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Short-term adaptation of microalgae in highly stressful environments: an experimental model analysing the resistance of Scenedesmus intermedius (Chlorophyceae) to the heavy metals mixture from the Aznalcóllar mine spill

Published online by Cambridge University Press:  18 December 2002

R. BAOS
Affiliation:
Estación Biológica de Doñana, Consejo Superior de Investigaciones Científicas, Avd. de María Luisa s/n, Pabellón del Perú, 41013, Seville, Spain
L. GARCÍA-VILLADA
Affiliation:
Genética, Facultad de Veterinaria, Universidad Complutense, 28040, Madrid, Spain
M. AGRELO
Affiliation:
Departamento NBQ, F.N. La Marañosa, Ministerio de Defensa, PO Box 1105, Madrid, Spain
V. LÓPEZ-RODAS
Affiliation:
Genética, Facultad de Veterinaria, Universidad Complutense, 28040, Madrid, Spain
F. HIRALDO
Affiliation:
Estación Biológica de Doñana, Consejo Superior de Investigaciones Científicas, Avd. de María Luisa s/n, Pabellón del Perú, 41013, Seville, Spain
E. COSTAS
Affiliation:
Genética, Facultad de Veterinaria, Universidad Complutense, 28040, Madrid, Spain
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Abstract

The toxic spill of acid wastes rich in heavy metals/metalloids (AWHM) from the Aznalcóllar mine in April 1998, threatening the Doñana National Park, is considered to be the worst environmental disaster related to acute pollution in Spanish history. The aim of this work was to study the adaptation of microalgae (which play an important role as primary producers) from AWHM sensitivity to AWHM resistance by using the alga Scenedesmus intermedius as an experimental model. The Malthusian parameter (m) and the carrying capacity (K) were reduced by mud and soil samples collected from the affected area. A dose–effect analysis showed that fitness progressively diminished with increasing sample concentration. A fluctuation analysis demonstrated that AWHM-resistant cells arose by rare spontaneous mutations that occurred randomly prior to the incorporation of the AWHM. The rate of spontaneous mutation from AWHM sensitivity to AWHM resistance was 2.12×10−5 mutants per cell division. A competition experiment between wild-type AWHM-sensitive cells and AWHM-resistant mutants showed that in small populations the AWHM-resistant mutants are driven to extinction in the absence of selection for AWHM resistance. The resistant phenotypes are maintained in the absence of AWHM as the result of a balance between spontaneous mutation and natural selection, so that about 43 AWHM-resistant mutants per million cells are present in the absence of AWHM. Our experimental model suggests that mutation is essential for adaptation of microalgal populations to environmental changes. Rare spontaneous pre-adaptive mutation is enough to ensure the survival of microalgal populations in contaminated environments when the population size is large enough.

Type
Research Article
Copyright
© 2002 British Phycological Society

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