A fungus, Aureobasidium pullulans, was isolated from marine biofilm and identified. A bioassay-guided fractionation procedure was developed to isolate and purify antifouling compounds from A. pullulans HN. The procedure was: fermentation broth—aeration and addition of sodium thiosulfate–graduated pH and liquid–liquid extraction—SPE purification—GC–MS analysis. Firstly, the fermentation broth was tested for its toxicity. Then it was treated with aeration and addition of sodium thiosulfate, and its toxicity was almost not changed. Lastly, antifouling compounds were extracted at different pH, the extract had high toxicity at pH 2 but almost no toxicity at pH 10, which suggested the toxicants should be fatty acids. The EC50 of the extract against Skeletonema costatum was 90.9μgml−1, and its LC50 against Balanus amphitrete larvae was 22.2μgml−1. After purified by HLB SPE column, the EC50 of the extract against S. costatum was 49.4μgml−1. The myristic and palmitic acids were found as the main toxicants by GC–MS.

This study evaluates the inhibitory effect of a yeast strain, Aureobasidium pullulans KKUY0701, isolated from decayed cyanobacterial bloom against harmful cyanobacterium Microcystis aeruginosa and determines the ability of this strain to remove microcystin (MC) toxin from the water. The antialgal activity of this yeast strain was assayed by co-cultivation with M. aeruginosa, diatom, and green algal species. The MC adsorption experiment was conducted in the presence of living and heat-inactivated yeast cells. Both yeast cells and filtrates caused a rapid reduction in the growth of M. aeruginosa, with complete death and cell lysis occurring after 3 days. The yeast strain did not exhibit any inhibitory effect on either green algae or diatoms. Both living and heat-inactivated yeast cells were capable of adsorption of MC on their surfaces. Inactivated yeast exhibited higher adsorption capacity and lower intensity than living yeast for the adsorption of MC toxin. The results of this study suggest that this yeast strain could be employed to selectively reduce cyanobacterial blooms in freshwaters. Moreover, the application of heat-inactivated yeast’s biomass for toxin adsorption gives new possibilities in drinking water treatment plants.