Photoacclimation in the phototrophic marine ciliate mesodinium rubrum (ciliophora)

Holly V. Moeller, Matthew D. Johnson, Paul G. Falkowski

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


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 0.5μmolquanta·m-2·s-1, and growth rate saturated at ∼20μmolquanta· 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.

Original languageEnglish (US)
Pages (from-to)324-332
Number of pages9
JournalJournal of Phycology
Issue number2
StatePublished - Apr 2011

All Science Journal Classification (ASJC) codes

  • Aquatic Science
  • Plant Science


  • Ciliate
  • Geminigera cryophila
  • Karyoklepty
  • Light limitation
  • Mesodinium rubrum
  • Myrionecta rubra
  • Photoacclimation
  • Quantum yield for growth


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