Influencia del cobre sobre la composición taxonómica del picofitoplancton en la bahía de Chañaral

Microorganisms are the most abundant biological entities in the biosphere. Microbial communities are now recognized as critical components of marine food webs and nutrient cycles in the ocean. The autotrophic fractions of such communities are responsible for about half of the total CO2 fixation on earth and the heterotrophic fractions direct a large proportion of total flows of matter and energy. Traditionally, marine picophytoplankton (< 3μm in cell diameter cells) was thought to include only cyanobacteria of the genera Synechococcus and Prochlorococcus. However it has recently been determined that the eukaryotic microbial component of the picophytoplankton, known as picoeukaryotes, are also abundant and important within marine systems. An unexpectedly high diversity of picoeukaryotes has been revealed in marine environments, displaying a dynamic behavior. Both components of the picophytoplankton (bacteria and eukarya) are crucial players in coastal systems. However, basic questions about how such communities are regulated by environmental factors and disturbances are still poorly resolved. The development of new methodologies of study, based on molecular tools, has improved our understanding of these communities and has introduced new ways of understanding how they respond to and regulate the environment in which they live.Many marine coastal systems are subjected to disturbances by human activities. Disturbances related to increases in the concentration of heavy metals such as copper are of particular interest, due to their negative effects on photosynthetic microbial communities. Copper is an interesting trace metal because of its dual role. On one hand, it is needed at trace levels for the correct functioning of the cellular machinery, being part of proteins involved in electron transfer and activation and transport of oxygen, but at higher concentrations copper becomes toxic to the cell. Besides that, both copper-excess and cooper-deficiency differentially affects the different components of the picophytoplankton, in terms of cellular requirements and toxicity. This intrinsically means that ecosystem balance would be altered by copper availability whether at levels that cause toxicity or at levels that relieve metal-limitation for some species. In this context, the relationship between elevated concentrations of metals and changes in picophotosynthetic microbial communities has been poorly studied. Currently, processes of copper mining are responsible by far for the greatest pollution observed due to this metal, creating environmental problems in terrestrial and aquatic ecosystems. However, recent studies indicate that copper pollution could become a more spread problem due to deposition of copper-enrich atmospheric dust.The main objective of this work was to study how communities of picophotosynthetic organisms respond to prolonged exposure to elevated copper levels, with special emphasis on the picoeukaryotic component, through a comparative analysis of coastal areas with different history of exposure to this type of disturbance. We demonstrate that i) copper is the main factor that explain the physico-chemical differences between site, ii) copper does not exert a negative effect over the cellular abundance of picophytoplankton inhabit the area and iii) the community composition of the study area is different from other coastal environments, where low copper levels has been reported. This differences indicates that, in fact, copper levels are pushing to changes in community composition of photosynthetic picoeukaryotes. A sustained and intensively sampling during years are necessary to conclude if the amount of copper, which is deposited daily on the sea, have an impact on microbial communities, which can alter the energy transfer through the food web.