Genomic analysis of the hairy single-celled ciliate Tetrahymena thermophila (pictured) suggests that ciliates may once have been photosynthetic. This finding supports the controversial 'chromalveolate hypothesis', which proposes a common photosynthetic ancestor for two groups of single-celled eukaryotes: the chromists and the alveolates.
Searching through the tens of thousands of proteins predicted from the genome of T. thermophila, an alveolate, Debashish Bhattacharya and his colleagues at the University of Iowa in Iowa City identified 16 proteins potentially derived from a photosynthetic algal ancestor. All 16 were also present in another ciliate, Paramecium tetraurelia.
The researchers argue that it is more likely that the ciliates had a photosynthetic ancestor but later lost the ability to photosynthesize than that they absorbed the genes by horizontal gene transfer.
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Evolution: Photosynthetic ancestors. Nature 454, 141 (2008). https://doi.org/10.1038/454141c
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DOI: https://doi.org/10.1038/454141c
