Microbiology

Daylight Robbery on the High Seas

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Science  14 Jul 2000:
Vol. 289, Issue 5477, pp. 217
DOI: 10.1126/science.289.5477.217b

Mesodinium rubrum is a common ciliate member of marine plankton and contributes to non-toxic red tides. Its classification is problematic as it contains several non-ciliate mitochondria and chloroplasts, apparently has no nucleus, and seems to be an obligate phototroph. It does have some capacity to synthesize chlorophyll and, unlike other plastid-retaining ciliates, can use inorganic nutrients dissolved in the water column.

Gustafson et al. succeeded in culturing this rather fragile organism and found that cultures would grow only in the presence of a cryptophyte alga, Teleaulax acuta. Despite its mouthless state, the ciliate was able to ingest the algae and, as a result, changed from colorless to bright pink. Several days after a binge, a M. rubrum culture had preferentially retained the cryptophyte's plastids, actively multiplied, and doubled its photosynthetic capacity. The ciliate seems to appropriate the plastids to replace aging plastids or to top up after several rounds of cell division, hence maintaining itself by a life of crime. — CA

Nature405, 1049 (2000).

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