Multi-biomarker response of cyanobacteria Synechocystis salina and Microcystis aeruginosa to diclofenac.

The cyanobacterial response to pharmaceuticals is less frequently investigated compared to green algae. Pharmaceuticals can influence not only the growth rate of cyanobacteria culture, but can also cause changes at the cellular level. The effect of diclofenac (DCF) as one of the for cyanobacteria has been rarely tested, and DCF has never been applied with cellular biomarkers. The aim of this work was to test the response of two unicellular cyanobacteria (Synechocystis salina and Microcystis aeruginosa) toward DCF (100 mg L-1) under photoautotrophic growth conditions. Such endpoints were analyzed as cells number, DCF uptake, the change in concentrations of photosynthetic pigments, the production of toxins, and chlorophyll a in vivo fluorescence. It was noted that during a 96 h exposure, cell proliferation was not impacted. Nevertheless, a biochemical response was observed. The increased production of microcystin was noted for M. aeruginosa. Due to the negligible absorption of DCF into cells, it is possible that the biochemical changes are induced by an external signal. The application of non-standard biomarkers demonstrates the effect of DCF on microorganism metabolism without a corresponding effect on biomass. The high resistance of cyanobacteria to DCF and the stimulating effect of DCF on the secretion of toxins raise concerns for environment biodiversity.

Biochemical and physiological aspects of chlorophyll breakdown / Biochemiczne i fizjologiczne aspekty rozkladu barwników chlorofilowych.

During leaf senescence and fruit ripening chlorophyll is broken down into nonfluorescent catabolites (NCCs). The chlorophyll degradation pathway includes a series of biochemical transformations ocurring sequentially in chloroplasts, cytosol and vacuoles. The path begins with enzymatic reduction of chlorophyll b to chlorophyll a. Next, the specific dechelatase and esterase remove the magnesium atom and the phytol chain resulting in the formation of pheophorbide a. In the next step, the porphyrin macroring is opened by pheophorbide a oxygenase and red catabolite reductase. The product of this transformation is an early fluorescent catabolite (pFCC), which after hydroxylation and species-specific modifications is imported into the vacuole. In acidic medium of the vacuole pFCC undergo isomerization to their respective colorless NCCs, which are final chlorophyll degradation products in higher plants. There are still no answers to a number of questions about the fate and significance of millions tons of chlorophyll catabolites released annually in the aquatic environment as a result of cellular senescence and death of phytoplankton. A few reports indicate that algae and cyanobacteria may metabolize their photosynthetic pigments in a similar way as higher plants do, however, the course of chlorophyll breakdown in these organisms has not been yet elucidated.