Ifremer, PHYTOX, Rue de l'Île d'Yeu, 44311 Nantes Cedex 03, France.
Ifremer, PHYTOX, Rue de l'Île d'Yeu, 44311 Nantes Cedex 03, France.
Harmful Algae. 2023 Aug;127:102483. doi: 10.1016/j.hal.2023.102483. Epub 2023 Jul 30.
Many harmful algae are mixoplanktonic, i.e. they combine phototrophy and phagotrophy, and this ability may explain their ecological success, especially when environmental conditions are not optimal for autotrophic growth. In this study, laboratory experiments were conducted with the mixotrophic and ichthyotoxic haptophyte Prymnesium parvum (strain CCAP 946/6) to test the effects of phosphorus (P) sufficiency and deficiency on its growth rate, phagotrophic and lytic activities. P-deficient P. parvum cultures were grown without or with addition of P in the form of inorganic phosphorus (nutrients) and/or living algal prey (i.e. the cryptophyte Teleaulax amphioxeia). The ingestion rate of P. parvum and prey mortality rate were calculated using flow cytometry measurements based on pigment-derived-fluorescence to distinguish between prey, predators and digesting predators. The first aim of the study was to develop a method taking into account the rate of digestion, allowing the calculation of ingestion rates over a two-week period. Growth rates of P. parvum were higher in the treatments with live prey, irrespective of the concentration of inorganic P, and maximum growth rates were found when both inorganic and organic P in form of prey were added (0.79 ± 0.07 d). In addition, the mortality rate of T. amphioxeia induced by lytic compounds was 0.2 ± 0.02 d in the P-deficient treatment, while no mortality was observed under P-sufficiency in the present experiments. This study also revealed the mortality due to cell lysis exceeded that of prey ingestion. Therefore, additional experiments were conducted with lysed prey cells. When grown with debris from prey cells, the mean growth rate of P. parvum was similar to monocultures without additions of prey debris (0.30 ± 0.1 vs. 0.38 ± 0.03 d), suggesting that P. parvum is able to grow on prey debris, but not as fast as with live prey. These results provide the first quantitative evidence over two weeks of experiment that ingestion of organic P in the form of living prey and/or debris of prey plays an important role in P. parvum growth and may explain its ecological success in a nutrient-limited environments.
许多有害藻类是混养的，即它们结合了光合作用和吞噬作用，这种能力可能解释了它们的生态成功，特别是当环境条件不利于自养生长时。在这项研究中，用混养和鱼毒性的甲藻 P. parvum（CCAP 946/6 株）进行了实验室实验，以测试磷（P）充足和缺乏对其生长速度、吞噬和裂解活性的影响。在没有或添加无机磷（营养物）和/或活藻类猎物（即隐藻 T. amphioxeia）的形式的 P 缺乏 P. parvum 培养物中生长。使用流式细胞术测量基于色素衍生荧光来区分猎物、捕食者和正在消化的捕食者，计算 P. parvum 的摄食率和猎物死亡率。该研究的第一个目标是开发一种考虑到消化速度的方法，从而可以在两周的时间内计算摄食率。无论无机 P 的浓度如何，用活猎物处理的 P. parvum 生长率都较高，并且当以猎物的形式添加无机和有机 P 时，发现最大生长率（0.79±0.07 d）。此外，在本实验中，在 P 充足的情况下，缺乏 P 处理时 T. amphioxeia 诱导的裂解化合物死亡率为 0.2±0.02 d，而在 P 充足的情况下则没有观察到死亡率。本研究还揭示了细胞裂解引起的死亡率超过了猎物的摄食率。因此，进行了额外的实验，用裂解的猎物细胞进行实验。当用猎物细胞的碎片生长时，P. parvum 的平均生长率与没有添加猎物碎片的单培养物相似（0.30±0.1 与 0.38±0.03 d），这表明 P. parvum 能够在猎物碎片上生长，但不如活猎物快。这些结果提供了在两周的实验中首次定量证据，表明以活猎物和/或猎物碎片的形式摄入有机 P 在 P. parvum 生长中起着重要作用，并且可能解释了它在营养有限的环境中的生态成功。
