Effects of minocycline and its degradation products on the growth of Microcystis aeruginosa

This work aimed to investigate the influence of Microcystis aeruginosa on the rate of minocycline (MNC) removal (abiotic degradation, physical binding or chemical transformation by cells) and the toxicity of MNC and its degradation products to the cyanobacterium. Most of the work was carried out in culture media in the presence or in the absence of M. aeruginosa. The rate of the MNC abiotic degradation in culture media strongly decreased with the increase of the MNC initial concentration. The exudates did not influence the rate of MNC degradation in the media. For concentrations ≥0.48 μM, the rate of the MNC removal from the media was faster in the presence of M. aeruginosa. Biotic MNC removal occurs by both physical binding by the cells (10%) and chemical transformations. EC50 and EC20 for MNC on the growth of M. aeruginosa were 0.92 and 0.13 μM, respectively. Interestingly, MNC degradation products might promote M. aeruginosa growth.