Interactions between the antimicrobial agent triclosan and the bloom-forming cyanobacteria Microcystis aeruginosa

• Triclosan inhibit the growth and photosynthesis of M. aeruginosa at environmental relevant level.
• TEM imaging showed destruction of M. aeruginosa cell ultrastructure during triclosan exposure.
• Triclosan can be biotransformed by M. aeruginosa with methylation as a major pathway.
• Presence of M. aeruginosa enhanced the photodegradation of triclosan.

Cyanobacteria can co-exist in eutrophic waters with chemicals or other substances derived from personal care products discharged in wastewater. In this work, we investigate the interactions between the antimicrobial agent triclosan (TCS) and the bloom-forming cyanobacteria Microcystis aeruginosa. M. aeruginosa was very sensitive to TCS with the 96 h lowest observed effect concentration of 1.0 and 10 μg/L for inhibition of growth and photosynthetic activity, respectively. Exposure to TCS at environmentally relevant levels (0.1–2.0 μg/L) also affected the activities of superoxide dismutase (SOD) and the generation of reduced glutathione (GSH), while microcystin production was not affected. Transmission electron microscope (TEM) examination showed the destruction of M. aeruginosa cell ultrastructure during TCS exposure. TCS however, can be biotransformed by M. aeruginosa with methylation as a major biotransformation pathway. Furthermore, the presence of M. aeruginosa in solution promoted the photodegradation of TCS. Overall, our results demonstrate that M. aeruginosa plays an important role in the dissipation of TCS in aquatic environments but high residual TCS can exert toxic effects on M. aeruginosa.