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Harmful algal blooms: mechanisms, monitoring, and prevention in a rapidly changing world
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The effective algicidal bacterium Microbulbifer maritimus TF-17 triggered Phaeocystis globosa autophagy dominated by membrane destruction
P-B1-19-S
Zhu Xiaoying* , School of life sciences, Xiamen University
Presenter Email: zxynwsuaf@126.com |
| Phaeocystis globosais one of the disruptive harmful algal blooms (HABs) algae strains in South China. It can form capsules to block fish and can cause hemolytic toxins to pollute the environment. We have isolated a bacteria strain from the mangrove wetland in Zhangzhou, Fujian Province, which can kill 90% of algae cells in 72 hours. The effective algicidal bacterium was identified as Microbulbifer maritimus TF-17 by 16S rDNA sequence blasting. The results of GC-MS indicated that the active substance of Microbulbifer maritimus TF-17 is cyclic dipeptide, with temperature and acid-base stability. In order to utilize the algicide material efficiently, we conducted a preliminary study on the mechanism of algae killing. It was found that the content of malondialdehyde (MDA) in P. globosa cells increased after adding bacterial sterile supernatant for only 6 hours, while the levels of NO and H2O2 in algae cells increased significantly in 12 hours treatment. At the same time, the activities of enzymes related to oxygen free radical scavenging (POD, CAT, etc.) are enhanced. This indicates that membrane peroxidation occurs first and the inner membrane of the cell is initially attacked. At the same time, the morphological changes of algal cells were also significant. The flagella of algal cells break off, and the cells deform, producing round bubbles. Compared with healthy cells, algal cell organelles (chloroplasts, mitochondria) are sparse in structure, without obvious membranes, and eventually disappear. Algae cell nuclear membrane disappeared, chromatin marginalized, nucleoli gradually disappeared. A large number of autophagosome structures are produced invivo, and eventually the cells become vacuolated to death. In addition, we also found that although the TEM results showed severe nuclear damage, no obvious DNA Ladder was formed, possibly because the algal nuclei were affected but did not break into small fragments. It was concluded that triggered by Microbulbifer maritimus TF-17, the cytoplasmic membrane of globular brown cystis was first damaged, a large amount of NO and H2O2 was produced in the cell, and the antioxidant system was also activated, but still could not prevent cell death. This form of death begins with the destruction of internal organelles by autophagy. Our study suggested that under the stress of Microbulbifer maritimus TF-17, P. globosa cell death is autophagy as similar as in plant which was starting with membrane damaged. |
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