Transcriptome analysis of changes in M. aeruginosa growth and microcystin production under low concentrations of ethinyl estradiol.

Ethinyl estradiol (EE2) is a synthetic environmental estrogen with considerable estrogenic activity. It has been found to consequently pose a significant threat to the aquatic ecosystem. Harmful algal blooms are a major aquatic ecological issue. However, the relationship between EE2 and cyanobacterial bloom is mainly unknown. In this study, the physiological and molecular responses of Microcystis aeruginosa to EE2 exposure were investigated. A low level of EE2 (0.02 µg/L) significantly enhanced the growth of algal cells (P < 0.05), whereas higher concentrations of EE2 (0.2-200 µg/L) inhibited it. EE2 at doses ranging from 0.02 to 200 µg/L promoted the production of microcystins (MCs), with genes mcyABD playing a key role in the regulation of MC synthesis. The alterations of chlorophyll-a, carotenoid, and phycocyanin contents caused by EE2 showed the same trend as cell growth. At the molecular level, 200 µg/L EE2 significantly down-regulated genes in photosynthetic pigment synthesis, light harvesting, electron transfer, NADPH, and ATP generation. High concentrations of EE2 caused oxidative damage to algal cells on the 4th d. After 12d exposure, although there was no significant change in superoxide dismutase (SOD) content and no damage observed in membrane lipids, genes related to SOD and glutathione were changed. In addition, due to the down-regulation of pckA, PK, gltA, nrtA, pstS, etc., carbon fixation, glycolysis, TCA cycle, nitrogen and phosphorus metabolism were hindered by EE2 (200 µg/L). Gene fabG in fatty acid biosynthesis was significantly up-regulated, promoting energy storage in cells. These findings provide important clues to elucidate the effects and mechanisms of cyanobacterial blooms triggered by EE2 and help to effectively prevent and control cyanobacterial blooms.

Environmental estrogens in surface water and their interaction with microalgae: A review.

Environmental estrogens (EEs) have received extensive attention because they interfere with biological endocrine and reproduction systems by mimicking, antagonizing, or otherwise affecting the actions of endogenous hormones. Additionally, harmful algal blooms have become a global problem in surface water. Microalgae, as an essential primary producer, is especially important for aquatic life and the entire ecosystem. The presence of EEs in surface water may be a potential promoting factor for algal blooms, and microalgae may have effects on the degradation of EEs. This review focuses on the distribution and pollution characteristics of EEs in global surface waters, effects of single and mixed EEs on microalgae regarding growth and toxin production, mechanisms of EEs on microalgae at the cellular and molecular level. The impacts of microalgae on EEs were also discussed. This review provides a risk assessment of EEs and identifies essential clues that will aid in formulating and revising the relevant standards of surface water regarding EEs, which is significant for ecosystems and human health.

Algae removal performance of UV-radiation-enhanced coagulation for two representative algal species.

Algal blooms severely impact the ecological environment and human health, as well as drinking water supplies and treatment systems. This study investigated UV-radiation-enhanced aluminum (Al)-based coagulation for the removal of two representative algal species (Microcystis aeruginosa and Cyclotella sp.) which are responsible for most fresh water algal bloom in different seasons. The results demonstrated that the UV-Al process can enhance algae removal, and simultaneously control algal organic matter (AOM) release. Comparing with Microcystis aeruginosa, Cyclotella sp. was more sensitive to UV irradiation and its activity was severely inhibited by 240 s of UV irradiation; intracellular reactive oxygen species (ROS) increased sharply then decreased rapidly, and SEM images showed cell walls exhibited substantial compression. UV irradiation decreased the zeta potential, which might have contributed to algae removal. Approximately 93.5% of Microcystis aeruginosa cells and 91.4% of Cyclotella sp. cells were removed after 240 s of UV irradiation with 0.4 mmol/L Al. The MCs concentrations after Al coagulation were low (<100 ng/L). The DOC of Microcystis aeruginosa and Cyclotella sp. was also lower (1.2 and 1.6 mg/L, respectively) than the national standard level after UV-Al process. This study highlights the practical application of UV irradiation for enhancing algae removal and simultaneously controlling AOM release in water treatment plants, which is a simple and promising technology. This result also indicates that the water treatment parameters should be adjusted according to the algae species present in different seasons, especially for diatom which needs low UV irradiation and Al dosage.

Removal of cyanobacteria and control of algal organic matter by simultaneous oxidation and coagulation - comparing the H2O2/Fe(II) and H2O2/Fe(III) processes.

Cyanobacterial blooms in drinking water are worldwide concern. It is known that pre-oxidation enhanced coagulation can be more efficient at removing algae than traditional coagulation. However, its application is hindered by high oxidant/coagulant consumption and the resultant potential health risk, in the form of algal organic matter (AOM) released during oxidation. To remove the cyanobacteria and meanwhile ensure cell integrity, H2O2/Fe(II) and H2O2/Fe(III), which have been widely used to degrade organic pollutants in waters, are proposed in this study. The removal efficiency of Microcystis aeruginosa (M. aeruginosa) under various oxidant/coagulant dosages, AOM release and cell integrity, as well as floc formation and morphology were investigated with these simultaneous oxidation/coagulation processes. The results show that the removal efficiency was higher than 95% with H2O2/Fe(II) and H2O2/Fe(III) under 100 µmol/L H2O2 and Fe. In addition, neither method was found to damage the algal cells in 50-200 µmol/L H2O2 dosing concentrations. It was also found that AOM, including microcystins (MCs), was well controlled owing to the oxidation of H2O2 or hydroxyl radicals, and in-situ Fe(III) settled down the cells in the processes. Compared with H2O2/Fe(II), H2O2/Fe(III) could remove algae efficiently and control AOM release with lower H2O2 (50 µmol/L) and Fe(III) (80 µmol/L) dosages, which suggests that a low chemical consumption is suitable for this simultaneous oxidation/coagulation processes. This is a promising technology for the removal of algae from drinking water in a clean, economical way.