Effects of algicidal bacterium BS03 (Microbulbifer sp.) on the growth and antioxidant systems of Alexandrium tamarense

Abstract:

Abstract:［Objective］We studied the algicidal mechanism of extracellular substances of algicidal bacteria strain BS03 (Microbulbifer sp.) on photosynthetic characteristics，antioxident enzyme system and cysteine-dependent aspartate specific protease-3 (Caspase-3) of Alexandrium tamarense． ［Methods］ We tested photosynthetic pigments，chlorophyll fluorescence efficiency，antioxidant systems and caspase-3 activity in the algae cells treated with 0.5%，1.0%，1.5% and 2.0% BS03 cell-free filtrate after 12，24，36 and 48 h.［Results ］(1) The chlorophyll-a and chlorophyll fluorescence efficiency Fv/Fm decreased with the increase of BS03 cell-free filtrate and treatment time． Carotenoids contents of A． tamarense cells treated with low BS03 (0.5% and 1.0%) cell-free filtrate were higher than the control．(2) Antioxident enzyme activities varied as treatment time and concentration． Malodialdehyde (MDA) contents increased significantly with BS03 cell-free filtrate treatment．(3) Caspase-3 protease activities of algal cells increased by BS03 cellfree filtrate.[Conclusion] BS03 inhibited the photosynthesis whereas enhanced the lipid peroxidation of the cellular membrane of Alexandrium tamarense，indicating its algicidal activity．

Key words:Keywords: Alexandrium tamarense，algicidal bacteria，photosynthetic pigment，antioxidant defense system