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Dynamics of Sequestered Cryptophyte Nuclei in Mesodinium rubrum during Starvation and Refeeding
Miran Kim1, Kirstine Drumm1, Niels Daugbjerg2
1Marine Biological Section, Department of Biology, University of Copenhagen Helsingør, Denmark.
Abstract:
The marine mixotrophic ciliate Mesodinium rubrum is known to acquire chloroplasts, mitochondria, nucleomorphs, and nucleus from its cryptophyte prey, particularly from species in the genera, Geminigera and Teleaulax. The sequestered prey nucleus and chloroplasts are considered to support photosynthesis of M. rubrum. In addition, recent studies have shown enlargement of the retained prey nucleus in starved M. rubrum and have inferred that enlargement results from the fusion of ingested prey nuclei. Thus far, however, little is known about the mechanism underlying the enlargement of the prey nucleus in M. rubrum. Here, we conducted starvation and refeeding studies to monitor the fate of prey nuclei acquired by M. rubrum when feeding on Teleaulax amphioxeia and to explore the influence of the retained prey nucleus on photosynthesis of M. rubrum. Results indicate that enlargement of the prey nucleus does not result from fusion of nuclei. Furthermore, the enlarged prey nucleus does not appear to divide during cell division of M. rubrum. The presence of a prey nucleus significantly affected photosynthetic performance of M. rubrum, while the number of retained chloroplasts had little influence on rate of carbon fixation. We interpret results within the context of a model that considers the dynamics of ingested prey nuclei during division of M. rubrum.
Insights
The marine ciliate Mesodinium rubrum retains prey nuclei, but these do not fuse or divide. The prey nucleus significantly impacts M. rubrum's photosynthesis, not the number of chloroplasts.
Area of Science:
- Marine biology
- Protistology
- Photosynthesis research
Background:
- Mesodinium rubrum is a mixotrophic ciliate that sequesters organelles, including nuclei, from its cryptophyte prey.
- The retained prey nucleus and chloroplasts are thought to support M. rubrum's photosynthesis.
- Previous studies suggested prey nucleus enlargement in M. rubrum results from nuclear fusion, but mechanisms remain unclear.
Purpose of the Study:
- To investigate the fate of prey nuclei in M. rubrum during starvation and refeeding.
- To explore the influence of the retained prey nucleus on M. rubrum's photosynthetic activity.
- To elucidate the mechanism of prey nucleus enlargement in M. rubrum.
Main Methods:
- Starvation and refeeding experiments with M. rubrum and its prey Teleaulax amphioxeia.
- Monitoring of prey nucleus behavior and size within M. rubrum.
- Assessment of M. rubrum's photosynthetic performance and carbon fixation rates.
Main Results:
- Prey nucleus enlargement in M. rubrum does not occur through nuclear fusion.
- The enlarged prey nucleus does not appear to divide during M. rubrum cell division.
- The presence of a prey nucleus significantly influenced M. rubrum's photosynthetic performance, while chloroplast number had minimal effect on carbon fixation.
Conclusions:
- The mechanism of prey nucleus enlargement in M. rubrum is not nuclear fusion.
- The retained prey nucleus plays a crucial role in M. rubrum's photosynthesis, independent of chloroplast number.
- A model is proposed to explain the dynamics of ingested prey nuclei during M. rubrum division.