Delayed Signs of UV-C Damage to <i>Chlorella</i> sp. Observed through Fluorescent Staining

Ultraviolet (UV-C) irradiation is the most important part of water filtration, which has no side effects on the environment and has been used in water purification systems in the aquaculture and transistor industries. In this research, the effect of UV-C on Chlorella sp. was investigated. Chlorella sp. was irradiated 0, 1, 2 or 3 times at a fixed flow rate of 6.5 L min−1 and the effects of UV-C LED on the apoptosis rate and death rate of Chlorella sp. were analyzed by flow cytometry after staining cells with the nucleic acid dye SYTOX Green and the membrane-associated protein stain Annexin V-PE Reagent. As a result of UV-C irradiation, the Chlorella sp. cells underwent phosphatidylserine (PS) ectropion and plasma membrane damage, which resulted in death. The effect of UV-C was proportional to the number of times of irradiation. Three doses of UV-C LED irradiation resulted in a 91.76 ± 3.33% death rate, as observed through SYTOX Green staining, with no rebound within 72 h. This research is the first report to observe that delayed cellular apoptosis occurred in Chlorella sp., and we expect that our study can be used as a standard reference for future industrial applications