Tolerance and Biosorption of Heavy Metals by Cupriavidus metallidurans strain XXKD-1 Isolated from a Subsurface Laneway in the Qixiashan Pb-Zn Sulfide Minery in Eastern China

Abstract

The heavy metal-resistant bacterial strain Cupriavidus metallidurans XXKD-1, was isolated from a 475 m subsurface laneway in the Qixiashan Pb-Zn mine, near Nanjing City in eastern China. The phylogenetic analysis based on the 16S rRNA gene sequence shows that the microorgamism has 99% similarity to C. metallidurans CH34. Minimal inhibitory concentrations (MICs) of metals for the bacterium were determined. The bacterial strain XXKD-1 exhibited high MIC values for various heavy metals and a large spectrum of antibiotic resistance. The order of toxicity of the metals to the bacterium was Cd2+ (1 mM) > Co2+ (2 mM) > Cr3+ (2.5 mM) > Ni2+ (3 mM) > Cu2+ (3.5 mM) > Mn2+ (6 mM) > Zn2+ (10 mM) in Tris minimal broth media. Metal bioaccumulation was determined during the course of growth. C. metallidurans strain XXKD-1 is a very efficient biosorbent. It can remove 74% Mn, 53% Cd, 52% Co, 48% Zn and 4% Cr in the cell walls and 4% Mn, 12% Cd, 11% Co, 9% Zn and 50% Cr in intracellular spaces during the active growth cycle (using initial heavy metal concentrations of 0.5 mM). However, it did not efficiently accumulate Cu and Ni, removing only 12% and 10% with total metal biosorption capacities of 3.8 mg/L (0.06 mM) and 3.1 mg/L (0.053 mM), respectively. Because C. metallidurans cells could grow in the presence of elevated concentrations of metals and present relatively high heavy metal biosorption capacities in aerobic conditions, this bacterium may have potential applications for the in-situ bioremediation of heavy metal-contaminated aqueous (or soil) systems in mine ecosystems.