The relationship between algicidal bacteria and harmful-algal-bloom-forming dinoflagellates is understudied and their action modes are largely uncharacterized. In this study, an algicidal bacterium (FDHY-03) was isolated from a bloom of Prorocentrum donghaiense and the characteristics of its action against P. donghaiense was investigated at physiological, molecular, biochemical and cytological levels. 16S rDNA sequence analysis placed this strain in the genus of Alteromonas in the subclass of γ-proteobacteria. Algicidal activity was detected in the bacterial filtrate, suggesting a secreted algicidal principle from this bacterium. Strain FDHY-03 showed algicidal activity on a broad range of HAB-forming species, but the greatest effect was found on P. donghaiense, which showed 91.7% mortality in 24 h of challenge. Scanning electron microscopic analysis indicated that the megacytic growth zone of P. donghaiense cells was the major target of the algicidal action of FDHY-03. When treated with FDHY-03 culture filtrate, P. donghaiense cell wall polysaccharides decreased steadily, suggesting that the algicidal activity occurred through the digestion of cell wall polysaccharides. To verify this proposition, the expression profile of beta-glucosidase gene in FDHY-03 cultures with or without P. donghaiense cell addition was investigated using reverse-transcription quantitative PCR. The gene expression level increased in the presence of P. donghaiense cells, indicative of beta-glucosidase induction by P. donghaiense and the enzyme’s role in this dinoflagellate’s demise. This study has isolated a new bacterial strain with a strong algicidal capability, documented its action mode and biochemical mechanism, providing a potential source of bacterial agent to control P. donghaiense blooms.

杀藻细菌与有害藻华形成的鞭毛藻之间的关系尚未得到充分研究，其作用方式在很大程度上尚未阐明。在这项研究中，从东海原小球藻的花样中分离出了一种杀藻细菌（FDHY-03），并在生理，分子，生化和细胞学水平上研究了其对东海假单胞菌的作用特性。16S rDNA序列分析将该菌株置于γ-变形杆菌亚类的Alteromonas属中。在细菌滤液中检测到杀藻活性，表明该细菌分泌了杀藻原理。FDHY-03菌株对多种形成HAB的菌种均具有杀藻活性，但对P. donghaiense，在攻击后24小时内死亡率为91.7％。扫描电镜分析表明，东海假单胞菌细胞的大细胞生长区是FDHY-03杀藻作用的主要靶标。当与FDHY-03培养物滤液进行处理，东海原细胞壁多糖稳步下降，提示通过细胞壁多糖的消化发生杀藻活性。为了验证这一主张，使用逆转录定量PCR研究了添加或不添加东海假单胞菌的FDHY-03培养物中β-葡萄糖苷酶基因的表达谱。东海假单胞菌存在下基因表达水平升高。细胞，表明东海疟原虫诱导了β-葡萄糖苷酶的存在，以及该酶在该鞭毛鞭毛藻灭亡中的作用。这项研究分离出了具有强杀藻能力的新细菌菌株，并记录了其作用模式和生化机理，为控制东海疫霉菌的开花提供了潜在的细菌来源。