grown in soil with the final concentration of 100-mg kg sodium arsenate compared with the non-endophyte-treated control. The same results were obtained in sp. QNA2-treated alfalfa plants grown in the soil plus 50-mg kg sodium arsenate. These results demonstrated that arsenic-resistant endophytic bacteria are potential candidates to enhance plant-growth promotion in As contamination soils. Characterization of bacterial endophytes with plant growth potential can help us apply them to improve plant yield under stress conditions.