Evidence of horizontal gene transfer. (A) The unicellular red alga Galdieria sulphuraria belongs to the order Cyanidiales, clearly within the eukaryotic branch of the evolutionary tree. (B) Within the completely sequenced G. sulphuraria genome, two ORFs encode proteins involved in transport of arsenate ions across membranes. Alignment of these ORFs against orthologs from a variety of species reveals that these pumps are most closely related to their bacterial counterparts, suggesting that a horizontal gene transfer event occurred during the evolution of this species.
[(A) Information from Dr. Gerald Schönknecht; (B) Information from G. Schönknecht et al. Science 339:1207–