Exudates from the wild type and a CR-tolerant strain of Scenedesmus acutus influence differently CR(VI) toxicity to algae

Culture filtrates containing the exudates from the wild type (S2-N) and a Cr-tolerant strain (S2-T) of Scenedesmus acutus were tested for their capacity of reducing Cr toxicity to the algae and the filter-feeder Daphnia magna. The filtrates were supplemented either with 1 mg/1 Cr(VI) and used as culture media for the wild type of S. acutus, or with 14 μg/t Cr(VI) and used as media to breed daphnids. In the experiments with algae both filtrates partially counteracted the growth-inhibiting activity of chromium, but the effect of the filtrate of S2-T was much greater. In the experiments with daphnids the algal filtrates had toxic effects, causing reduction of growth, fecundity and life-span. The same effects were obtained with the filtrates deprived of the organic matter. The filtrates of S2-T differed from those of S2-N because of their higher content in carbohydrates and because the electrophoretic pattern of the proteins extruded by S2-T showed three peaks not present in the proteins extruded by S2-N.