Antibiotics induced alterations in cell density, photosynthesis, microcystin synthesis and proteomic expression of Microcystis aeruginosa during CuSO4 treatment

Abstract

Antibiotic contaminants have the potential to interfere with the control of cyanobacterial bloom through generating hormesis in cyanobacteria at current contamination level of ng L−1. This study investigated the influence of a mixture of four frequently detected antibiotics, amoxicillin, ciprofloxacin, sulfamethoxazole and tetracycline, during the treatment of Microcystis aeruginosa by copper sulfate (CuSO4) algaecide. CuSO4 significantly (p < 0.05) inhibited cell density, growth rate, Fv/Fm value, chlorophyll a content and microcystin production ability of M. aeruginosa in a dose-dependent manner at application doses of 0.01-0.05 mg L−1. Besides, CuSO4 inhibited oxidation-reduction process, photosynthesis and biosynthesis in M. aeruginosa at the proteomic level. Preventative application of CuSO4 to a low density (4 × 105 cells mL−1) of M. aeruginosa effectively prevented the formation of bloom at low CuSO4 doses, which is a possible route for eliminating the negative effects of CuSO4 algaecide in aquatic environments. The presence of mixed antibiotics alleviated the toxicity of CuSO4 in M. aeruginosa, through the downregulation of cation transport proteins and the upregulation of proteins related with chlorophyll a synthesis, photosynthesis, gene expression and oxidation-reduction. Mixed antibiotics also promoted microcystin synthesis in CuSO4 treated cells through the upregulation of microcystin synthetases. Mixed antibiotics significantly (p < 0.05) increased cell density, growth rate, Fv/Fm value, chlorophyll a content and microcystin production ability in CuSO4 treated cells at test concentrations of 80 and 200 ng L−1. A no-impact threshold of 20 ng L−1 for mixed antibiotics (5 ng L−1 for each antibiotic) was suggested for eliminating the interference of antibiotic contaminants on cyanobacterial bloom control.