Heavy Metal Removal by Phosphate Solubilizing Acinetobacter calcoaceticus Isolated from Rhizosphere

Abstract

Worldwide industrial activities produce large amount of metal wastes. Metals remediation by microbial activities associated with phosphorus metabolism is a promising method. The goals of this study were the removal of some heavy metals by isolated phosphate solubilizing rhizobacterium (PSR) and survey the effect of total secreted materials including extracellular phosphatase on this phenomenon. PSR strain was isolated by Pikovskaya (PVK) medium and identified by 16S rDNA sequencing. Its phosphatase enzyme was assayed by colorimetric method. Metal resistance of the isolate was measured by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The metal removal was detected by atomic absorption spectroscopy. The culture supernatant was analyzed for metal removal by secreted phosphatase enzyme with or without tri-calcium phosphate (TCP), as its substrate. The isolated rhizobacterium was identified as Acinetobacter calcoaceticus that produced acid phosphatase enzyme. The MICs50 were obtained 2.5 mM Pb(II), 2 mM Ni(II), 0.2 mM Cr(II) and E‚1 mM Cd(II); and the MBCs were >100 mM Ni(II), 40 mM Cd(II), 20 mM Pb(II), and 1 mM (Cr(II). The removal of metals by the cells were obtained 29.45% Cr(II), 25.74% Pb(II), 18.85% Cd(II) and 11.43% Ni(II). It was not seen any nickel removal by microbial secreted products in PVK medium without TCP, whereas removal was obtained in PVK complimented by TCP 28.3%; lead removal was almost the same in both media (99%) and was not related to TCP.