Present address: Department of Biology, Stanford University, 371 Serra Mall, Stanford, California 94305, USA.
PHOTOACCLIMATION IN THE PHOTOTROPHIC MARINE CILIATE MESODINIUM RUBRUM (CILIOPHORA)1
Article first published online: 1 MAR 2011
© 2011 Phycological Society of America
Journal of Phycology
Volume 47, Issue 2, pages 324–332, April 2011
How to Cite
Moeller, H. V., Johnson, M. D. and Falkowski, P. G. (2011), PHOTOACCLIMATION IN THE PHOTOTROPHIC MARINE CILIATE MESODINIUM RUBRUM (CILIOPHORA). Journal of Phycology, 47: 324–332. doi: 10.1111/j.1529-8817.2010.00954.x
Received 24 May 2010. Accepted 13 September 2010.
- Issue published online: 4 APR 2011
- Article first published online: 1 MAR 2011
- Geminigera cryophila;
- light limitation;
- Mesodinium rubrum;
- Myrionecta rubra;
- quantum yield for growth
Mesodinium rubrum (=Myrionecta rubra), a marine ciliate, acquires plastids, mitochondria, and nuclei from cryptophyte algae. Using a strain of M. rubrum isolated from McMurdo Sound, Antarctica, we investigated the photoacclimation potential of this trophically unique organism at a range of low irradiance levels. The compensation growth irradiance for M. rubrum was 0.5 μmol quanta · m−2 · s−1, and growth rate saturated at ∼20 μmol quanta · m−2 · s−1. The strain displayed trends in photosynthetic efficiency and pigment content characteristic of marine phototrophs. Maximum chl a–specific photosynthetic rates were an order of magnitude slower than temperate strains, while growth rates were half as large, suggesting that a thermal limit to enzyme kinetics produces a fundamental limit to cell function. M. rubrum acclimates to light- and temperature-limited polar conditions and closely regulates photosynthesis in its cryptophyte organelles. By acquiring and maintaining physiologically viable, plastic plastids, M. rubrum establishes a selective advantage over purely heterotrophic ciliates but reduces competition with other phototrophs by exploiting a very low-light niche.