EFFECTS OF SULFATE ON SELENATE UPTAKE AND TOXICITY IN THE GREEN-ALGA SELENASTRUM-CAPRICORNUTUM

Sulfate and selenate compete for active transport across cell membrane s via a common permease, suggesting that a significant interaction may exist between uptake of the two ions. The effect of sulfate on selena te uptake and toxicity in Selenastrum capricornutum was investigated u sing two sulfate levels (3.3 and 33 mg/L S, as SO4) and two selenate l evels (10 and 100 mu g/L Se, as SeO4). This provided four treatments: one with S:Se molar ratio of 75, two with molar ratios of 750, and one with a molar ratio of 7,500. Selenium uptake and toxicity analyses de monstrated antagonism between the two anions. Increasing sulfate resul ted in significantly reduced selenate uptake and increased algal growt h. There was a significant difference in selenate uptake between the t wo treatments with the same S:Se molar ratio suggesting different rela tive permease affinities for each of the ions at different substrate l evels (i.e., above and below permease saturation levels) and/or the pr esence of two different permease systems. The environmental significan ce of sulfate and selenate antagonism is discussed.