Cyanobacteria--a potential source of new biologically active substances.

Hydrophilic and lipophilic extracts of twelve cyanobacterial strains, isolated from fresh and brackish water, and two waterblooms, collected during the summer from the Baltic Sea, were investigated for their antibiotic activities against seven microorganisms. No inhibitory effects were found against the three Gram-negative bacteria Escherichia coli, Proteus mirabilis and Serratia marcescens and the yeast Candida maltosa. Of all cyanobacterial samples, extracts from seven species inhibited the growth of at least one of the Gram-positive bacteria Micrococcus flavus, Staphylococcus aureus and Bacillus subtilis. M. flavus proved to be the most sensitive bacterium in the agar diffusion test system. In particular, the hexane and dichlormethane extracts showed antimicrobial effects. But only one water extract, prepared from material of a natural waterbloom, was found to be active.