Efficient degradation of ciprofloxacin and erythromycin coupled to elevated lipid synthesis in Synechococcus sp. and Chroococcus sp.

The variations of cell density, photosynthesis activity, biomass, lipid productivity, ultra-structure and metabolomic profile of two non-toxic cyanobacterial species, Synechococcus sp. and Chroococcus sp., during the degradation of two frequently detected antibiotics, ciprofloxacin and erythromycin, were investigated through a 4-day exposure test at antibiotic exposure doses of 0.2-20.0 mu g/L. Each target antibiotic induced hormetic effects on cell density and photosynthesis activity of each cyanobacterial species. The lipid productivity of Synechococcus sp. was elevated to 18.70 mg/L/d and 25.95 mg/L/d under exposure to ciprofloxacin and erythromycin, respectively. The lipid productivity of Chroococcus sp. was elevated to 26.25 mg/L/d and 22.85 mg/L/d by ciprofloxacin and erythromycin, respectively. The increase of cell weight or lipid content or both of them contributed to the elevation of lipid productivity. Increased number and size of lipid droplets were observed in cyanobacterial cells exposed to target antibiotics through transmission electron microscopy. Upregulation of monoacylglycerols and fatty acids were observed in cyanobacterial cells under antibiotic exposure through metabolomic analysis. Due to the cooperation of abiotic degradation, biosorption and biodegradation, Synechococcus sp. removed 48.72 %-64.71 % of ciprofloxacin and 43.22 %-82.43 % of erythromycin from the culture medium, and Chroococcus sp. removed 43.34 %-63.15 % of ciprofloxacin and 38.32 %-74.36 % of erythromycin. Several degradation products were identified for each antibiotic during the removal process by each cyanobacterial species. Results of this study demonstrated prospects for the utilization of non-toxic cyanobacteria in treating antibiotic-contaminated wastewater and meanwhile producing cyanobacterial biodiesel within a short culture period of 4 days.