Potential applications of Pseudomonas sp. (strain CPSB21) to ameliorate Cr(6+) stress and phytoremediation of tannery effluent contaminated agricultural soils

Contamination of agricultural soil with heavy metals has become a serious concern worldwide. In the present study, Cr(6+) resistant plant growth promoting Pseudomonas sp. (strain CPSB21) was isolated from the tannery effluent contaminated agricultural soils and evaluated for the plant growth promoting activities, oxidative stress tolerance, and Cr(6+) bioremediation. Assessment of different plant growth promotion traits, such as phosphate solubilization, indole-3-acetic acid production, siderophores, ammonia and hydrogen cyanide production, revealed that the strain CPSB21 served as an efficient plant growth promoter under laboratory conditions. A pot experiment was performed using sunflower (Helianthus annuus L.) and tomato (Solanum lycopersicum L.) as a test crop. Cr(6+) toxicity reduced plant growth, pigment content, N and P uptake, and Fe accumulation. However, inoculation of strain CPSB21 alleviated the Cr(6+) toxicity and enhanced the plant growth parameters and nutrient uptake. Moreover, Cr toxicity had varied response on oxidative stress tolerance at graded Cr(6+) concentration on both plants. An increase in superoxide dismutase (SOD) and catalase (CAT) activity and reduction in malonialdehyde (MDA) was observed on inoculation of strain CPSB21. Additionally, inoculation of CPSB21 enhanced the uptake of Cr(6+) in sunflower plant, while no substantial enhancement was observed on inoculation in tomato plant.