Intracellular nickel accumulation by Pseudomonas aeruginosa and its chemical nature

Aims: To investigate intracellular localization of nickel and its chemical nature in Pseudomonas aeruginosa. Methods and Results: Transmission electron micrographs of Ni-loaded bacteria exhibited a darkened electron opaque zone throughout the cell periphery. Energy dispersive X-ray analysis confirmed the deposition of metallic nickel. Cell fractionation revealed that 88% of the accumulated nickel was restricted to the periplasm and membrane. X-ray diffraction patterns ascertained the chemical nature: of cellular Ni as phosphide (Ni5P4, NiP2 and Ni12P5) and carbide (Ni3C) crystals. Conclusions: Pseudomonas aeruginosa accumulated nickel as its phosphide and carbide crystal mostly in the cell envelope region, indicating the predominant role of phosphoryl and carboxyl/carbonyl groups of cell wall/membrane components in cation sequestration. Significance and Impact of the Study: The data contribute significantly to a better understanding of bacteria-metal interaction and will be useful in developing biotechnological strategies for toxic metal bioremediation.