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VICTORIA LÓPEZ-RODAS Y COLS. AN. R. ACAD. NAC. FARM.

This fact seems to be the pattern followed by microalgae in extreme
geothermal waters of Eolias islands, Italia and Argentina (38, 40).

The most abundant species in the crude oil area was the
cosmopolite mesophile Chlorophyta Scenedesmus obtusus. This
species is able to grow rapidly under the extreme crude oil
contamination of Arroyo Minero as well as under a Fluka Analytical
Petroleum Special Standard. However, crude oil of Arroyo Minero
and Petroleum Special Standard caused inhibition of more than
50% of effective quantum yield of photosystem II of Scenedesmus
intermedius, with died afterwards. This species closely related with
Scenedesmus was isolated from a pristine lagoon in Doñana National
Park, which never was exposed to petroleum prior to the experiment.
This fact suggest the four species proliferating in the spill area of
Arroyo Minero are the result of some kind of genetic evolutionary
change occurs in the past, which allows the adaptation of
phytoplankton to extreme crude oil contamination.

In extreme environments characterized by values of envi-
ronmental contaminants exceeding the physiological limits of
organisms, survival of microbes depends exclusively of selection on
pre-existing genetic variability that occurs spontaneously by rare
spontaneous mutation [i.e. mutations occur exclusively by chance
and independently of the selective agent; reviewed by Sniegowski
(41)]. However, some microbiologist debates this neo-Darwinian
theory suggesting an alternative explanation called adaptationist
process [reviewed by Creager (42)]. In some cases, adaptive mutation
mutations occur in bacteria as a direct and specific response to
the selective agent (43, 44). However a lot of works on adaptation
of algae to antibiotics, toxic substances and extreme environments
have find that adaptation depends exclusively of selection on rare
spontaneous mutants that occurs prior to exposure at selective agent
(45-52).

Finally, although several studies recorded phytoplankton flora
from N Argentina (i.e. 23-26, 53), the knowledge of the flora of
phytoplankters of Patagonia Argentina is very scant. We identify
two species from crude oil spill of Arroyo Minero (Symploca dubia
and Chlamydomonas dinobryonis) that are new records for flora
of Argentina. Other species could be a new species (Scenedesmus

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