Department of Environmental Chemistry, IDAEA-CSIC, Jordi Girona 18-26, Barcelona,
Catalunya, Spain
E-mail contact: mcarmen.fernandez-pinos@idaea.csic.es
Semivolatile persistent organic pollutants are introduced into remote oceanic regions by atmospheric transport and deposition, with the subsequent effects on aquatic organisms.
Previous studies proved that organic pollutants present in seawater affect abundance, growth rate and cell viability of phytoplankton, suggesting that mixtures of contaminants could influence ecosystem functions like oceanic CO
2
fixation or productivity. The cyanobacterium
Prochlorococcus numerically dominates the photosynthetic community in the tropical and subtropical regions of the world’s oceans, so its contribution to primary production is significant.
Being the smallest known photosynthetic organism, i ts tiny size and spherical shape provide a high surface to volume ratio, making it very prone to acumulate organic chemicals and particularly sensitive to pollutants. .
As a part of a large project to evaluate the effects of organic pollutants on the marine carbon cycle, the potential impact of organic pollutants on photosynthetic function of phytoplankton was performed during the Malaspina circumnavigation cruise (December 2010 - July 2011). A total of 16 experiments were performed in the Indian, Pacific and Atlantic Oceans. Natural communities from the deep chlorophyll maximum (DCM) depth were challenged with three different organic pollutant mixtures (PAHs; HCB+HCHs; and a complex mixture form concentrated seawater) and incubated at 4 exposure times. To monitor the effects of the treatments on the photosynthetic function, mRNA abundances of rbc L (RuBisCO), psb A (D1 protein) and rnp B (reference gene) for each of the two major Prochlorococcus clades (high light and low light), were assessed by qRT-PCR for each experiment.
Preliminary results show that the complex mixture of pollutants produced a decrease of rbc L expression after 6h and 24h of exposure, particularly for the high light clade, whereas the other two mixtures tested did not induced any effect. This confirms an effect of cocktails of pollutants at environmentally relevant concentrations that it not observed when we tested single families of them at similar concentrations. The downregulation was only found in rbc L while psb A remained unaltered, which suggests a specific effect on the CO
2 fixation but no on the complete photosynthetic apparatus. The decrease of rbc L expression together with effects at cellular level could exert a perturbation on the marine carbon cycle.
Key words: organic pollutants, Prochlorococcus, gene expression, marine carbon cycle.