title: Combined effects of two antibiotic contaminants on Microcystis aeruginosa.
abstract: Combined toxicity of spiramycin and amoxicillin was tested in Microcystis aeruginosa. The respective 50% effective concentrations (EC50mix) expressed in toxic unit (TU) values were 1.25 and 1.83 for spiramycin and amoxicillin mixed at 1:7 and 1:1, suggesting an antagonistic interaction at the median effect level. Deviations from the prediction of concentration addition (CA) and independent action (IA) models further indicated that combined toxicity of two antibiotics mixed at 1:1 varied from synergism to antagonism with increasing test concentration. Both the EC50mix of 0.86 (in TU value) and the deviation from two models manifested a synergistic interaction between spiramycin and amoxicillin mixed at 7:1. At an environmentally relevant concentration of 800ngL(-1), combined effect of mixed antibiotics on algal growth changed from stimulation to inhibition with the increasing proportion of higher toxic component (spiramycin). Chlorophyll-a content and expression levels of psbA, psaB, and rbcL varied in a similar manner as growth rate, suggesting a correlation between algal growth and photosynthesis under exposure to mixed antibiotics. The stimulation of microcystin-production by mixed antibiotics was related with the elevated expression of mcyB. The mixture of two target antibiotics with low proportion of spiramycin (<50%) could increase the harm of M. aeruginosa to aquatic environments by stimulating algal growth and production and release of microcystin-LR at their current contamination levels.
authors: Shandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Jinan 250100, PR China. Electronic address: liuying2010@sdu.edu.cn.
authors: Ying
authors: Y
authors: Liu
authors: Shandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Jinan 250100, PR China.
authors: Jian
authors: J
authors: Zhang
authors: Shandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Jinan 250100, PR China.
authors: Baoyu
authors: B
authors: Gao
authors: Shandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Jinan 250100, PR China.
authors: Suping
authors: S
authors: Feng
mesh_terms: D000658:Amoxicillin / Q000633:toxicity*; D000900:Anti-Bacterial Agents / Q000633:toxicity*; D002734:Chlorophyll / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005068:Eutrophication; D005786:Gene Expression Regulation / Q000187:drug effects; D046931:Microcystis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D015572:Spiramycin / Q000633:toxicity*
chemical_list: D000900:Anti-Bacterial Agents; D002734:Chlorophyll; D015572:Spiramycin; D000658:Amoxicillin
keywords: Amoxicillin; Gene transcription; Microcystin-LR; Photosystem; Spiramycin