环境地球化学国家重点实验室知识库

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 Microcystisaeruginosa 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.