Responses of cyanobacterium Microcystis aeruginosa under single and repeated ofloxacin exposure

Antibiotics are omnipresent and pseudo-persistent in the environment. Yet, their potential ecological risks under repeated exposure, which is more environmentally relevant, are understudied. Therefore, this study used ofloxacin (OFL) as the probe chemical to investigate the toxic effects of different exposure scenarios-single dose of high concentration (4.0 mu g/L) and multiple additions of low concentrations-towards the cyanobacterium Microcystis aeruginosa. Flow cytometry was employed to measure a collection of biomarkers, including endpoints related with biomass, single cell properties and physiological status. Results showed that the single dose of the highest OFL level inhibited cellular growth, chl-a content and cell size of M. aeruginosa. In contrast, OFL induced stronger chl-a autofluorescence and higher doses tended to have more remarkable effects. Repeated low OFL doses can more significantly increase the metabolic activity of M. aeruginosa than a single high dose. Viability and cytoplasmic membrane were not affected by OFL exposure. Oxidative stress was observed for the different exposure scenarios, with fluctuating responses. This study demonstrated the different physiological responses of M. aeruginosa under different OFL exposure scenarios, providing novel insights into the toxicity of antibiotics under repeated exposure.

Automated summary

This study investigated the toxic effects of the antibiotic ofloxacin (OFL) on the cyanobacterium Microcystis aeruginosa under different exposure scenarios, including a single high dose and multiple additions of low concentrations. The results showed that the highest OFL level inhibited cellular growth, chl-a content, and cell size of M. aeruginosa, while higher doses induced stronger chl-a autofluorescence. Repeated low OFL doses significantly increased the metabolic activity of M. aeruginosa compared to a single high dose. Viability and cytoplasmic membrane were not affected by OFL exposure, but oxidative stress was observed with fluctuating responses.