Plant-Microbe Interactions for Phytoremediation of Multi-Metal Contaminated Soil With Two Brassica Cultivars and Bacterial Strains

Abstract

Contamination of the soil and environment with the toxic heavy metals and their metabolites is a serious environmental problem. In terms of contaminating agricultural soil and water, heavy metals lead the list of environmental pollutants. Our hypothesis is that bacteria that can mobilize biologically inaccessible heavy-metal fractions, cause alterations in root exudation, and stimulation of plant development, as well as are responsible for the increased accumulation of heavy metals by plants. Heavy metals may be extensively mobilized by rhizosphere bacteria and root exudates, increasing their bioavailability. The study focused on integration of bioaugmentation and phytoextraction for Cu, Cu, Cd and Pb (multi-metal) contaminated soil remediation in rhizosphere of Brassica juncea and NARC sarsoon in combination with Bacillus tequilensis, Serratia marcescens and Bacillus safensis strains with the focus on root exudates production and role in aiding the process. The results revealed that the (T12) with the Brassica juncea cultivar and consortia of strains demonstrated the highest extraction for Pb (80.79%), Cu (69.00%) and Cd (63.96%) metal extraction as compared to control T2 which extracted metal Pb (17.51%), Cu (20.98%) and Cd (17.69%). The best treatment for NARC sarsoon variety was T13 with bacterial consortium and extracted metal Pb (46.60%), Cu (46.94%) and Cd (37.96%) as compared to control T2 which extracted metal Pb (8.66%), Cu (19.52%) and Cd (11.48%). Variations in biochemical stress indicators showed significantly lower levels of MDA and H2O2, as well as higher levels of chlorophyll a (0.591 mg/g FW), Chl b (0.363 mg/g FW), total chlorophyll (0.404 mg/g FW), and carotenoids (151 mg/g FW) for T12 and comparable level of chlorophyll a (0.353 mg/g FW), Chl b (0.226 mg/g FW), total chlorophyll (0.580 mg/g FW), and carotenoids (114.8 mg/g FW) for T13. Integrated bio-augmentation and phytoextraction approach has a great potential for remediation of heavy metals rather than a single biological method. Key Words: Phytoremediation, Bioaugmentation, Brassica, Cadmium, Lead, Copper, Root Exudates