The effect of an algal metabolite, beta-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 beta-cyclocitral. Scanning electron microscope (SEM) results indicate that the cells of tested species were greatly altered after being exposed to beta-cyclocitral. A flow cytometer coupled with the SYTOX stain and chlorophyll-a auto-fluorescence was used to quantify the effect of beta-cyclocitral on cell integrity for the tested cyanobacteria and diatom. Kinetic experiments show that about 5-10 mg L-1 of beta-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 beta-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 24 h. 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 beta-cyclocitral dosages. The obtained kinetic parameters may be used to estimate beta-cyclocitral dosage and contact time required for the control of cyanobacteria and diatoms in water bodies. (C) 2010 Elsevier B.V. All rights reserved.