Effects of toxic cyanobacterium Microcystis aeruginosa on the morphology of green alga Chlorella vulgaris

In eutrophic freshwater lakes, cyanobacteria and green algae are in succession due to abiotic factors. Allelochemical interaction also exists. In this study, we indicated that filtrates of Microcystis aeruginosa can influence the growth rate and photosynthetic pigments of the target alga named Chlorella vulgaris. We also determined the morphological appearance and colony formation of green alga C. vulgaris that were induced by chemicals associated with a competitor cyanobacterium named M. aeruginosa. However, microcystins (MCs) were not the active substances in this study. The morphology changes and growth of C. vulgaris affected by M. aeruginosa filtrates were dependent on the initial cultivation density of the target algae and the cultivation phase of M. aeruginosa. We also assumed that the morphology changes were defensive strategies utilised by C. vulgaris to resist M. aeruginosa. The temporary stress of M. aeruginosa was favourable to the growth of C. vulgaris. By contrast, the continuous induction of colony formation by M. aeruginosa in the field inhibited the growth of C. vulgaris. The present results provided new insights into the interaction between algae and theoretical basis for algae succession in the field.