title: Changes in the physiology and gene expression of Microcystis aeruginosa under EGCG stress.
abstract: EGCG (Epigallocatechin-3-gallate) has an allelopathic inhibitory effect on Microcystis aeruginosa. Cellular structure, physiological and biochemical reactions and gene expression were examined to explore the mechanism of inhibition. As was shown in electron microscopy, the structure of the cell wall, cell membrane and thylakoid was disrupted by EGCG. EGCG also reduced the efficiency of photosynthesis and the electron transfer rate in M. aeruginosa cells, as was determined with a flow cytometer. Quantitative real-time PCR analysis demonstrated that gene expression of the core proteins of the photosynthesis centers PSI and PSII and ATP synthase were reduced, while the expression of the phycobilisome degradation protein A gene (nbl A) was elevated. The expression of the universal stress protein gene increased, which would enhance the adaptive capacity of Microcystis cells to polyphenols and oxidative stress. Furthermore, EGCG elevated the level of reactive oxygen species (ROS) in M. aeruginosa cells, and thus caused oxidative cellular damage. When treated with EGCG at low concentrations (10 and 40 mg L(-)(1)), the cells were able to activate defense systems to degrade the excess ROS. But at a concentration of 70 mg L(-)(1), oxidative stress exceeded tolerance limits, and the cells were severely damaged. We concluded that damage to photosynthesis and oxidative stress were the primary mechanisms for the allelopathic effect of EGCG on M. aeruginosa.
authors.affiliation: Biological Experiment Teaching Center, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China; State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: lyphwq@njau.edu.cn.
authors.forename: Yaping
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Biological Experiment Teaching Center, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China. Electronic address: Wangjinhn@njau.edu.cn.
authors.forename: Jin
authors.initials: J
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: yyu@niglas.ac.cn.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yu
authors.affiliation: State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: lmshi@niglas.ac.cn.
authors.forename: Limei
authors.initials: L
authors.lastname: Shi
authors.affiliation: State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: fxkong@niglas.ac.cn.
authors.forename: Fanxiang
authors.initials: F
authors.lastname: Kong
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D046931:Microcystis / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D018384:Oxidative Stress / Q000187:drug effects; D010788:Photosynthesis / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D000900:Anti-Bacterial Agents; D017382:Reactive Oxygen Species; D002392:Catechin; C045651:epigallocatechin gallate
keywords: EGCG; Inhibitory mechanism; Microcystisaeruginosa; Real-time PCR; Tea polyphenol