15:45 〜 16:00
[AOS18-02] 金属系ナノ粒子汚染に対する海洋単細胞真核生物の生物応答
キーワード：ナノ粒子暴露実験、海洋生態系、単細胞真核生物、解毒作用
Engineered nanomaterials in particular metal-based nanoparticles (NPs) provide benefits for human society, as applications in the multiple fields: IT, medicals, energy, and personal cares. However, NPs wastes now spread out over the world oceans and most likely have harmful effects to marine ecosystem as novel pollutants. Understanding of the effect of NPs contaminated environment on marine life become urgent and serious issue. In marine ecosystem, foraminifers, unicellular eukaryotes bearing calcareous shells, play important roles for supporting food web and carbon cycles. Foraminifers have three unique features: wide distribution in marine environments including polluted area, large-sized cell (> 200 µm), and uptake of external materials into cell through pseudopodia. These characters provide us an excellent condition for exposure experiments to examine physiological reaction (i.e., stress) to NPs additive seawater. Ciacci et al. (2019) unveiled that foraminifers generated reactive oxygen species (ROS) after uptake of NPs into the cells under three (TiO2, SiO2, and polystyrene nanoparticles) different NPs exposure experiments based on confocal laser scanning microscopic (CLSM) observation. Furthermore, Ishitani et al. (under review) successfully performed a time-series (1–24 hours) TiO2 exposure experiments with foraminifers and traced metabolic pathway and its changes using a comprehensive approach of CLSM observation and transcriptomes. Foraminifers endocytose TiO2 NPs and generate abundant ROS in the first hour of experiment, but expel such foreign materials encapsulated in ceramides after 24 hours. These discoveries indicate foraminifers have a detoxification mechanism of TiO2 NPs. The present study investigated the location of expelled NPs and any ecophenotypic changes on foraminifers through a long-term culture examination.
A strain of benthic foraminifer, Ammonia veneta, were cultured in 1 ppm TiO2 NPs additive seawater for 3 months. This organism grew up and reproduced clones every 3–4 weeks as same as controls, which were incubated in seawater. During growth, foraminifers often discharged mucus. We embedded this mucus in the 1% low-melt agarose gel with filtered seawater and made semi-thin sections. Moreover, we made the precise cross-sections of the foraminiferal calcareous shells. The mucus and shell sections were applied to the field emission scanning electron microscope (FE-SEM)-energy dispersive spectroscopy (EDS) analysis and the focused ion bean scanning electron microscope (FIB-SEM) to detect titanium, respectively. These analyses showed the absence of titanium in the shells but detected it in the mucus. In addition, nitrogen was co-detected from the TiO2 NP embedding mucus, suggesting the mucus is composed of ceramides. These results suggest TiO2 NPs are packed only in the mucus, and led a new insight into prevention of the TiO2 NPs spread over marine environment. Ceramide envelop inhibits the catalytic effect of metal-based NP driven on its surface, and then it could be difficult for other marine organisms to uptake inside the cells. On the other hand, some clonal descendants made deformed shells over three generations. This suggests a possibility of ecophenotypic changes due to toxic effect of TiO2 NPs. Our results could give us a hint to a potential innovative by which NPs can be detoxified in marine unicellular eukaryote, though genotoxic effects are still unknown.
Ciacci et al. Nanoparticle-biological interactions in a marine benthic foraminifer. Sci. Rep. 9, 19441 (2019).
Ishitani et al. Fascinating strategies of marine organisms to avoid the risk of TiO2 nanoparticles. (under review).
A strain of benthic foraminifer, Ammonia veneta, were cultured in 1 ppm TiO2 NPs additive seawater for 3 months. This organism grew up and reproduced clones every 3–4 weeks as same as controls, which were incubated in seawater. During growth, foraminifers often discharged mucus. We embedded this mucus in the 1% low-melt agarose gel with filtered seawater and made semi-thin sections. Moreover, we made the precise cross-sections of the foraminiferal calcareous shells. The mucus and shell sections were applied to the field emission scanning electron microscope (FE-SEM)-energy dispersive spectroscopy (EDS) analysis and the focused ion bean scanning electron microscope (FIB-SEM) to detect titanium, respectively. These analyses showed the absence of titanium in the shells but detected it in the mucus. In addition, nitrogen was co-detected from the TiO2 NP embedding mucus, suggesting the mucus is composed of ceramides. These results suggest TiO2 NPs are packed only in the mucus, and led a new insight into prevention of the TiO2 NPs spread over marine environment. Ceramide envelop inhibits the catalytic effect of metal-based NP driven on its surface, and then it could be difficult for other marine organisms to uptake inside the cells. On the other hand, some clonal descendants made deformed shells over three generations. This suggests a possibility of ecophenotypic changes due to toxic effect of TiO2 NPs. Our results could give us a hint to a potential innovative by which NPs can be detoxified in marine unicellular eukaryote, though genotoxic effects are still unknown.
Ciacci et al. Nanoparticle-biological interactions in a marine benthic foraminifer. Sci. Rep. 9, 19441 (2019).
Ishitani et al. Fascinating strategies of marine organisms to avoid the risk of TiO2 nanoparticles. (under review).