Algicidal Mechanism Of Biosurfactant Against Heterosigma Akashiwo

Algal bloom is a rapid increase or accumulation in the population of phytoplankton,bacteria or protozoa in marine water systems.Blooms which can produce toxins and threaten other organism in water body are called harmful algal blooms(HABs).The bloom of Heterosigma akashiwo,which has occurred frequently in China's sea area,can cause great harm to marine environment and fishery aquaculture.Looking for environment friendly methods to control HABs have gained increasing attention.Biosurfactants are amphiphilic compounds which can emulsify,enhance the solubility and decrease the surface tension of liquid.In contrast to surfactants,biosurfactant also has the advantages of biodegradation,no secondary pollution and environment friendly.Biosurfactants have been widely used in bioremediation of contaminated environment.In order to investigate the potential of biosurfactants in the control of HABs,the algicidal biosurfactant BA01 was chosen for further analysis.In this study,we analyzed the physicochemical property of BA01 and explored the algicidal mechanism of BA01 on HABs species H.akashiwo.The main results are summarized as follows:(1)Chemical analysis of BA01 indicated that it is a nonionic surfactants composed of 6.2%total protein and 14.1%sugar;The surface tension and algicidal activity of BA01 was stable after being exposed to different temperature,salinity and pH.(2)BA01 showed obvious inhibition effects against Pyrrophyta,Bacillariophyta and Xanthophyta,however,it had almost no effect on Chlorophyta and Cyanobacteria,indicating that BA01 is specific and selective.After H.akashiwo cells were exposed to BA01 for 48 h,low concentration of BA01(2.5 ?g/mL)showed the algicidal rate as 24.49%,while high concentration group(15 ?g/mL)inhibited 97.76%algal cells growth and the median lethal concentration(LC50)of BA01 on H.akashiwo was 5.89?g/mL.(3)The results indicated that semi-lethal concentration had little influence on algal morphology.The PI and Annexin V staining assay determined that cells and organelle structure remain intact with slightly damaged membrane.Based on this fact,ROS levels sustained high,that stimulated antioxidant to remain active to scavenge ROS.The inhibition of photosynthesis appeared initially,photosynthetic efficiency gradually recovered after the cells repaired the damage.The content of photosynthetic pigments such as chlorophyll and carotenoids decreased to 50%of the control group.(4)The algae exposed to lethal concentration BA01 had broken membrane and its organelles failed to work properly.As the cell contents flowed out,the anti-oxidation system failed to work,that means ROS cannot be cleared.The accumulation of ROS caused lipid peroxidation and intracellular MDA content increased significantly.Photosynthetic system of H.akashiwo were damaged and it was hard to repaired due to the stress made by BA01,so the photosynthetic efficiency continued to decline.The photosynthetic pigments content was only 15%of the control group.