iTRAQ-based quantitative proteomic analysis of Microcystis aeruginosa exposed to spiramycin at different nutrient levels

Research on the combined effects of antibiotic contaminants and environmental factors in cyanobacteria is still limited. This study focused on the action and its mechanism of spiramycin combined with changes in nitrogen and phosphorus level in Microcystis aeruginosa at environmentally relevant concentrations. Though photosynthetic activity was stimulated by spiramycin at a high nutrient level, no significant correlation (p > 0.05) was found between photosynthesis-related proteins and growth-related proteins, and the growth rate was inhibited by 200 ng L−1 of spiramycin. At low nitrogen and low phosphorus levels, up-regulated photosynthesis-related proteins were closely correlated with (p < 0.05) stress response-related, transcription-related and cell division-related proteins, which consequently led to stimulated growth of M. aeruginosa under spiramycin exposure. Spiramycin exposure also regulated the production of microcystins (MCs) and the expression of two microcystin synthetases (mcyB and mcyC). The spiramycin-induced protein secretion process and the up-regulation of ATP binding cassette transporters might contribute to the increased MC release. Enolase, superoxide dismutase, protein GrpE, DNA-directed RNA polymerase subunit alpha and serine protease were candidate target proteins of spiramycin in M. aeruginosa under different nutrient conditions. Coexisting spiramycin mitigated the threat of cyanobacteria to aquatic environments at a high nutrient level but aggravated cyanobacterial bloom at a low nitrogen level.