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-Nf) a nd a Cr-tolerant strain (S2-T) of Scenedesmus acutus were tested for t heir capacity of reducing Cr toxicity to the algae and the filter-feed er Daphnia magna. The filtrates were supplemented either with 1 mg/l C r(VI) and used as culture media for the wild type of S. acutus, or wit h 14 mu g/l Cr(VI) and used as media to breed daphnids. In the experim ents with algae both filtrates partially counteracted the growth-inhib iting activity of chromium, but the effect of the filtrate of S2-T was much greater. In the experiments with daphnids the algal filtrates ha d toxic effects, causing reduction of growth, fecundity and life-span. The same effects were obtained with the filtrates deprived of the org anic matter. The filtrates of S2-T differed from those of S2-N because of their higher content in carbohydrates and because the electrophore tic pattern of the proteins extruded by S2-T showed three peaks not pr esent in the proteins extruded by S2-N.