Identification of lead-resistant rhizobacteria of Carthamus tinctorius and their effects on lead absorption of Sunflower

Abstract

Using rhizobacteria as plant growth-promoting agents for improving heavy-metal phytoremediation processes in contaminated soil has attracted a lot of attention mainly because of their eco-friendliness. The aim of this study was the evaluation of lead phytoremediation by Carthamus tinctorius improved with the isolated and molecularly identified lead-resistant rhizobacteria. Rhizobacteria were isolated from C. tinctorius root and was identified using macroscopic and microscopic characteristics, biochemical testing and PCR. Then, the indole acetic acid production and phosphate-solubilizing activity were determined. Finally, the amount of lead in the plant was measured by atomic absorption method. Five strains of Bacillus cereus, Bacillus muralis, Bacillus sp., Pseudomonas fluorescens and Brevibacterium frigoritolerans with the ability of mineral phosphate solubilizing, high levels of indole acetic acid production and resistance to lead were isolated from the rhizosphere of C.tinctorius. The amount of produced indole acetic acid and the level of phosphate solubilizing by the isolates were 7.1-69.54µgml-1 and 91-147.3µgml-1 respectively. Lead assimilation in aerial part of safflower ranged from 925 to 2175ppm. P. fluorescens and B. cereus strains had the highest effect on Lead assimilation with 2175 and 1862ppm respectively. The results showed that different bacterial treatments influenced the rate of lead absorption by C. tinctorius exposed to lead stress. Use of rhizosphere isolates of C. tinctorius can improve phytoremediation capability and lead absorption in lead-contaminated soil.