Enhanced Tolerance to Mercury in a Streptomycin-Resistant Strain of Euglena gracilis |
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Authors: | Silvia Devars Jos�� Salud Rodr��guez-Zavala Rafael Moreno-S��nchez |
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Affiliation: | 1. Departamento de Bioqu??mica, Instituto Nacional de Cardiolog??a, Juan Badiano No. 1, Seccion XVI, Tlalpan, Mexico, Distrito Federal, 14080, Mexico
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Abstract: | Toxicity of Hg2+ was determined in two strains of Euglena gracilis var. bacillaris: the wild-type (B) and a streptomycin-resistant strain (Smr). Cells were cultured under 12-h dark/12-h light regime or under continuous darkness. In the dark/light cultures, cellular growth was severely diminished in the B strain by Hg2+, whereas only a slight decrease was attained in the Smr strain; Hg2+ also affected the photosynthetic and respiratory activities of the B strain, but not those of Smr strain. Under continuous darkness, cellular growth of both strains was lower than under dark/light cycles, but it was inhibited by Hg2+ to a much lesser extent. Cell culture by 5 days under continuous dark or by 8 days of dark/light cycles resulted in a higher intracellular content of mercury in B strain than in Smr strain. In contrast, in both culture conditions, the fraction of mercury removed from medium by B strain was lower than that attained by Smr strain, whereas the ability to bio-transform (reduce) Hg2+ was two times higher in the mutant strain. The results suggested that Smr strain cells acquired an ability to remove Hg2+ from the medium, which was not associated to accumulation and which conferred protection against mercury. |
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