Browsing by Author "P. Sar"

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Intracellular nickel accumulation by Pseudomonas aeruginosa and its chemical nature
(Blackwell Publishing Ltd., 2001) P. Sar; S.K. Kazy; S.P. Singh
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.
Metal adsorption and desorption by lyophilized Pseudomonas aeruginosa
(1999) P. Sar; S.K. Kazy; R.K. Asthana; S.P. Singh
Biosorption of nickel (Ni2+) and copper (Cu2+) by lyophilized Pseudomonas aeruginosa cells was investigated based on Freundlich isotherm. Bacterial biomass showed significant sorption of both Ni (265 mg g-1) or Cu (137.6 mg g-1), and was also superior over the cation exchanger, IRA 400 (98 mg Ni g-1 or 26.6 mg Cu g-1). Metal binding by the test organism was a fast saturating, pH-dependent process. The optimum pH for Cu adsorption was 7.0 and for Ni 8.0. X-ray diffraction studies revealed that both cations were deposited on the cell predominantly as phosphide crystals. The participation of carboxyl, carbonyl, and phosphoryl groups along with H-bonding in metal sorption was evident in IR spectra. Biomass pretreatment by agents like NaOH, NH4OH or toluene enhanced the metal loading capacity, whereas, oven heating (80°C), autoclaving (120°C, 15 lb (in.2)-1), acid, detergent and acetone treatments were inhibitory. In bimetallic combination, Na, K or Ca increased sorption of Ni as well as Cu in contrast to Cd or Pb. Mineral acids (HCl, H2SO4 and HNO3) and NTA could recover more than 75% (on average) Ni or Cu adsorbed on the biomass. Calcium carbonate (10 mM) was efficient in Ni desorption (71%) compared to Cu (57%). Noticeably sodium carbonate remained specific for Cu remobilization (88%) than Ni (21%). The data are in favour of deployment of the test biomass as an efficient metal removal/recovery system.