title: Extracellular polymeric substances buffer against the biocidal effect of H2O2 on the bloom-forming cyanobacterium Microcystis aeruginosa.
abstract: H2O2 is an emerging biocide for bloom-forming cyanobacteria. It is important to investigate the H2O2 scavenging ability of extracellular polymeric substances (EPS) of cyanobacteria because EPS with strong antioxidant activity may "waste" considerable amounts of H2O2 before it kills the cells. In this study, the buffering capacity against H2O2 of EPS from the bloom-forming cyanobacterium Microcystis aeruginosa was investigated. IC50 values for the ability of EPS and vitamin C (VC) to scavenge 50% of the initial H2O2 concentration were 0.097 and 0.28 mg mL(-1), respectively, indicating the higher H2O2 scavenging activity of EPS than VC. Both proteins and polysaccharides are significantly decomposed by H2O2 and the polysaccharides were more readily decomposed than proteins. H2O2 consumed by the EPS accounted for 50% of the total amount of H2O2 consumed by the cells. Cell growth and photosynthesis were reduced more for EPS-free cells than EPS coated cells when the cells were treated with 0.1 or 0.2 mg mL(-1) H2O2, and the maximum photochemical efficiency Fv/Fm of EPS coated cells recovered to higher values than EPS-free cells. Concentrations of H2O2 above 0.3 mg mL(-1) completely inhibited photosynthesis and no recovery was observed for both EPS-free and EPS coated cells. This shows that EPS has some buffering capacity against the killing effect of H2O2 on cyanobacterial cells. Such a strong H2O2 scavenging ability of EPS is not favorable for killing bloom-forming cyanobacteria. The high H2O2 scavenging capacity means considerable amounts of H2O2 have to be used to break through the EPS barrier before H2O2 exerts any killing effects on the cells. It is therefore necessary to determine the H2O2 scavenging capacity of the EPS of various bloom-forming cyanobacteria so that the cost-effective amount of H2O2 needed to be used for killing the cyanobacteria can be estimated.
authors.affiliation: Xinjiang Key Laboratory of Environmental Pollution and Bioremediation, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China; Graduate University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Gao
authors.affiliation: Xinjiang Key Laboratory of Environmental Pollution and Bioremediation, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China. Electronic address: xlpan@ms.xjb.ac.cn.
authors.forename: Xiangliang
authors.initials: X
authors.lastname: Pan
authors.affiliation: Xinjiang Key Laboratory of Environmental Pollution and Bioremediation, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China; State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China. Electronic address: zhang-daoyong@163.com.
authors.forename: Daoyong
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Xinjiang Key Laboratory of Environmental Pollution and Bioremediation, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China.
authors.forename: Shuyong
authors.initials: S
authors.lastname: Mu
authors.affiliation: Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan.
authors.forename: Duu-Jong
authors.initials: DJ
authors.lastname: Lee
authors.affiliation: College of Resource and Environment Sciences, Xinjiang Key Laboratory of Oasis Ecology, Xinjiang University, Urumqi 830046, China.
authors.forename: Umut
authors.initials: U
authors.lastname: Halik
mesh_terms: D001205:Ascorbic Acid / Q000494:pharmacology; D001704:Biopolymers / Q000494:pharmacology*; D004202:Disinfectants / Q000494:pharmacology*; D005068:Eutrophication / Q000187:drug effects*; D005110:Extracellular Space / Q000737:chemistry*; D016166:Free Radical Scavengers / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007700:Kinetics; D046931:Microcystis / Q000187:drug effects* / Q000378:metabolism; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000187:drug effects; D045332:Photosystem II Protein Complex / Q000378:metabolism; D013050:Spectrometry, Fluorescence
chemical_list: D001704:Biopolymers; D004202:Disinfectants; D016166:Free Radical Scavengers; D045332:Photosystem II Protein Complex; D006861:Hydrogen Peroxide; D001205:Ascorbic Acid
keywords: Antioxidant; Biocide; Bloom; Exopolymer; Exopolysaccharide; Photosynthesis