Allelopathic activity of the Synechococcus sp. (Cyanobacteria, Chroococcales) on selected cyanobacteria species

Picocyanobacterium Synechococcus sp. is very important but still poorly understood component of marine and freshwater ecosystems. In this study, the effect of single and multiple addition of cell-free filtrate obtained from Synechococcus sp. on selected cyanobacteria Synechocystis sp., Geitlerinema amphibium, Nodularia spumigena and Nostoc sp. was investigated. The species present in this work are groups of aquatic phototrophs known to co-occur in the Baltic Sea. The study showed that the picocyanobacterial cell-free filtrate inhibit the growth and changed the cell morphology of filamentous cyanobacteria G. amphibium, N. spumigena and Nostoc sp. It was shown that the addition of cell-free filtrate caused a decline of pigmentation and cell lysis of G. amphibium, N. spumigena and Nostoc sp. compared to the control culture. In addition, it was observed that the filtrate obtained from Synechococcus sp. did not affect the Synechocystis sp. It was found that the filtrate obtained from picocyanobacterium had the strongest effect on growth of G. amphibium, therefore for this cyanobacteria performed additional experiments to showed whether the filtrate affected also photosynthetic pigments, chlorophyll fluorescence and photosynthesis. The study proved that the picocyanobacterial allelopathic compounds reduce the efficiency of photosynthesis, which results in the inhibition of growth of target organisms. This way of interaction may explain the formation of almost monospecific cyanobacterial blooms in many aquatic ecosystems, including in the Baltic Sea.