Exploring the survival tactics and plant growth promising traits of root-associated bacterial strains under Cd and Pb stress: A modelling based approach

The study represents a microbial method for reducing heavy metal stress in terrestrial environment. Two rhizobacterial strains Pantoea agglomerance (PC1) and Pseudomonas aeruginosa (SA) having the ability to tolerate Cd²⁺ and Pb²⁺ ions stress, were employed in this study. The growth promotion and survival tactics of the strains under metal stress were explored through kinetic growth model using logistic equation, Luedeking-Piret model and Box Behnken design. Study also involves the interaction of strains with Zea mays L. under Cd²⁺ and Pb²⁺ ions stress. Results revealed that both strains have the potential to tolerate 500 mg L⁻¹ of Cd²⁺ and Pb²⁺, ions and maintained the plant growth promoting traits. The Luedeking-Piret model estimated the maximum value of IAA on biomass growth (Y_P/X) 5.377 μg g⁻¹ and 10.3 μg g⁻¹ under Cd²⁺ ions, while 7.742 μg g⁻¹ and 18.071 μg g⁻¹ under Pb²⁺ ions stress for strains SA and PC1, respectively. Further, phosphate solubilization activity was optimized with the help of response surface methodology using Box Behnken Design. The optimum solubilization by strain PC1 and SA was achieved at 100 and 150 mg L⁻¹ of Cd²⁺, and 150 and 200 mg L⁻¹ of Pb²⁺ ion concentration at the pH range 6.75 and 7.5 respectively. The interactive study with Zea mays L. showed significant increase in seed germination in the presence of Cd²⁺ and Pb²⁺ ions thereby proving them as potent plant growth promoters and metal stress reducing biological agents. Hence, the findings of the study suggest that rhizobacterial strains could be a sustainable tool for restoration of metal contaminated sites.