Algicidal activity and mechanism of novel Bacillamide a derivative against red tide algae Skeletonema costatum and Prorocentrum minimum

Frequent red tide outbreaks pose a serious threat to biodiversity and the safety of aquatic ecosystems. Bacillamides showed algicidal activity against algae. However, the low natural concentrations and their structural complexity hinder development of these molecules. Inspired by the natrual algicide Bacillamide A, a series of thiourea derivatives were synthesized. Bacillamide A derivative (3B) showed excellent algicidal activity against S. costatum (EC₅₀ = 0.52 μg/mL) and P. minimum (EC₅₀ = 2.99 μg/mL), respectively. In addition, it has low toxicity to mammals and is less toxic than copper sulfate. 3B treatment resulted in loss of algal cell integrity. It also decreased the Chlorophyll a content and Fv/fm of algal cells, while increasing the levels of malondialdehyde content, superoxide dismutase, and reactive oxygen. 3B also induced expression of the photosynthetic genes, including psaB, psbB, as well as the antioxidant genes SOD2 and CAT. This study demonstrates that Bacillamide A derivatives could provide a safer alternative for red tide algal management.