Some terms: I'll use the terms "bacteria" and "animal" to represent the proper scientific terms "prokaryote" and "metazoan."
Rotifer: a tiny freshwater invertebrate that spins as it swims. I remember they showed us a few under the microscope in high school bio.
Horizontal transfer: the movement of genes from one organism to another other than through direct inheritance. This can happen in bacteria by direct contact and shuttling of DNA through a thin tube, for example. However, horizonal transfer is very rarely seen in animals.
Introns: DNA normally codes for proteins by "spelling out" amino acids. DNA that doesn't code for proteins don't spell out anything. When coding DNA (exons) is interrupted by non-coding DNA (don't worry, they get cut out later), this non-coding DNA is called an intron:
The basic results: The researchers found that, inside a certain type of rotifer, clusters of genes exist that don't look similar to genes in any known animal, but rather look very much like bacterial genes. For example, the Alr gene makes an enzyme involved in building bacterial cell walls, something animals don't do. (Most likely this Alr gene doesn't do much of anything in the rotifer, according to the article, but some of the other bacterial genes function just fine). So these genes must somehow have jumped from existing bacteria to the rotifers, somewhere back in history.
Even more surprising, some of these genes of bacterial origin have acquired something that bacterial genes don't normally have: introns. Animal genes have introns, meaning that what likely happened is that the bacterial genes jumped, then were slowly changed over evolutionary time (thousands or millions of years) to become animal-like (ie possessing introns).
What this means for evolution: Genetic diversity within and between different animals is both conservative (many of the same genes appear across different animals) and wide (many if not most animal types have genes that are specific to it). How does this diversity occur? It happens many ways, but the one in this article is one of the most surprising. It may be especially enhanced in the rotifer, according to the authors, since rotifers can survive being dried out and reconstituted, which may cause nearby bacteria to shed their DNA into the rotifer in between. Nevertheless, this kind of bacterial-animal horizontal gene transfer - now that we know it exists - could point to one of the ways in the farther past that some of today's genetic diversity could have come about. Or it may just be a weird rotifer thing. Time will tell.
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