Exposure of Microcystis aeruginosa to Hydrogen Peroxide under Light: Kinetic Modeling of Cell Rupture and Simultaneous Microcystin Degradation.

The effect of hydrogen peroxide on the cell integrity of a cyanobacterium, Microcystis aeruginosa, and on the release and degradation of microcystins (MCs) under simulated sunlight was investigated. The cyanobacterium was exposed to H2O2 in the range of 0-60 mg·L(-1) for 3.5 h. Production of OH radical in the solution was estimated by a chemical probe method. More than 99% (2 log) of the M. aeruginosa cells were ruptured or damaged by 3 h for all the treatments. Loss of cell integrity over time revealed two distinct phases. Cells retained their integrity during the initial lag phase and rapidly ruptured following first-order reaction afterward. A linear relationship was found between the duration of the lag phase and the steady-state concentration of OH radical. Release of MCs was closely correlated with the loss of cell integrity. Sequential reaction models were developed to simulate the release and degradation of MCs. These models were able to quantitatively describe the kinetics of all reactions under different H2O2 doses and extended exposure time. In particular, the models successfully predicted the concentration change of MCs using independently measured parameters. These models provide a simple and quantitative means to estimate the interaction of oxidants and cells and the consequent release of metabolites during oxidation treatment of cyanobacterium-laden waters.

Measurement of cyanobacteria using in-vivo fluoroscopy -- effect of cyanobacterial species, pigments, and colonies.

The effect of instrument calibration range, algal growth phase, chlorophyll-a and turbidity interference and colony size, on the measurement of phycocyanin by in-vivo fluoroscopy (IVF) was investigated. The cyanobacterial species Microcystis aeruginosa PCC 7820, Anabaena circinalis and Planktothricoides raciborskii were used to investigate variation in phycocyanin content in the different cyanobacteria and growth phases. The green alga, Chodatella sp., and Kaolin particles were used as the sources of chlorophyll-a and turbidity respectively to determine how these factors can impact on phycocyanin measurements. Another cyanobacterium, M. aeruginosa PCC 7005, which forms large colonies, was used to investigate the relationships between colony size and phycocyanin concentration measured using IVF. Results showed that chlorophyll-a, turbidity, and the colonial status of the cyanobacteria significantly interfered with the measurement of phycocyanin fluorescence. Models were developed to compensate for the effect of chlorophyll-a, turbidity and colony size on the measurement. The models were successfully used to correct phycocyanin probe data collected from several reservoirs in Taiwan to establish good correlation between measurements made using the phycocyanin probe and microscopic cell counts.

Kinetics of cell lysis for Microcystis aeruginosa and Nitzschia palea in the exposure to ß-cyclocitral.

The effect of an algal metabolite, ß-cyclocitral, on the cell integrity of two cyanobacteria and one diatom was investigated. The cyanobacteria, Microcystis aeruginosa PCC 7005 and PCC 7820, and the diatom, Nitzschia palea, were exposed to various concentrations of ß-cyclocitral. Scanning electron microscope (SEM) results indicate that the cells of tested species were greatly altered after being exposed to ß-cyclocitral. A flow cytometer coupled with the SYTOX stain and chlorophyll-a auto-fluorescence was used to quantify the effect of ß-cyclocitral on cell integrity for the tested cyanobacteria and diatom. Kinetic experiments show that about 5-10 mg L(-1) of ß-cyclocitral for the two M. aeruginosa strains and a much lower concentration, 0.1-0.5 mg L(-1), for N. palea were needed to cause 15-20% of cells to rupture. When the ß-cyclocitral concentration was increased to 200-1000 mg L(-1) for M. aeruginosa and 5-10 mg L(-1) for N. palea, almost all the cells ruptured between 8 and 24h. A first-order kinetic model is able to describe the data of cell integrity over time. The extracted rate constant values well correlate with the applied ß-cyclocitral dosages. The obtained kinetic parameters may be used to estimate ß-cyclocitral dosage and contact time required for the control of cyanobacteria and diatoms in water bodies.