title: Adaptation of the chlorophycean Dictyosphaerium chlorelloides to stressful acidic, mine metal-rich waters as result of pre-selective mutations.
abstract: Several species of microalgae, closely related to mesophilic lineages, inhabit the extreme environment (pH 2.5, high levels of metals) of the Spain's Aguas Agrias Stream water (AASW). Consequently, AASW constitutes an interesting natural laboratory for analysis of adaptation by microalgae to extremely stressful conditions. To distinguish between the pre-selective or post-selective origin of adaptation processes allowing the existence of microalgae in AASW, a Luria-Delbrück fluctuation analysis was performed with the chlorophycean Dictyosphaerium chlorelloides isolated from non-acidic waters. In the analysis, AASW was used as selective factor. Preselective, resistant D. chlorelloides cells appeared with a frequency of 1.1 x 10(-6) per cell per generation. AASW-resistant mutants, with a diminished Malthusian fitness, are maintained in non-extreme waters as the result of a balance between new AASW-resistant cells arising by mutation and AASW-resistant mutants eliminated by natural selection (equilibrium at c. 12 AASW-resistants per 10(7) wild-type cells). We propose that the microalgae inhabiting this stressful environment could be the descendents of chance mutants that arrived in the past or are even arriving at the present.
authors.affiliation: Producción Animal (Genética), Facultad de Veterinaria, Universidad Complutense, Madrid, Spain.
authors.forename: Victoria
authors.initials: V
authors.lastname: López-Rodas
authors.forename: Fernando
authors.initials: F
authors.lastname: Marvá
authors.forename: Mónica
authors.initials: M
authors.lastname: Rouco
authors.forename: Eduardo
authors.initials: E
authors.lastname: Costas
authors.forename: Antonio
authors.initials: A
authors.lastname: Flores-Moya
mesh_terms: D000143:Acids / Q000633:toxicity; D000222:Adaptation, Physiological / Q000235:genetics / Q000502:physiology*; D005618:Fresh Water; D008670:Metals / Q000633:toxicity*; D008906:Mining; D009154:Mutation / Q000235:genetics* / Q000502:physiology*; D010839:Phytoplankton / Q000235:genetics / Q000502:physiology*; D013030:Spain; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000633:toxicity*; D014876:Water Pollution / Q000009:adverse effects*
chemical_list: D000143:Acids; D008670:Metals; D014874:Water Pollutants, Chemical