Effect of algicidal compound Nω-acetylhistamine on physiological response and algal toxins in Heterosigma akashiwo.

The toxic alga Heterosigma akashiwo (Raphidophyceae) is known to form harmful algal blooms (HABs), which can have serious negative effects on the aquatic ecosystem and human life. Previous study has shown that Nω-acetylhistamine (N-AcH), an algicidal compound secreted by algicidal bacteria Bacillus sp. Strain B1, can inhibit the growth of H. akashiwo. In this study, the algicidal mechanism of N-AcH against H. akashiwo was explored, and the changes of toxicity of H. akashiwo treated with N-AcH were investigated. The algal inhibition rate was calculated by the optical density method, and the results showed that the growth inhibition rate of H. akashiwo was about 90% when treated in the medium with 40 μg/mL N-AcH at 96 h. After 72 h treatment, transmission electron microscopy (TEM) showed that the microstructure of H. akashiwo cell was seriously damaged at this concentration. The content of Chlorophyll a and Chlorophyll b decreased while malonaldehyde levels increased, and superoxide dismutase activity first increased and then decreased as well as soluble protein content. GC-MS revealed that the type and content of fatty acids cut down after 48 h and 96 h treatment. Hemolytic test, MTT assay, and micronucleus test all demonstrated the decrease in the toxicity of H. akashiwo treated with 40 μg/mL N-AcH. In brief, N-AcH mainly kills H. akashiwo cell through oxidative stress and can also reduce its toxicity, so it is a promising algicide with the dual functions of killing algae and inhibiting algal toxic effects.