The Establishment Of A Miniaturized Microalgal Growth-inhibition Bioassay And Its Application On Effect Of Chemical Ecology

Marine microalgae as the dominant primary producers,play an essential role in the marine ecosystems. Microalgae are the first and requisite targets in the study of chemical ecology because they are more sensitive than fish and crustaceans to test chemical.A small-scale microplate microalgal growth-inhibition test was established using Heterosigma akashiwo, Isochrysis galbana. Karenia mikimotoi, Platymonas helgolandica var. tsingtaoensis, together with fluorescence measurement of quantifying algal growth. This test model has good feasibility, accuracy, stability and reproducibility. Comparing with the standard flask assay, microbiotests cost effectively, require low sample volumes, allow large numbers of samples to be tested, and generate low volumes of waste with time and space saving contributed to estimatethe ecology character of chemcals. This miniaturized microalgal growth-inhibition bioassay was successfully applied to detect the growth-inhibitory activity on microalgae of marine natural products. The modal was contributed to guide the isolation of active compound, screen compounds and analysis the structure-activity relationship. The results proved that microbiotests showed good reliability and practicality. 116 compounds isolated from 12 species were screened by microalgal growth-inhibition bioassay.It was found that different algal species had variable sensitivity to same compounds. Bisabolane sesquiterpenoid showed stronger inhibitory activity to Heterosigma akashiwo than Isochrysis galbana, while scalarane sesterterpene displayed opposite activity.Cembrene diterpene manifested selective inhibitory activity to Karenia mikimotoi. Sterides displayed strongest inhibitory activity to Isochrysis galbana among four microalgae. Polyketide compounds had common algal inhibitory activity to the four microalgae.From structure-activity analysis, it was found compounds of different structural types showed a clear relationship between structure and activity. The inhibitory activity of sterides were related to the number of hydroxyl. The bigger the number of phenolic hydroxyl group of bisabolane sesquiterpenoid, the stronger of its algal growth-inhibitory activity.