Hexavalent chromium reduction by Pannonibacter phragmitetus BB isolated from soil under chromium-containing slag heap

The objective of this study was to find an indigenous Cr(VI)-reducing bacterium that can effectively be used for Cr(VI) remediation in the contaminated soils. The results showed that one isolate from soil under a chromium-containing slag heap at a steel-alloy factory in China had a strong ability of reducing Cr(VI). It can completely reduce 500 mg L(-1) Cr (VI) within 24 h. Based on 16S rRNA gene sequence and similarity analysis, this isolate was identified as Pannonibacter phragmitetus and assigned as strain BB. Images of scanning electron microscopy (SEM) indicated that the cell surface of P. phragmitetus BB remained intact without cell rupture under 500 mg L(-1) Cr (VI) stress. The transmission electron microscopy (TEM) patterns showed that the Cr(VI) reduction products were both bound to the outer surface of the cells and dispersed in the culture medium, thereby suggesting that the reduction of Cr (VI) occurred extracellularly. Elemental analysis by energy dispersive X-ray (EDX) revealed that Cr was the major element comprising the reduction product. Furthermore, X-ray photoelectron spectroscope (XPS) verified that the Cr(VI) reduction product was Cr(III) compounds.