To survive in extreme environments—like hot sulfur springs—it seems that the unicellular red algae Galdieria sulphuraria couldn’t rely on its own genome. Instead, these simple organisms borrowed genes from bacteria and archaea that protect the algae from otherwise unbearable heat and toxic acidic conditions, according to a new study published today (1).
“I think what is special is that we clearly show that G. sulphuraria is what it is because of the genes it got from bacteria,” said study author Gerald Schönknecht, an associate professor at Oklahoma State University in Stillwater.
He called the finding “the tip of the iceberg.” With more eukaryotic and bacterial genomes becoming available, there could be additional examples of unicellular eukaryotes that acquire genes for crucial functions from bacteria.
Published March 8 in Science, the study began a decade ago when the National Science Foundation awarded Andreas Weber, then at Michigan State University in East Lansing, $1.4 million to lead an international team to sequence G. sulphuraria. Most of the team’s work was done in 2004 and 2005, before next-generation sequencing became widely available.
In 2007, Schönknecht started entering the algae’s protein sequences into the National Center for Biotechnology Information’s BLAST software to search for similar proteins. To his surprise, he found matches with many bacterial sequences. “It quickly became obvious that there were quite a few genes and proteins that we analyzed which were so similar to bacteria that they had to originate from bacteria,” Schönknecht said.
For example, one G. sulphuraria sequence matched a gene encoding a bacterial arsenic pump, a biological feature that had never been seen in eukaryotes before. Other clusters of the G. sulphuraria genome contain genes similar to those for archaeal soluble ATPases, which are thought to promote survival at extremely high temperatures.
Because the results seemed so unbelievable, the team spent much time ruling out alternative explanations. The group also set up a bioinformatics pipeline to help them map all of G. sulphuraria’s 6623 genes and their evolutionary origins, finding that at least 5% of the algae’s genes were acquired through horizontal gene transfer, probably several hundred million years ago.
Some of these prokaryotic genes might have biotechnology applications. For example, they could be used to genetically engineer crops resistant to salt stress by introducing cellular transporters that remove excess salt from the cytosol or to produce hardier algae for use in biofuel production.
To verify the functions of these borrowed genes and learn more about roles they play in G. sulphuraria, Schönknecht plans to sequence more genomes from the G. sulphuraria’s family, Cyanidiophyceae, whose other members are also extremophiles. “I expect that there are much more surprises out there,” Schönknecht said.
1. Schönknecht, G., W.-H. Chen, C. M. Ternes, G. G. Barbier, R. P. Shrestha, M. Stanke, A. Bräutigam, B. J. Baker, J. F. Banfield, R. M. Garavito, et al. 2013. Gene transfer from bacteria and archaea facilitated evolution of an extremophilic eukaryote. Science 339(6124):1207-1210.
2. Bowler, C., A. E. Allen, J. H. Badger, J. Grimwood, K. Jabbari, A. Kuo, U. Maheswari, C. Martens, F. Maumus, R. P. Otillar, et al. 2008. The phaeodactylum genome reveals the evolutionary history of diatom genomes. Nature 456(7219):239-244.