Heavy metal removal by phosphate-solubilizing Enterobacter xiangfangensis isolated from rhizosphere

Industrial activities in the world release large amounts of pollutants including heavy metals. This study was aimed to assess heavy metal removal by phosphate-solubilizing bacteria and evaluation the effects of extracellular factors including phosphatase in removing the metal.
Material & In this experimental study, phosphate-solubilizing bacteria were isolated from Amaranth rhizosphere on Pikovskaya medium, and subsequently identified using molecular methods. Acid phosphatase level was measured by colorimetric method. MIC50 and MBC of nickel, cadmium, chromium, and lead were detected by microplate test. Heavy metal removal through cells or culture supernatant was assessed by atomic absorption spectroscopy. Changes in the level of bacterial cells exposed to heavy metals were evaluated by FTIR method.
The acid phosphatase-producing strain was identified as Enterobacter xiangfangensis. The highest MIC50 (3mM) and MBC (100mM) were obtained for nickel, and the highest metal removal percentage (75.89%) was obtained for the lead. Both nickel and lead were removed by the cells and secreted products. FTIR results showed Ni3(PO4)2 wavelength of 915.058cm-1 in cells treated with 3mM nickel.
Due to the high ability of the isolate in removing nickel and lead by cell surface and secreted materials, this isolate can be used in metal bioremediation. Though the phosphatase enzyme isolated from Enterobacter did not have any considerable effect on lead removal, it was able to remove nickel. Therefore, metal removal can be optimized by enzyme purification.