Isolation of Pb(II)-reducing bacteria and demonstration of biological Pb(II) reduction to metallic Pb

Pb(II) contamination imposes serious threats to human health and the environment. Biological reduction of Pb(II) to metallic Pb is an attractive method for the remediation of Pb(II)-contaminated water and sediments. In this study, Pb(II)-reducing microorganisms were isolated by the dilution-to-extinction (DTE) and streak-plate methods. As a result, Delftia acidovorans, Azonexus caeni, and Comamonas testosteroni were successfully isolated. At a high lead concentration (10 mg-Pb(II)/L), each of the isolated D. acidovorans strain Pb11 and A. caeni strain Pb2 cultures showed successful utilization of Pb(II), resulting in a 5.15- and 8.14-fold growth in 3 days, respectively. Pb(II) reduction to metallic Pb by D. acidovorans strain Pb11 and A. caeni strain Pb2 was confirmed using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) was coupled with X-ray photoelectron spectroscopy (XPS). This strategic analysis was necessary to confirm the formation of metallic Pb separately from lead phosphate precipitates which are inevitable in the biological Pb(II) removal experiments. Among the 3 isolated microbes, C. testosteroni strain Pb3 did not leave immobile and detectable Pb solids in SEM-EDS analyses. D. acidovorans and A. caeni are recommended for engineered remediation of Pb(II)-contaminated wastewater and sediments.