Tolerance of microalgae Dunaliella salina and Phaeodactylum tricornutum to various concentrations of selenium in the medium

Cell number dynamics and growth rate of microalgaeDunaliella salina(Chlorophyta) andPhaeodactylum tricornutum(Bacillariophyta) are considered in dependence on selenium concentration in the medium. The concentrations 0.01, 0.10, and 0,50 mg/l were tested. Onetime addition of selenium did not influence on the cell number and morphology ofD. salina. Under repeatable addition of selenium (every 2 days), reliable differences in the cells number were detected for the concentration 0.10 mg/l only, but the concentrations 0.01 and 0.50 mg/l did not make any effect on the cells different from the control. Under frequent repeatable addition of selenium (every day), the concentration 0.50 mg/l caused a visible decreasing of the cell number in compare with the control sample — after 6 days the cells started to decay, settled to the flask bottom and aggregated, the suspension color turned to yellowish. Reaction of diatomPhaeodactylum tricornurumwas more complicated. Its cell number increased signifcantly against the control under both one-time addition of selenium in the concentration of 0.10 and 0.50 mg/l or the repeatable addition in every 2 days in the concentration 0.01 and 0.10 mg/l. But more frequent (every day) addition of selenium in the concentration 0.50 mg/l caused inhibition of the cells growth and decreasing of their number against the control sample — after 4 days the cells adhesion to the flask bottom was detected, apparently because of their metabolism alteration.