Chromium uptake, retention and reduction in photosynthetic Euglena gracilis
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ORIGINAL PAPER
Chromium uptake, retention and reduction in photosynthetic Euglena gracilis J. D. Garcı´a-Garcı´a Æ J. S. Rodrı´guez-Zavala Æ R. Jasso-Cha´vez Æ D. Mendoza-Cozatl Æ Rafael Moreno-Sa´nchez
Received: 14 November 2008 / Revised: 14 January 2009 / Accepted: 25 February 2009 / Published online: 17 March 2009 Ó Springer-Verlag 2009
Abstract Photosynthetic Euglena gracilis grown with different K2CrO4 concentrations was analyzed for its ability to take up, retain and reduce Cr(VI). For comparison, cells were also exposed to CrCl3. Cellular Cr(VI) uptake at pH 7.2 showed a hyperbolic saturation pattern with Km of 1.1 mM, Vm of 16 nmol (h 9 107 cells)-1, and Ki sulfate of 0.4 mM. Kinetic parameters for sulfate uptake were similar, Km = 0.83 mM, Vm = 15.9 nmol (h 9 107cells)-1 and Ki chromate = 0.3 mM. The capacity to accumulate chromium depended on the ionic species, external concentration and pH of the incubation medium. Cr(VI) or Cr(III) accumulation was negligible in the acidic (pH 3.5) culture medium, in which Cr(VI) was abiotically reduced to Cr(III). At pH 7.2 Cr(VI) was fully stable and high accumulation ([170 nmol/1 9 107 cells at 1 mM K2CrO4) was achieved; surprisingly, Cr(III) accumulation was also significant ([35 nmol/1 9 107 cells at 1 mM CrCl3). Cr(VI) was reduced by cells at pH 7.2, suggesting the presence of an external reductive activity. Cr(VI) induced an increased cysteine and glutathione content, but not in phytochelatins suggesting that chromium accumulation was mediated by monothiol compounds.
Communicated by Erko Stackebrandt. J. D. Garcı´a-Garcı´a J. S. Rodrı´guez-Zavala R. Jasso-Cha´vez D. Mendoza-Cozatl R. Moreno-Sa´nchez (&) Departamento de Bioquı´mica, Instituto Nacional de Cardiologı´a, Juan Badiano # 1, Seccio´n XVI, Tlalpan, 14080 Mexico D.F., Mexico e-mail: [email protected]; [email protected]
Keywords Chromium uptake Sulfate uptake Chromium accumulation Chromium reduction Cysteine Glutathione
Introduction Heavy-metal environmental pollution mainly comes from industrial activities (tannery, chemical, electrical, metal finishing, paint and cement; Palmer and Wittbrodt 1991); however, household and personal activities may also contribute. Household pollution originates from the use of laundry products such as detergents and bleachers (Jenkins and Russell 1994). The most abundant element in these products is As, followed by Zn and Cr. Smoking may be another source of heavy-metal pollution. Cigarettes contain Cd, Cr, Ni and Pb, from which 0.3 to 10%, are released in the smoke and inhaled and incorporated into the human organism (Rodrı´guez-Zavala et al. 2007). Cr(III) and Cr(VI) are the most stable and abundant chromium species used for industrial activities and, hence, they represent the main chromium environmental pollutants (Barnhart 1997). Some heavy metals and metalloids, such as Cr(VI), Ni2?, Co2?, Cd2?, As(III), and Pb2?, are carcinogenic for humans and other mammals (Norseth 1988; Hayes 1997). However, a wide variety of plants, fu
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