The algicidal activity and characteristics of the novel marine algicidal bacterium Paracoccus sp. Y42 against a harmful algal bloom causing dinoflagellate, Prorocentrum donghaiense

Prorocentrum donghaiense blooms frequently occur in the Yangtze River Estuary and the adjacent East China Sea. These blooms have damaged marine ecosystems and caused enormous economic losses over the past two decades. Thus, highly efficient, low-cost, ecofriendly approaches must be developed to control P. donghaiense blooms. In this study, a bacterial strain (Y42) was identified as Paracoccus sp. and used to lyse P. donghaiense . The supernatant of the Y42 culture was able to lyse P. donghaiense, and the algicidal activity of this Y42 supernatant was stable under different temperatures and durations of light exposure and over a wide pH range. In addition to P. donghaiense , Y42 showed high algicidal activity against Alexandrium minutum, Scrippsiella trochoidea, and Skeletonema costatum, suggesting that it primarily targets Pyrrophyta. To clarify the algicidal effect of Y42, we assessed algal lysis and detected the chlorophyll a content, photosynthetic activity, and malondialdehyde content of P. donghaiense after exposure to the Y42 supernatant. Scanning and transmission electron microscopy analyses showed that the Y42 supernatant disrupted membrane integrity and caused algal cell breakage at the megacytic zone. Photosynthetic pigment loss and significant declines in both photosynthetic efficiency and electron transport rate indicated that the Y42 supernatant damaged the photosynthetic system of P. donghaiense . Malondialdehyde overproduction indicated that the Y42 supernatant caused lipid peroxidation and oxidative damage to membrane systems in the algal cell, ultimately leading to death. The findings of this study reveal the potential of Y42 to remove algal cells from P. donghaiense blooms. Importance P. donghaiense is one of the most common dinoflagellate species that form harmful algal blooms, which frequently cause serious ecological pollution and pose health hazards to humans and other animals. Hence, screening for bacteria with high algicidal activity against P. donghaiense and studying their algicidal processes and characteristics will contribute to an understanding of their algicidal effects and provide a theoretical basis for preventing algal blooms and reducing their harm to the environment. This study reports the algicidal activity and characteristics of Paracoccus against P. donghaiense . The stability of the algicidal activity of Paracoccus in different environments (including different temperature, pH and sunlight conditions) indicates its potential for use in the control of P. donghaiense blooms.