Study The Response Of Freshwater Microalgae To Several Antibiotics Stress

Antibiotics have been widely used in people’s life, but because the phenomenonof misusing and abusing of antibiotics intensifies and the mismanaging of antibiotics,thus leading to a large number of antibiotics enter into the water, which willinevitably affect the microalgae in water body, thereby affecting the entire aquaticecosystems. In order to investigate the effects and mechanism of antibiotics on theprimary producers (algae) in aquatic ecosystems and accurately assess the ecologicalrisks caused by antibiotics, this research chose levofloxacin, ofloxacin anderythromycin as target compounds, used Chlorella pyrenoidosa (green algae) andMicrocystis flos-aquae (cyanobacteria) as tested subjects, investigated the mechanismof freshwater microalgae in response to three antibiotics stress by determining thegrowth, physiological and biochemical characteristic, photosynthetic activity, cellcycle and apoptosis of two microalgae. The results indicated:(1) Three antibiotics had shown a "low concentrations promotion and highconcentrations inhibition" phenomenon on the growth of two microalgae. When theconcentrations of three antibiotics were below0.1μg/L, promoted the growth ofMicrocystis flos-aquae, while inhibiting the growth once the concentration wasgreater than10μg/L; when the concentrations of levofloxacin, ofloxacin,erythromycin were less than1mg/L,10mg/L and10-2mg/L, separately, the growthof Chlorella pyrenoidosa was promoted, and was inhibited in higher than10mg/L.The inhibition of erythromycin on two microalgae was higher than levofloxacin andofloxacin, and Microcystis flos-aquae was more sensitive than Chlorella pyrenoidosato three antibiotics.(2) Under the single and combined effects of high concentrations of threeantibiotics (>1μg/L and10mg/L), antioxidant enzyme activities of two microalgaewere significantly induced, malondialdehyde content also significantly increased,caused severe oxidative stress, and the algae growth were inhibited. However, underthe effects of low concentrations of antibiotics (<1μg/L and10mg/L), the antioxidantsystem of two microalgae had no significant change. (3) After exposure to low concentrations of three antibiotics (<1μg/L), thechlorophyll a content and photosynthetic activity of Microcystis flos-aquae wereincreased. While under the stress of high concentrations (>10μg/L), the algae cellwas serious damaged, photosynthetic activity and electron transfer were stronglysuppressed. For Chlorella pyrenoidosa, lower concentrations of levofloxacin andofloxacin (<1mg/L) stimulated its electron transfer and energy utilization efficiency,and under the stress of high concentrations (10mg/L and100mg/L), photosyntheticsystem occurred reversible inactivation; lower concentrations of erythromycin (<1mg/L) had no obvious effects on the photosynthetic system of Chlorella pyrenoidosa,while high concentrations of erythromycin (≥10mg/L) severely damaged thephotosynthetic organs, reduced the energy utilization efficiency and electron transferrate, resulted in irreversible inactivation of photosynthesis II.(4) When lower concentrations of levofloxacin and erythromycin mixed,weakened the promotion when two antibiotics single acted on Microcystis flos-aquae,the photosynthetic activity also reduced; after mixing the high concentrations of twoantibiotics, the inhibitory effect on photosynthetic activity of Microcystis flos-aquaewas aggravated. For Chlorella pyrenoidosa, the impact caused by two antibioticsmixture almost consistent with the effect of erythromycin signle action, indicatingthat erythromycin may play a major role in the combined effect of two antibiotics.(5) The lower concentrations of three antibiotics (≤1μg/L and1mg/L) had noeffects on cell cycle and apoptosis of two microalgae. However, high concentrationsof three antibiotics (>1μg/L and1mg/L) inhibited the DNA synthesis, cell divisionand proliferation of algae cells, and apoptosis also increased significantly, showed adose-response relationship.