Characterization of cell death in harmful Karenia mikimotoi under algicidal activity of Marinobacter sp. O-7

Abstract

Use of algicidal bacteria, which has the advantage of both safety and efficiency, has gradually become a significant strategy to handle the environmental problem of Harmful Algal Blooms (HABs). A strain of bacterium with excellent algicidal activity of 95.6% and identified as Marinobacter sp. (O-7) was isolated from seawater. The results demonstrated that strain O-7 can secrete active substances, which can pose a fatal threat to harmful Karenia mikimotoi. The morphology of K. mikimotoi cells changed over time. The physiological responses of algal cells after exposure to strain O-7 algicidal compounds were as follows: photosynthetic pigments (chlorophyll a and carotenoid) levels of the algal cells decreased significantly as did the photosynthetic efficiency and performance index, while reactive oxygen species levels substantially increased under the stress of 3% dose of O-7 for 4 h of treatment. Concurrently, the intracellular antioxidant enzymes system (superoxide dismutase, catalase, glutathione peroxidase) and non-enzymes system (glutathione, oxidized glutathione, ascorbic acid and dehydroascorbic acid) showed up-regulation. The content of malondialdehyde amplified with increase in concentration, indicating lipid peroxidation of algal cells. Collectively, our results demonstrated that the secretion of O-7 could act as an effective algicide for the control of harmful algae and offered clues to understanding the death mechanism of indirect processing of bacterial secretion against microalgae.