Microalgal Microscale Model for Microalgal Growth Inhibition Evaluation of Marine Natural Products

Marine organisms especially sessile invertebrates, such as soft corals, gorgonians and sponges, can survive in the competitive environment mainly relying on their second metabolites with chemoecological effects including allelopathy and algal growth inhibition. It is well known that the microscale models are urgently needed in marine chemoecology assessment to evaluate the algal growth inhibition activity of trace quantity natural products. In this work, a microalgal growth inhibition model was established for microalgal inhibition evaluation of marine natural products with 96-well microplate by automatic fluorescence observation using microplate reader. Subsequently, this model was applied to bioassay-guided isolation and preliminary bioactivity screening of the secondary metabolites from soft corals, gorgonians, sponges and their symbiotic microbes collected from the South China Sea. As a result, fifteen compounds (1‒15) were found to exhibit microalgal growth inhibition activities against at least one of marine microalgae, Karenia mikimotoi, Isochrysis galbana, and Heterosigma akashiwo. Specifically, altersolanol C (13) demonstrated potent activity against K. mikimotoi with the 96h-EC₅₀ value of 1.16 µg/mL, more than four times stronger than that of the positive control K₂Cr₂O₇. It was suggested that the microalgal growth inhibition microscale model is suitable for bioassay-guided isolation and preliminary bioactivity screening of marine natural products.