Chemically mediated interactions between Microcystis and Planktothrix: impact on their growth, morphology and metabolic profiles

Freshwater cyanobacteria are known for their ability to produce bioactive compounds, some of which have been described as allelochemicals. Using a combined approach of co-cultures and analyses of metabolic profiles, we investigated chemically mediated interactions between two cyanobacterial strains, Microcystis aeruginosaPCC7806 and Planktothrixagardhii PCC7805. More precisely, we evaluated changes in growth, morphology and metabolite production and release by both interacting species. Co-culture of Microcystiswith Planktothrixresulted in a reduction of the growth of Planktothrixtogether with a decrease of its trichomesize and alterations in the morphology of its cells. The production of intracellular compounds by Planktothrixshowed a slight decrease between mono and co-culture conditions. Concerning Microcystis, the number of intracellular compounds was higher under co-culture condition than under monoculture. Overall, Microcystisproduced a lower number of intracellular compounds under monoculturethan Planktothrix, and a higher number of intracellular compounds than Planktothrixunder co-culture condition. Our investigation did not allow us to identify specifically the compounds causing the observed physiological and morphological changes of Planktothrixcells. However, altogether, these results suggest that co-culture induces specific compounds as a response by Microcystisto the presence of Planktothrix. Further studies should be undertaken for identification of such potential allelochemicals. This article is protected by copyright. All rights reserved.