The effects of sub-lethal UV-C irradiation on growth and cell integrity of cyanobacteria and green algae

The effects of UV-C irradiation on algal growth and cell integrity were investigated to develop a potential method for preventing cyanobacterial blooms. The toxic cyanobacterium Microcystis aeruginosa and three common freshwater green algae Chlorella ellipsoidea, Chlorella vulgaris, and Scenedesmus quadricanda were exposed to UV-C irradiation at 0–200 mJ cm−2 and subsequently incubated for 9–15 d under normal culture conditions. Cell density and cell integrity were assessed using flow cytometry. The results suggested that UV-C irradiation at 20–200 mJ cm−2 can suppress M. aeruginosa growth for 3–13 d in a dose-dependent manner. UV-C irradiation at 20 and 50 mJ cm−2 is sub-lethal to M. aeruginosa cells as over 80% of the exposed cells remained intact. However, UV-C irradiation at 100 and 200 mJ cm−2 induced severe cell disintegration in more than 70% of the irradiated cells. Neither significant suppression nor disintegration effects on green algae were observed for UV-C irradiation at 20–200 mJ cm−2 in this study. Taken together, the sensitivity of M. aeruginosa to UV-C irradiation was significantly higher than that of the non-toxic C. ellipsoidea, C. vulgaris, and S. quadricauda, suggesting the potential application of sub-lethal UV-C irradiation for M. aeruginosa bloom control with a predictable low ecological risk.