Antifungal activity of freshwater cyanobacteria

The antifungal activity of different freshwater cyanobacteria was determined in an agar diffusion bioassay using different species of Fusarium and other fungi as indicator organisms. Micromycetes which were used for the bioassay were Fusarium oxysporum, F moniliforme, F. gibbosum, F. culmorum, F. graminearum, F. avenaceum, F. sporotrichiella, F. solani, F javanicum, F. longipes, and also Bipolaris sorokiniana, Rhizoctonia solani, and Altemaria alternata. F. oxysporum proved to be the most sensitive fungus and was used for more detailed analyses. The strongest inhibitory activity of the cyanobacteria tested was found with Calothrix braunii, Tolypothrix tennis, Spirulina platensis, Oscillatoria sp., Hapalosiphon fontinalis, Gloeotrichia natans, and Lyngbya limnetica. It was shown that the major activity was retained in the cyanobacterial cells. Only very little activity was found in the culture filtrates suggesting that excretion of antifungal compounds by these cyanobacteria is of minor importance. The antifungal compounds of cyanobacteria could be extracted with 60% aq. methanol and were also found in extracts of dichloromethane.