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ABSTRACT Some species of cyanobacteria have the ability to grow under stress conditions that would kill many other bacteria. Solutions of 0.25 mM Cu2+ were inoculated with the cyanobacteria Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803 with the idea that these cyanobacteria may develop certain defense mechanisms allowing their survival in such stressed environments. Transmission electron microscopy showed that Synechocystis sp. grown in 0.25 mM copper(II) developed a filamentous sheath around the cell wall, which could be responsible for binding copper ions on the cell surface. The presence of copper adsorbed by Synechocystis sp. was corroborated using environmental scanning electron microscopy equipped with an x-ray energy-dispersive spectrometer. Synechococcus has the ability to grow in mass quantity under ideal conditions, providing usable biomass at a minimal effort. Using lyophilized biomass grown under normal conditions, Synechococcus was tested for its potential to bind copper(II), lead(II), and nickel(II) ions from solution. Batch experiments were performed to determine the optimum binding pH, time dependency, and metal binding capacities for copper(II), lead(II), and nickel(II), along with desorption of the metal bound. The biomass studied showed a high affinity for all metal ions as the pH increased from two to six with optimum binding occurring at pH 5. Time dependency studies showed that this cyanobacterium had rapid binding to all three metals. Capacity experiments showed that this cyanobacterium bound 11.3 mg of copper(II) per gram of biomass, 30.4 mg of lead(II) per gram of biomass, and 3.2 mg of nickel(II) per gram of biomass. More than 98% of the copper(II), lead(II) and nickel(II) adsorbed by the biomass was recovered when treated with 0.1M HCl. Cyanobacterial biomass can eventually be used as the source for a novel approach in using biosystems to remediate contaminants from solution.
KEYWORDS: Synechococcus, Synechocystis, cyanobacteria, heavy metal binding, bioremediation
This paper is from the Proceedings of the HSRC/WERC Joint Conference on the Environment, May 1996, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.
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