Bioactivity in free-living and symbiotic cyanobacteria of the genus Nostoc

Fifty cyanobacterial strains from different habitats (symbioses, soil, fresh and marine waters) belonging to the genus Nostoc were cultured and tested for bioactivity. Thirty-seven strains were isolated in our laboratory, the remaining were supplied by official culture collections. All the organisms were grown under controlled laboratory conditions. The biomasses were lyophilised and extracted with ethanol:water to obtain a hydrophilic extract and then with dichloromethane:isopropanol to obtain a lipophilic extract. Both crude extracts were tested for antifungal (against Penicillium expansum and Rhizoctonia solani) and antibacterial activity (against Agrobacterium vitis, Escherichia coli and Staphylococcus epidermidis), and for toxicity against Artemia salina nauplii. Twenty-four strains showed activity against at least one of the target organisms. Bioactivity was equally distributed between lipophilic and hydrophilic extracts, and was mostly directed against fungi (15 strains) and Artemia nauplii (12 strains); antibacterial activity was less frequent (8 strains). The presence of bioactivity was independent of the strain origin.