Monday, September 03, 2007

Host-Parasite Intimacy--Reaching a New Level

One Species' Genome Discovered Inside Another's. I thought this was an interesting article, and it comes out of the research institute where I used to work (now known as the J. Craig Venter Institute), although there's only one person I know in the author list. The actual article is Widespread Lateral Gene Transfer from Intracellular Bacteria to Multicellular Eukaryotes in the latest issue of Science.

Wohlbachia species are parasites of insects and other invertebrates, passed from one host generation to the next inside the germ cells. Wohlbachia genes have been discovered inserted into host genomes, but this paper documents cases in which the entire bacterial genome has been so inserted.

Lateral gene transfer between bacterial species is a common phenomenon, and has made me pessimistic about deducing evolutionary history of bacteria. This finding could throw a monkey wrench in molecular insect phylogeny as well. It's also likely to send genome sequencers to recheck their published data. In sequencing eukaryotic genomes, you often get bacterial genome contamination, and much of the software used in the process automatically recognizes and discards bacterial sequences. Someone's going to have to distinguish between contamination and real sequence data. (Glad it's not me.)

Widespread Lateral Gene Transfer from Intracellular Bacteria to Multicellular Eukaryotes,

Julie C. Dunning Hotopp, Michael E. Clark, Deodoro C. S. G. Oliveira, Jeremy M. Foster, Peter Fischer, Monica C. Munoz Torres, Jonathan D. Giebel, Nikhil Kumar, Nadeeza Ishmael, Shiliang Wang, Jessica Ingram, Rahul V. Nene, Jessica Shepard, Jeffrey Tomkins, Stephen Richards, David J. Spiro, Elodie Ghedin, Barton E. Slatko, Herve Tettelin, John H. Werren

Published Online August 30, 2007, Science, Reports

Although common among bacteria, lateral gene transfer (the movement of genes between distantly related organisms) is thought to occur only rarely between bacteria and multicellular eukaryotes. However, the presence of endosymbionts, such as Wolbachia pipientis, within some eukaryotic germlines may facilitate bacterial gene transfers to eukaryotic host genomes. We therefore examined host genomes for evidence of gene transfer events from Wolbachia bacteria to their hosts. We found and confirmed transfers into the genomes of 4 insect and 4 nematode species that range from nearly the entire Wolbachia genome (>1 megabase) to short (<500 base pairs) insertions. Potential Wolbachia to host transfers were also detected computationally in three additional sequenced insect genomes. We also show that some of these inserted Wolbachia genes are transcribed within eukaryotic cells lacking endosymbionts. Therefore, heritable lateral gene transfer occurs into eukaryotic hosts from their prokaryote symbionts, potentially providing a mechanism for acquisition of new genes and functions.

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