Toxic Effects And Its Mechanism Of Erythromycin, Ciprofloxacin And Sulfamethoxazole To Selenastrum Capricornutum

The ecological effects of antibiotics have attracted increasing attentions from both public and environmental fields due to its widespread usage and the improper disposal. In order to investigate the toxic mechanism and evaluate the ecological risk of antibiotics to photosynthetic organisms, three widely used antibiotics, erythromycin, ciprofloxacin and sulfamethoxazole were chosen to be target compounds and Selenastrum capricornutum, a model algae, was used as tested object to evaluate the effects of those antibiotics on growth and physiological metabolism of algae through the following aspects:growth rate, chlorophyll biosynthesis, photosynthetic apparatus, secondary metabolism, antioxidation system and cytochrom P450 system. The results indicated:(1) The toxicity of erythromycin was higher than ciprofloxacin and sulfamethoxazole, their 96 h IC50 were 0.20,3.07 and 4.40 mg L-1, respectively; and the safe concentration were 0.019,0.297 and 0.312 mg L-1, respectively. (2) Three types of antibiotics could significantly decrease chlorophyll content. Erythromycin could induce decreasing of chlorophyll content at the concentration of 0.06 mg L-1, while ciprofloxacin and sulfamethoxazole achieved the same results at higher than 1.5 mg L-1. Otherwise, only erythromycin could significantly inhibit the chlorophyll biosynthesis at the first step (synthesis ofδ-aminolevulinic acid). (3) Three antibiotics could significantly inhibit the physiological metabolism process including primary photochemistry, electron transport, photophosphorylation and carbon assimilation. Erythromycin could bring about acute toxic effects at the concentration of 0.06 mg L-1, while the same results were exhibited for ciprofloxacin and sulfamethoxazole at higer than 1.0 mg L-1. (4) The secondary metabolism of S. capricornutum could be affected strikingly by three antibiotics. The phenylalanine ammonialyase activity and the content of each secondary metabolic product were decreased after erythromycin treatment, but increased after ciprofloxacin and sulfamethoxazole treatments. The flavonoids content was decreased significantly after erythromycin treatment. The phenylpropanoids, flavones and flavanols were more sensitive to ciprofloxacin than sulfamethoxazole, however, the anthocyanins was more sensitive to sulfamethoxazole than ciprofloxacin. (5) All three types of antibiotics could significantly affect the antioxidant system in S. capricornutum. Erythromycin could significantly induce oxidative stress and lead to the increase of the lipid peroxidation at the concentration of 0.06 mg L-1, while ciprofloxacin and sulfamethoxazole induced significant oxidative stress at concentrations higher than 1.0 and 1.5 mg L-1, respectively. Erythromycin was the most toxic to S. capricornutum mainly due to its inhibited effects on ascorbic acid and glutathione biosynthesis. In comparison, S. carpricornutum was more tolerant to ciprofloxacin and sulfamethoxazole. The tolerant of S. carpricornutum to ciprofloxacin were probably due to the induction of ascorbate-glutathione cycle and some other antioxidants, such as catalase and superoxide dismutase and sulfamethoxazole, while the tolerant of S. carpricornutum to sulfamethoxazole might be attributed to the induction of xanthophylls cycle and glutathione-S-transferase activity. (6) The effects of three antibiotics on cytochrome P450 system exhibited great diversity. Erythromycin could induce great inhibited effects on cytochrome P450 system while its treatment concentration was higher than 0.12 mg L-1; ciprofloxacin could inhibit the activities of enzymes related to the metabolism of xenobiotics, but no significant effects on the enzymes related to endogenuous substances metabolism and total cytochrome P450 contents; Sulfamethoxazole could induce activation effects on cytochrome P450 system including total cytochrome P450 contents and related enzymes activities. Overall, erythromycin was considerably more toxic than ciprofloxacin and sulfamethoxazole to tested algae and may pose a higher potential risks to the aquatic ecosystem. Some indices like chlorophyll fluorescence, activities of ribulose-1,5-bisphosphatecarboxylase, phenylalanin ammonialyase and cinnamic acid 4- hydroxylase showed a high sensitivity to the exposure of erythromycin, and may be potentially used as candidate biomarkers for macrolide antibiotics pollutions.