Brevundimonas diminuta MYS6 associated Helianthus annuus L. for enhanced copper phytoremediation

Natural occurring metal-tolerant microbial population have replaced conventional expensive metal remediation approach since the last few years. The present study focuses on investigating the potential of a copper-tolerant plant growth promoting rhizobacterial strain Brevundimonas diminuta MYS6 for Cu bioremediation, plant growth promotion and Cu uptake in Helianthus annuus L. Box-Behnken Design of response surface methodology optimized the influencing parameters such as pH, temperature and Cu concentration. At optimized conditions of pH (5), temperature (32.5 °C) and Cu concentration (250 mg/L), the rhizobacteria followed a sigmoid growth curve pattern with maximum Cu removal of 94.8% in the stationary phase of growth. Cu exposed Brevundimonas diminuta MYS6 produced increased EPS (18.6%), indicating their role in internal defence against Cu stress. The FTIR analysis suggested the role of carboxylic acids, alcohols and aliphatic amine groups in Cu bioremoval. Furthermore, the results of pot experiments conducted with Helianthus annuus L. var. CO4 and Brevundimonas diminuta MYS6 showed enhanced plant growth and Cu uptake. The rhizobacteria increased root and shoot length, fresh and dry plant biomass and leaf chlorophyll by 1.5, 1.7, 9.9, 15.8 and 2.1 fold. The plant biomass mediate enhanced Cu uptake in roots and shoots was found to be 2.98 and 4.1 folds higher when compared to non-inoculated treatment. Henceforth the results of the study evidence the rhizobacterial strain Brevundimonas diminuta MYS6 as an efficient bio-inoculant for copper remediation.