chlorophyll-a and beta-cyclocitral

The cyanobacterium Microcystis produces volatile organic compounds such as β-cyclocitral and 3-methyl-1-butanol. The lysis of cyanobacteria involving the blue color formation has been occasionally observed in a natural environment. In this study, we focused on the oxidation behavior of β-cyclocitral that contributed to the blue color formation in a natural environment and compared β-cyclocitral with a structurally related compound concerning its oxidation, acidification, and lytic behavior. The oxidation products of β-cyclocitral were identified by the addition of β-cyclocitral in water, in which 2,2,6-trimethylcyclohex-1-ene-1-yl formate and 2,2,6-trimethylcyclohexanone were structurally characterized. That is, β-cyclocitral was easily oxidized to produce the corresponding carboxylic acid and the enol ester in water without an oxidizing reagent, suggesting that this oxidation proceeded according to the Baeyer-Villiger oxidation. The oxidation behavior of β-cyclocitral in a laboratory was different from that in the natural environment, in which 2,2,6- trimethylcyclohexanone was detected at the highest amount in the natural environment, whereas the highest amount in the laboratory was β-cyclocitric acid. A comparison of β-cyclocitral with structurally similar aldehydes concerning the lytic behavior of a Microcystis strain and the acidification process indicated that only β-cyclocitral was easily oxidized. Furthermore, it was found that a blue color formation occurred between pH 5.5 and 6.5, suggesting that chlorophyll a and β-carotene are unstable and decomposed, whereas phycocyanin was stable to some extent in this range. The obtained results of the characteristic oxidation behavior of β-cyclocitral would contribute to a better understanding of the cyanobacterial life cycle.

Topics: Aldehydes; beta Carotene; Chlorophyll; Chlorophyll A; Color; Diterpenes; Hydrogen-Ion Concentration; Microcystis; Oxidation-Reduction; Pentanols

Lake Dianchi is the sixth largest freshwater lake in China. The pilot experimental area (6 km2) in Lake Dianchi is one of the most severely polluted areas in the lake with heavy cyanobacteria blooms. During June 2002 to May 2003, the algal composition and number, and odorous compounds were identified monthly and monitored in the area. Meanwhile, physicochemical parameters such as total phosphorus (TP), total nitrogen (TN), 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD(Mn)), dissolved oxygen (DO), pH, transparency, temperature and chlorophyll a (chla) were determined. Four odorous compounds: 2-methylisoborneol (MIB), geosmin, beta-cyclocitral and beta-ionone were found in the lake water. Both the concentration of particulate beta-cyclocitral and that of beta-ionone correlated significantly with the annual variation of Chla, biomass of total phytoplankton, cyanobacteria and Microcystis. The concentration of particulate MIB correlated significantly with the biomass of Oscillatoria, while the concentration of particulate geosmin correlated significantly with the biomass of Anabaena. Off-flavour in the pilot area was found to be caused by a combination of beta-cyclocitral- and beta-ionone-producing Microcystis, MIB-producing Oscillatoria and geosmin-producing Anabaena. beta-ionone, MIB and geosmin contributed collectively to the odour intensity in the lake water.

Topics: Aldehydes; Camphanes; China; Chlorophyll; Chlorophyll A; Diterpenes; Environmental Monitoring; Eutrophication; Fresh Water; Naphthols; Nitrogen; Norisoprenoids; Oxygen; Phosphorus; Phytoplankton; Water Pollutants, Chemical; Water Purification