by Merry and ElioOrganelles were endosymbionts that either made good or were enslaved, depending on your point of view. Either way, some of their genes now reside in the nuclear genome of their eukaryote host. We also know that there are some bacterial endosymbionts
http://schaechter.asmblog.org/schaechter/2008/11/jumping-genes-wolbachia...
Horizontal gene transfer in eukaryotic evolution.
Keeling PJ (2008) Nat Rev Genet.Phylogenomics of the reproductive parasite Wolbachia pipientis wMel: a streamlined genome overrun by mobile genetic elements.
Wu M (2004) PLoS Biol.Phylogenetic relationships of the Wolbachia of nematodes and arthropods.
Fenn K (2006) PLoS Pathog.Widespread lateral gene transfer from intracellular bacteria to multicellular eukaryotes.
Hotopp JC (2007) Science.Genome fragment of Wolbachia endosymbiont transferred to X chromosome of host insect.
Kondo N (2002) Proc Natl Acad Sci U S A.