Cho Kichul, Wencheng Li, Takeshita Satoshi, Seo Jung-Kil, Chung Young-Ho, Kim Daekyung, Oda Tatsuya
Geum River Environment Research Center, National Institute of Environmental Research, Jiyong street, Okcheon gun, Chungcheongbuk do 29027, Republic of Korea.
Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
Aquat Toxicol. 2017 Aug;189:209-215. doi: 10.1016/j.aquatox.2017.06.016. Epub 2017 Jun 19.
Heterocapsa circularisquama, a harmful dinoflagellate, has multiple haemolytic toxins that are considered to be involved in the toxic mechanism against shellfish and certain species of zooplankton. To evaluate the further nature of the toxins of H. circularisquama, we investigated its effects on several species of bacteria. By colony formation assay, we found that H. circularisquama had antibacterial activity toward the marine bacterium Vibrio alginolyticus in a cell density-dependent manner. When the inoculated bacterial cells were co-cultured with H. circularisquama under dinoflagellate cell culture conditions, the bacterial growth was significantly suppressed, whereas the number of live bacterial cells increased when cultured in the medium alone. Since the cell-free culture supernatant and the ruptured dinoflagellate cell suspension showed no toxic effects on V. alginolyticus, it is speculated that direct cell-to-cell contact mediated by the live dinoflagellate cells may be the major toxic mechanism. The decrease in bactericidal activity of theca-removed dinoflagellate cells may further support this speculation. H. circularisquama also showed bactericidal activities towards Escherichia coli and Staphylococcus aureus. In the dinoflagellate/bacteria co-culture system, the number of live bacterial cells declined with increasing incubation time. Light-dependent antibacterial activity of the ruptured dinoflagellate cells against S. aureus was observed, whereas no such activity was detected against E. coli. These results suggest that intracellular photosensitising bactericidal toxins, which were previously found to be porphyrin derivatives, may have specificity towards gram-positive bacteria. Based on these results together with previous studies, it is obvious that H. circularisquama possesses antibacterial activity, which may be mediated through toxins located on its cell surface. It is likely that such toxins play a role in the defence mechanism against predators and infectious bacteria. Although the exact biological significance of intracellular photosensitising toxins is still unclear, such toxins may have potential to be developed as novel photo-controllable antibiotics.
圆形异帽藻是一种有害的甲藻，它含有多种溶血毒素，这些毒素被认为参与了对贝类和某些浮游动物种类的毒性作用机制。为了进一步评估圆形异帽藻毒素的性质，我们研究了它对几种细菌的影响。通过菌落形成试验，我们发现圆形异帽藻对海洋细菌溶藻弧菌具有细胞密度依赖性的抗菌活性。当接种的细菌细胞在甲藻细胞培养条件下与圆形异帽藻共培养时，细菌生长受到显著抑制，而单独在培养基中培养时活细菌细胞数量增加。由于无细胞培养上清液和破裂的甲藻细胞悬液对溶藻弧菌没有毒性作用，推测活甲藻细胞介导的直接细胞间接触可能是主要的毒性机制。去除细胞壁的甲藻细胞杀菌活性的降低可能进一步支持这一推测。圆形异帽藻对大肠杆菌和金黄色葡萄球菌也表现出杀菌活性。在甲藻/细菌共培养系统中，活细菌细胞数量随着培养时间的增加而减少。观察到破裂的甲藻细胞对金黄色葡萄球菌具有光依赖性抗菌活性，而对大肠杆菌未检测到这种活性。这些结果表明，先前发现的细胞内光敏杀菌毒素可能是卟啉衍生物，对革兰氏阳性细菌具有特异性。基于这些结果以及先前的研究，很明显圆形异帽藻具有抗菌活性，这可能是通过其细胞表面的毒素介导的。这种毒素可能在抵御捕食者和感染性细菌的防御机制中发挥作用。尽管细胞内光敏毒素的确切生物学意义仍不清楚，但这种毒素可能有潜力被开发为新型光控抗生素。
