Scientists have found that one of the genes necessary for jellyfish to sting is similar to a gene in bacteria, suggesting the ancestors of the marine animal picked up the gene from microbes. “The result was a great surprise,” developmental biologist Nicolas Rabet of the Pierre and Marie Curie University in Paris, France, who led the team, told Nature News.
“This kind of horizontal gene transfer is often neglected, and could sometimes be more important than we thought,” he added. Unlike vertical gene transfer from parent to offspring, the horizontal variety happens between organisms, or even between different species.
Common in microbes, it has only been described a few times in animals. The gene in question codes for a subunit of poly-gamma-glutamate (PGA) synthase. PGA itself is a major component of stinging cells. The gene appears in all known genomes of creatures from the phylum cnidaria, which includes jellyfish, anemones and corals.
By collecting positive ions, PGA allows the cells to regulate their osmotic pressure; a sudden change in that pressure launches a poisonous barb. In bacteria, the same compound can form a protective capsule. It also gives the fermented Japanese food natto its stringy texture and pungent aroma.
Using phylogenetic analysis, Rabet and his colleagues found that the cnidarian gene fits well into the bacterial family tree. They also showed that the gene turns on in at least one jellyfish, Clytia hemisphaerica. The same gene pops up in certain sponges, worms and fungi, suggesting it jumped between species more than once, the scientists said. It is not yet clear how the transfer might have occurred, or why this particular gene would be so well travelled.
According to Michael Syvanen, who studies comparative genomics at the University of California, Davis. other possibilities cannot be ruled out. “There are other explanations for the incongruencies they see in the tree,” said Casey Dunn, an evolutionary biologist who studies phylogenetic problems at Brown University in Providence, Rhode Island. For instance, the gene could be vertically transferred from a distant progenitor, before being lost from some organisms. It may be possible that more than one animal independently evolved the gene. “At the end of the day, it will probably take far more data to paint a conclusive picture of what’s happening,” said Dunn.