Optimization of Copper (II) Removal by Response Surface Methodology Using Root Nodule Endophytic Bacteria Isolated from Vigna unguiculata

Abstract

The present study was conducted to investigate copper tolerance and bioremediation potential in endophytic bacteria isolated from Vigna unguiculata root nodules. Total ten endophytes were isolated on yeast mannitol agar and enriched in copper (II) sulfate (CuSO4) up to 500?mg/L. Four endophytes belonging to genera Bacillus and Arthrobacter showed copper tolerance. The isolates were identified as Arthrobacter tumbae MYR1, Bacillus safensis MYR2, Bacillus pumilus MYR3 and Bacillus sp. MYR4 using 16S ribosomal RNA (rRNA) analysis. Response surface methodology was used for copper (II) removal optimization. The model was significant with R2, P and F value of 0.9780, <0.0001, and 34.54, respectively. Results showed that highest copper (II) bioremoval of 82.8?% was obtained at pH 5.0, temperature 32.5??C, and 600?mg/L copper concentration after 168?h of incubation. The isolates were tested for plant growth promotion and all the strains produced indole acetic acid (IAA) and showed 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity. The study concludes that endophytic bacteria possessed greater potential for copper tolerance and bioremediation. ? 2016, Springer International Publishing Switzerland.