Antibiotic activity of new cyanobacterial isolates from Australia and Asiaagainst green algae and cyanobacteria

One hundred and ninety-eight cyanobacterial strains, newly isolated mainly from samples collected from diverse habitats in Australia, Indonesia, Nepal , Thailand and Vietnam, were screened from their antibiotic activity agains t green algal species of the genera Coelastrum, Scenedesmus and Monoraphidi um, We report the discovery of ten strains of Fischerella, seven of Nostoc and three of Calothrix that produce antialgal compounds with a broad activi ty spectrum. Some of these bioactive cyanobacteria inhibited all three alga e, whereas others inhibited only two, and some only one. In addition, the 2 0 active strains were tested against other selected cyanobacteria, includin g Anabaena doliolum which grows well both photoautotrophically in light and heterotrophically in darkness, and three toxic species, Microcytis aerugin osa, Anabaena circinalis and Nodularia spumigena, which are problems in Aus tralia and other parts of the world. At least one Fischerella strain bad bi oactivity directed against photosynthetic electron transport of algal chlor oplasts, whereas others had no effect on photosynthesis. In most cases the growth inhibitory effects were also tested in the presence of a proteinase. The results are discussed in the light of the possible nature of the chemi cal inhibition and also in relationship to competition and allelopathy in a lgal populations.