The Different Responses Of Microcystis Aeruginosa And Scenedesmus Quadricanda On Typical Emerging Contaminants

In recent years, the emerging organic pollutants, such as polycyclic aromatic hydrocarbons and antibiotics, have attracted much attention because of their remarkable ecological and toxicological effects. And the response of algae and other phytoplankton to such pollution is relatively fast, and the influence of emerging organic pollutants on phytoplankton is different. The pollution status of emerging pollutants in Dianchi is not clear. Polycyclic aromatic hydrocarbons and other emerging organic pollutants may change the community structure of phytoplankton in eutrophic lakes. However, these problems in the related research in Dianchi involved less. Scenedesmus quadricanda is the dominant species of chlorophyta in Dianchi lake. Microcystis aeruginosa is the dominant species of cyanophyta in Dianchi lake. Scenedesmus quadricanda and Microcystis aeruginosa are the research object in this study. To investigate the stress response differences between Scenedesmus quadricanda and Microcystis aeruginosa on the Dianchi common emerging organic pollutants phenanthrene, norfloxacin and fluconazole.The results show:(1) In biomass (OD), PHEN had a significant inhibitory effect on cyanobacteria and chlorophyta. The inhibition of chlorophyta was significantly higher than that of cyanobacteria. At the concentration of 2000μg/L PHEN treated 72h, the inhibition rate (IR value) of PHEN on the growth of Microcystis aeruginosa and Scenedesmus quadricanda were 74% and 25%. Norfloxacin can significantly inhibit the growth of cyanobacteria, but has no effect on chlorophyta. Concentration of 50ug /L of NFLX treatment for 72 h, the inhibition on the growth of Microcystis aeruginosa rate is 78%, and the inhibition of Scenedesmus quadricauda rate is-6%. FCZ has a significant inhibitory effect on cyanobacteria and green algae, but the sensitivity of chlorophyta is much higher than that of cyanobacteria. Concentration of 10mg/L of FCZ treatment for 72 h,the inhibition rate of Scenedesmus quadricauda is 54%, and the inhibition rate of Microcystis aeruginosa is 16%.(2) From the point of view of photosynthesis (chlorophyll a content), The lower concentration of PHEN (100μg/L) had a significant promoting effect on the chlorophyll a content of the two species of algae. Higher concentrations (1000μg/L) of PHEN significantly inhibited Microcystis aeruginosa chlorophyll a content (IR48h =33.9%), but significantly promote the Scenedesmus quadricauda chlorophyll a content (IR48h=-20.3%). The concentration of NFLX stress significantly inhibited cyanobacteria chlorophyll a content, but chlorophyta is not affected. Low concentration of fluconazole (0.05mg/L) on the content of chlorophyll a of chlorophyta and cyanobacteria have a certain role in promoting. Concentration of 50μg/L of FCZ treatment for 48 h, The content of chlorophyll a in the content of Microcystis aeruginosa is significantly promoted (IR=-24%), while that of Scenedesmus quadricanda is significantly inhibited (IR=32%).(3) From oxidative stress (MDA content and Superoxide anion) point of view, Under PHEN stress, The cell membrane damage degree of Microcystis aeruginosa was significantly higher than that of Microcystis aeruginosa.Microcystis aeruginosa cell lipid over oxidation of PHEN stress response time (24 hours) as early as Scenedesmus quadricauda to PHEN stress response time (48h).2000ug/L of PHEN at 24h, MDA (0.14nmol/ml) produced by Microcystis aeruginosa was significantly higher than that produced by Scenedesmus quadricauda (0.08 nmol/ml).2000μg/L of PHEN at 72h,superoxide anion (13U/L) produced by Microcystis aeruginosa was significantly higher than that produced by Scenedesmus quadricauda (12U/L) under NFLX stress, Microcystis aeruginosa cell membrane damage is far greater than Scenedesmus quadricauda.50μg/L of NFLXat 48h,MDA (0.279nmol/ml) produced by Microcystis aeruginosa was significantly higher than that produced by Scenedesmus quadricauda(0.124 nmol/ml).And at this time the same concentration superoxide anion (13U/L) produced by Microcystis aeruginosa was significantly higher than that produced by Scenedesmus quadricauda (11U/L). Under FCZ stress, the cell membrane damage degree of Microcystis aeruginosa is significantly less than that of the Scenedesmus quadricauda.1 Omg/L of FCZ at 72h, MDA (0.117nmol/ml) produced by Microcystis aeruginosa was significantly lower than that produced by Scenedesmus quadricauda(0.147 nmol/ml). And at this time the same concentration superoxide anion produced by two kinds of algae are the same.(4) From the antioxidant system (SOD activity and soluble protein) point of view, Microcystis aeruginosa SOD activity of PHEN stress response time (24h) as early as Scenedesmus quadricauda to PHEN stress response time (48h). But Microcystis aeruginosa SOD activity has weakened even lost by 1000μg/L PHEN stress over time. The soluble protein content of Microcystis aeruginosa was significantly inhibited at this concentration.While Scenedesmus quadricauda SOD activity only in 2000μg/L PHEN stress showed a weakening. The soluble protein content of Scenedesmus quadricauda under this concentration showed a slow upward trend. Microcystis aeruginosa SOD activity after different concentration stress at 48h stress increased, then decreased. While Scenedesmus quadricauda affected by stress between NFLX groups of SOD activity and soluble protein had no significant change. Microcystis aeruginosa SOD activity of FCZ stress response time (48 h) is later than Scenedesmus quadricauda to FCZ stress response time (24 h). And the SOD activity of Scenedesmus quadricauda was weakened or even lost when Scenedesmus quadricauda was stressed by the 0.5mg/L of FCZ. However, Microcystis aeruginosa SOD activity only in 10mg/L FCZ stress showed a weakened phenomenon. It is further explained that Scenedesmus quadricauda are more sensitive to FCZ than Microcystis aeruginosa. Soluble protein content of two species of algae increased with the passage of time, and the increase of total amount of Microcystis aeruginosa was greater than Scenedesmus quadricauda.(5) Microcystis aeruginosa on NFLX and FCZ sensitive is PHEN> FCZ. Therefore, Microcystis aeruginosa on sensitivity of three kinds of pollutants from large to small is NFLX> PHEN> FCZ.Scenedesmus quadricauda on sensitivity of three kinds of pollutants from large to small is FCZ> PHEN> NFLX. For PHEN, Microcystis aeruginosa is more sensitive; for NFLX, Microcystis aeruginosa is more sensitive; for FCZ, Scenedesmus quadricauda is more sensitive.To sum up, the three typical emerging organic pollutants have great influence on the effect of cyanobacteria(Microcystis aeruginosa) and green algae(Scenedesmus quadricauda).These results provide a theoretical basis for revealing the structure of the organic pollutants in Dianchi. It also provides practical guidance for the further treatment of cyanobacteria bloom in Dianchi.