Effect of Viral Infection on the Functioning and Lysis of Black Sea Microalgae Tetraselmis viridis (Chlorophyta) and Phaeodactylum tricornutum (Bacillariophyta)

Experimental studies have been performed on Tetraselmis viridis (Rouchijajnen) R.E. Norris, Hori & Chihara (Chlorophyta) and Phaeodactylum tricornutum Bohlin (Bacillariophyta) cultures of Black Sea microalgae using TsV-S1 and PtV-S18 algal virus strains isolated from the Black Sea ecosystem. The study assesses the effects of light intensity and the initial abundance of microalgae cells on the onset of their infection by viruses and the decline in their abundance. As early as on the second or third day, the cells changed their shape and increased in volume in the cultures infected by viruses. At this time, a decrease was observed in chlorophyll a red autofluorescence, variable fluorescence per cell, and photochemical efficiency of photosystem 2. In the studied cultures, a reduction in cell abundance due to viral lysis was noted 1 to 2 days later. The threshold cell abundance at which this process was observed was independent of light conditions and amounted to 3 × 105 cells/mL for T. viridis and 18 × 105 cells/mL for Ph. tricornutum. The complete lysis of algae cells was detected by the end of the fourth to sixth day. In the dark, the effect of viruses on microalgae was insignificant.