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The Impact of pH on the Toxicity of Nickel to Burkholderia cepacia PR1301: Implications for Degradation of TrichloroethyleneEPA Grant Number: U915882
Title: The Impact of pH on the Toxicity of Nickel to Burkholderia cepacia PR1301: Implications for Degradation of Trichloroethylene
Investigators: Van Nostrand, Joy D.
Institution: Medical University of South Carolina
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $69,086
RFA: STAR Graduate Fellowships (2001) RFA Text | Recipients Lists
Research Category: Fellowship - Microbiology , Academic Fellowships , Biology/Life Sciences
The overall objective of this research project is to determine if trichloroethylene (TCE) degradation by Burkholderia cepacia PR1301 is inhibited by nickel (Ni) more at high pH than low pH because of a microbially controlled mechanism. The specific objectives of this research project are to determine: (1) if TCE degradation by B. cepacia PR1301 is affected by changes in pH and the presence of Ni; (2) the main mechanism of resistance to Ni in B. cepacia PR1301; and (3) how the mechanism of resistance is mediated by pH. Examination of cell-surface properties, protein expression, Ni sorption, and Ni influx and efflux at various Ni concentrations and at different pH values will be used to examine these objectives.
This project focuses on a site contaminated with chlorinated solvents and heavy metals at the U.S. Department of Energy’s Savannah River facility. Current metal concentrations range from 2 to 5,300 ppm Ni and from less than 1 to 6,100 ppm uranium (U). Ni appears to be providing a greater selection pressure, with more Ni (maximum 100 ppm) found in the porewater (where it would be accessible to the microorganisms) than U (maximum 10 ppm). Four Gram-positive, Ni-resistant organisms (Arthrobacter oxydans, Streptomyces galbus, Streptomyces aureofaciens, and Kitasatispora cystarginea) were isolated and identified using 16S rDNA sequence analysis. Studies with S. aureofaciens suggested that Ni was less toxic at pH 5 than at pH 6 or 7. Because growth of S. aureofaciens is not substantial at pH 5, we chose to study Ni toxicity in B. cepacia PR1301, a constitutive TCE degrader, which grows well at pH 5, 6, and 7. B. cepacia PR1301 grew on higher Ni concentrations at pH 5 (1,000 ppm) than at pH 6 (200 ppm) and 7 (50 ppm). Studies using the MinteqA2 model indicate that there is no speciation difference in our media at pH 5 or 6. At pH 7, Ni begins to precipitate at 1,000 ppm, causing Ni to be less available and potentially less toxic. However, the speciation results and our experimental data do not correlate, because Ni toxicity was greatest at pH 7. Ultimately, our long-term goals are to gain a greater understanding of remediation challenges in mixed-waste environments. By understanding the impact of Ni on the ability of B. cepacia PR1301 to degrade TCE, we can design more effective strategies to clean up mixed-waste sites.