Effects Of Tetracyclines And Sulfonamides On Microcystis Aeruginosa And Chlamydomonas Microsphaera

In recent years,the abuse of antibiotics has become one of the major environmental problems.The report on the detection of antibiotics in the surface water is endless,and the ecological security,health and safety problems have been paid more and more attention.Microalgae is a widely occurring eukaryotic organism in natural water.It is one of the most sensitive species to the effects of pollutants.It is commonly used in toxicological studies of harmful substances.As primary producer,algae is the basis for the survival of other organisms in the water and plays a very significant role in the food chain and water ecosystem.Tetracyclines and sulfonamides are two kinds of antibiotics with high detection rate in surface water.Microcystis aeruginosa and Chlamydomonas microsphaera are two dominant algae species in surface water.In this study,the toxicity of four antibiotics to M.aeruginosa and C.microsphaera was studied by laboratory simulation.The aim of this study was to evaluate the effect of antibiotics on algal growth,physiological characteristics and population changes and analyze the mechanism of antibiotics on algae growth,as well as provide the theoretical basis for evaluation of antimicrobial contamination.The effect of antibiotic compound effect on the growth of algae was also studied.The main research results are as follows:1.After the effect of 96 h single antibiotics on single species,there was a dose–response relationship between M.aeruginosa and C.microsphaera characterized by low-dose(less than 0.5 mg/L)stimulation and high-dose(more than 1 mg/L)inhibition.The 96 h EC50 of tetracycline and oxytetracycline on M.aeruginosa was 10.394 and 7.246 mg/L,and the maximum inhibitory rate of sulfonamides in the designed concentration range was 30%.The 96 h EC50 of tetracycline,oxytetracycline,sulfadiazine and sulfamethoxazole on C.microsphaera was 2.038?4.196?10.425?3.564 mg/L,which indicating that M.aeruginosa was more resistant to antibiotics than C.microsphaera.The effect of tetracyclines on algae growth and photosynthesis is greater than that of sulfonamides.Tetracycline antibiotics inhibit the growth of algae by destroying the cell membrane structure,while the sulfa antibiotics suppress algal growth by altering the permeability of the cell membrane.With the increase of the concentration of antibiotics,the increase of the content of superoxide dismutase indicates that the pollutants stimulate the antioxidant reaction,but the increase of the malondialdehyde content indicates that the superoxide dismutase is insufficient to eliminate the superoxide anion of persecuted cells.The antibiotics in surface waters do not reach the concentrations required for toxicity in algae,but the low-dose stimulation of algae should be considered in severely eutrophic waters.2.Low concentration of tetracycline and oxytetracycline(0.1 mg/L)promoted the growth of algae,and high concentration(more than 1 mg / L)inhibit the growth of algae under the condition of single culture and co-culture.Under the influence of antibiotics,the two kinds of algae had a synergistic effect in co-culture to resist the persecution of pollutants.M.aeruginosa had a strong inhibitory effect on C.microsphaera,while the inhibitory effect of C.microsphaera on M.aeruginosa was small.Under the influence of oxytetracycline and tetracycline,the competition relationship between algae species was changed and the algae population structure was changed,which promoted M.aeruginosa to become a dominant population.3.Under the influence of mixed antibiotics,the tolerability of M.aeruginosa was higher than that of C.microsphaera.According to the standards set by the European Union,oxytetracycline is toxic to M.aeruginosa,sulfamethoxazole and the mixed antibiotic are harmful to M.aeruginosa.Oxytetracycline,sulfamethoxazole and the mixture of antibiotics are toxic pollutants to C.microsphaera.The combined effect of tetracycline and oxytetracycline was partly additive to C.microsphaera and antagonistic to M.aeruginosa.There was a positive correlation between chlorophyll a content and algal biomass.When the concentration of mixed antibiotics was 0.5 mg/L,the chlorophyll a content reached the maximum.The assessments of the antibiotic risk of M.aeruginosa and C.microsphaera found that antibiotics in farm wastewater could pose a threat to the ecological environment.When assessing the impact of pollutants on the environment,a variety of organisms should be selected as the indicator organisms,and the multiple assessment methods should be analyzed to make assessment of pollutants.