In the Star Trek TV series, of which he is a new movie is coming, i Borg they are cyber aliens who they assimilate humans and other creatures as a means of achieving perfection. So when Jill Banfield, a geomicrobiologist at the University of California, Berkeley, sifted through DNA in her backyard mud and discovered a strange linear chromosome that included genes from a variety of microbes, her son Trekkie proposed to name it after them. .
The new type of mystery genetic material, perhaps it was part of a viral genome, perhaps it was a strange bacterium, or perhaps it was just an independent piece of DNA existing outside the cells. Whatever it is, it is “Quite exciting”says W. Ford Doolittle, an evolutionary biologist from Dalhousie University who was not involved in the work.
Researchers have found many examples of DNA floating independently outside the chromosome or chromosomes that make up an organism’s standard genome. Small loops called plasmids, for example, they exist within microbes and ferry genes to counter antibiotics between different types of bacteria.
But Banfield wasn’t looking for DNA that could move between organisms. Instead, she and graduate student Basem Al-Shayeb were looking for viruses that infect archaea, a type of microbe often found in oxygen-free places.
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They dug 1 meter or more below the surface and collected mud samples that could harbor archaea and their viruses. Next, they sequenced each stretch of DNA in the samples and used sophisticated computer programs to look for sequences that indicate a virus rather than any other organism.
“We started with a piece of mud and 10 trillion pieces of DNA”says Banfield. One sample, taken from the mud on his property, contained a gene-filled stretch of DNA nearly 1 million bases long, and more than half of the genes were new.
This linear stretch of DNA also had a particular pattern of bases at the beginning and end, distinct stretches of repetitive DNA between its genes, and two points along the sequence where DNA duplication could begin, which indicated that the Borg could make copies of themselves. Together, this suggested it wasn’t just a random blend of genes.
After identifying the first Borg sequence, the researchers began scanning the microbial DNA in public databases to see if they could find something similar. They found some variations in the Colorado groundwater: there, the first alleged Borg appeared about 1 meter deep and it became more abundant as it went deeper.
Other versions emerged in the DNA from the exhaust of an abandoned mercury mine in Napa, California, and from a shallow riverbed of the East River in Colorado. Overall, the researchers isolated 23 sequences that they think may be Borg and identified 19 as having all the characteristics of the first Borg they discovered, they write this week on the prepress server. bioRxiv.
Some are nearly 1 million bases long. “I don’t think anything else that has been discovered is as big as these guys”, among the previously known extrachromosomal DNA elements, Doolittle says.