Ensifer adhaerens for heavy metal bioaccumulation, biosorption, and phosphate solubilization under metal stress condition

Abstract

Abstract In this study, a bacterial strain was recovered from the chickpea root surface and its heavy metal tolerance ability, bioaccumulation, biosorption, chromium reduction potential, and phosphate solubilization activity were determined. Bacterial strain (OS3) was molecularly characterized through 16S rRNA partial gene sequencing and confirmed strain sequences belonged to the Ensifer adhaerens , inveterate by the BLASTn and phylogenetic analysis and achived accession number from Genbank # HE681418.1. Strain OS3 was able to tolerate up to 250 µg/ml Cd, 500 µg/ml Cr, 800 µg/ml each of Cu and Zn and 1000 µg/ml Ni. Moreover, strain OS3 was able to bioaccumulate and biosorb varying concentrations of heavy metals and showed maximum accumulation of Ni (95%) and least accumulation of Pb (74%) at a temperature of 34 °C and pH 7. The Langmuir and Freundlich adsorption constants were evaluated from the isotherms with a correlation coefficient ( r 2 > 0.98). The strain reduced 200 µg/ml of Cr (VI) completely after 96 h growth at 35 °C. Apart from bioremedaition ability, bacterial strain OS3 expressed a significant inorganic phosphate (P) solubilizing activity and solubilized inorganic P upto 303 µg/ml with a 2.2 solubilization index. Also, strain OS3 demonstrated plant growth promoting traits even under metal stress and secreted IAA, siderophore, HCN and ammonia under in vitro conditions. This study demonstrated that E. adhaerens survived well, even when exposed to higher concentrations of heavy metals and retained plant growth promoting activities. The biosorption ability, chromium reducing potential and ability to secrete plant growth regulators makes this organisms an interesting choice for metal removal (bioremediation) and enhancing crop production even in metal polluted soils.