Abstract
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−1 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 (arsC) gene. Based on 16S rDNA sequence analysis, these isolates belong to the genera Acinetobacter, Pseudomonas, and Rahnella. All isolates were found As tolerant, of which one isolate, Pseudomonas 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 Pseudomonas sp. QNC1, while nitrogen fixation activity was shown by only Rahnella sp. QNC2 isolate. Acinetobacter sp. QNA1, QNA2, and Rahnella sp. QNC2 exhibited lipase production, while only Pseudomonas sp. QNC1 was able to produce protease. The presence of the arsC 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−1 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 Pseudomonas sp. QNC1 and Rahnella sp. QNC2 induced lower NPR3 gene expression in chickpea roots grown in soil with the final concentration of 100-mg kg−1 sodium arsenate compared with the non-endophyte-treated control. The same results were obtained in Acinetobacter sp. QNA2-treated alfalfa plants grown in the soil plus 50-mg kg−1 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.
Highlights
Plants are constantly affected by abiotic stress excreted by the environment
The phylogenetic analysis illustrated that two strains, namely QNA1 (MN658698) and QNA2 (MN658700) were grouped among species of the genus Acinetobacter and showing the closest 100% similarity with A. calcoaceticus CA16, a bacterium isolated from Canadian soil with bioremediation potential (Ho et al, 2020)
Arsenic is one of the most hazardous environmental pollutants worldwide. It is present in high concentrations in some areas of Kurdistan province and has direct effects on human health
Summary
Plants are constantly affected by abiotic stress excreted by the environment. Heavy metals can reduce plant development and crop productivity when their concentration rises beyond supraoptimal values for plant normal functioning (Tiwari and Lata, 2018). Arsenic (As) is a heavy metal present in various soil and water ecosystem (Chowdhury et al, 1999; Abernathy et al, 2003). A high concentration of arsenic in water, plants, and soils has been reported from the south-eastern part of Kurdistan province, Iran (Mosaferi et al, 2003; Zandsalimi et al, 2011). The concentration of arsenic in these sites ranged from 100–300 mg kg−1 of soil. Heavy contamination of this trace element has adversely affected human health. Uptake and accumulation of arsenic in crops grown in polluted soils lead to poor growth and subsequent yield loss. Arsenic can enter into edible parts of the plant, such as seeds and fruit, making them dangerous for consumers
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