Role of soil associated Exiguobacterium in reducing arsenic toxicity and promoting plant growth in Vigna radiata

• The soil bacterium Exiguobacterium (As-9) is highly resistant to arsenic.
• As-9 removed 90% As(III) and 99% As(V) during growth.
• The bacteria showed plant growth promoting ability.
• It enhanced the growth of Vigna radiata in presence of arsenic.
• It helped in reducing oxidative stress in plants.

The present work describes the effects of inoculating metal resistant and plant growth promoting bacteria (PGPB) on the growth of Vigna radiata under arsenic (As) stress. The Exiguobacterium sp. strain, As-9 was isolated from arsenic contaminated soil, which showed resistance to exceptionally high concentrations of As(V) and As(III). Assessment of plant growth promoting parameters revealed the ability of the strain for the solubilization of phosphate, production of indole-3-acetic acid (IAA) and exopolysaccharide (EPS). Soil inoculated with this arsenic resistant PGPB in the presence of high concentrations of As(V) and As(III) was used for the germination of seeds of V. radiata under controlled conditions. The in vitro experiments proved that Exiguobacterium significantly (p < 0.05) increased the shoot and root biomass of V. radiata in the presence of As(V) and As(III) together with increase in the plant height, survival index and chlorophyll content after 15 days of inoculation. It also protected the plants from the detrimental effects of arsenic by reducing its uptake and translocation by colonizing the root surface. In addition, assay of antioxidant enzymes and lipid peroxidation test revealed significant (p < 0.01) reduction in arsenic-induced oxidative stress in V. radiata in the presence of bacteria. Owing to its wide action spectrum, the arsenic resistant PGPB could provide a new insight into the remediation of arsenic contaminated soil and serve as an effective growth promoting bioinoculant for plants in metal stressed soil.

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