The role of multi-heavy metal tolerant bacteria isolated from the rhizosphere of Eichhornia crassipes in the phytoremediation of Cu and Pb under laboratory conditions was investigated. The heavy metal tolerant rhizosphere bacteria were identified as Bacillus cereus, Paenibacillus alvei, Aeromonas caviae, Paenibacillus taiwanensis, and Achromobacter spanius. Results showed a significant variation in wet weight, Heterotrophic Plate Count (HPC) of the rhizosphere, HPC of water, removal and uptake of Cu and Pb by E. crassipes, either alone or in association with the rhizosphere bacteria. The removal of Cu by E. crassipes in different experimental conditions showed that OTC (Oxytetracycline) untreated E. crassipes with rhizosphere bacteria has maximum removal with 95%, followed by E. crassipes alone with 84%. The OTC treated E. crassipes with rhizosphere bacteria could remove 81% of Cu. The maximum Pb removal efficiency of 93.4% was shown by OTC untreated E. crassipes with rhizosphere bacteria, followed by E. crassipes alone with 86.8%. The OTC treated E. crassipes with rhizosphere bacteria showed the least removal efficiency with 82.32%. The translocation factor (TF) values for Cu and Pb were lower than 1 indicated that the absorption was mainly accomplished in the roots of E. crassipes. The order of accumulation of Cu and Pb in E. crassipes was noted as root > leaf > petiole.
Keywords: E. crassipes; Rhizosphere; heavy metal tolerance; phytoremediation; tropical wetland.
The present work reveals the role of rhizosphere bacteria of E. crassipes in removing both Cu and Pb from an aqueous solution. Comparatively, the plants inoculated with rhizosphere bacteria have shown higher removal efficiency than both normal and OTC treated plants under the experimental conditions.