Effects of acetaminophen, diclofenac and ibuprofen exposure on growth, viability, photosynthetic pigment production and gene expression in Synechococcus elongatus for the assessment of its bioremediation potential

Abstract

The extensive use of pharmaceuticals has led to the accumulation of emergent pollutants with potential toxicity to aquatic organisms in water bodies around the world. Non-steroidal anti-inflammatory drugs (NSAIDs), such as acetaminophen (ACP), diclofenac (DCF) and ibuprofen (IBU) are amongst the most prevalent pharmaceuticals found in surface water and wastewater at levels up to 10,000 ng/L. In the present work, a Mexican strain of Synechococcus elongatus was selected to characterize the effects of ACP, DCF and IBU on the cyanobacteria growth rate, viability, photosynthetic pigment content (chlorophyll, carotenoids and phycobiliproteins), and expression level of three stress-related genes (aphC, htpG, and mutM). S. elongatus was able to tolerate continued exposure to ACP and DCF with 2.43% and 12.40% inhibition to its growth rate under ACP and DCF, respectively; exposure to IBU led to complete growth inhibition. Cultures treated with ACP and DCF did not show significant change in chlorophyll and phycobiliprotein content but did show a statistically significant increase in carotenoids (13.90% under ACP, p < 0.05) after 10 days of culture. IBU treated cultures presented total loss of photosynthetic pigments except for chlorophyll, with a 70% decrease compared to control, showing a similar state to chlorosis in cyanobacteria. RNA levels showed an increase in aphC expression under all treatments but was only statistically significant under DCF (6.29-fold increase, p < 0.05); expression of htpG and mutM was downregulated without statistical significance under all treatments. These results suggest an increase in the antioxidant defense response (aphC) against reactive oxygen species under exposure to NSAIDs. Finally, S. elongatus was not able to decrease the level of NSAIDs present in the culture. This research work presents a deeper understanding of the effect of contaminant NSAIDs over cyanobacteria and suggests a potential industrial application of S: elongatus culture under pharmaceutical-contaminated wastewater.