Huajun

Zhang, Xinli An, Yanyan Zhou, Bangzhou Zhang, Su Zhang, Dong Li, Zhangran

Chen,Yi Li, Shijie Bai, Jinglin Lv, Wei Zheng, Yun Tian, Tianling Zheng,PLOS

ONE, 2013,8(5): e63018

Harmful algal blooms occur all over the

world, destroying aquatic ecosystems and threatening other organisms. The

culture supernatant of the marine algicidal actinomycete BS01 was able to lysis

dinoflagellate Alexandrium tamarense ATGD98-006. Physiological and biochemical

responses to oxidative stress in A. tamarense were investigated to elucidate

the mechanism involved in BS01 inhibition of algal growth. Transmission

electron microscope analysis revealed that there were some chloroplast

abnormalities in response to BS01 supernatant. The decrease in cellular-soluble

protein content suggested that cell growth was greatly inhibited at high

concentration of BS01 supernatant. The increase in the levels of reactive

oxygen species (ROS) and malondialdehyde contents following exposure to BS01

supernatant indicated that algal cells suffered from oxidative damage. The

content of pigment was significantly decreased after 12 h treatment, which

indicated that the accumulation of ROS destroyed pigment synthesis. Moreover,

the decrease of Fv/Fm ratio suggested that in the photosynthetic system, the

dominant sites producing ROS were destroyed by the supernatant of the BS01

culture. The activities of the antioxidant enzymes including superoxide

dismutase and peroxidase increased in a short time and decreased slightly with

increasing exposure time. A real-time PCR assay showed changes in the transcript

abundances of two photosynthetic genes, psbA and psbD. The results showed that

BS01 supernatant reduced the expression of the psbA gene after 2 h exposure,

but the expression of the psbD gene was increased at concentrations of 1.0 and

1.5%. Our results demonstrated that the expression of the psbA gene was

inhibited by the BS01 supernatant, which might block the electron transport

chain, significantly enhancing ROS level and excess activity of the antioxidant

system. The accumulation of ROS destoryed pigment synthesis and membrane

integrity, and inhibited or ultimately killed the algal cells.

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