Borg, a new form of DNA?

Microbiologist Jillian Banfield didn’t expect what she found when examining mud samples from swamps in the American West. While searching with her colleagues for the genetic material of phages – viruses that kill bacteria – the researcher at the University of California, Berkeley, discovered some very strange DNA. They do not appear to come from a virus, bacteria, or archaea (single-celled organisms that make up one of the three main areas of the tree of life, along with bacteria and eukaryotes). The researchers named their discovery “borg”, referring to a type of alien from the science fiction series Star Trek, capable of assimilating individuals into the collective consciousness. In fact, this genetic makeup will incorporate the genes from its host cell into it. This is amazing The study was previously published on biorxiv.org And it still needs peer review.

Normally, most microorganisms contain one or two small chromosomes that contain the genetic material that encodes all of their essential functions. Some also contain “extrachromosomal” DNA, for example in the form of plasmids (circular DNA molecules found mainly in bacteria). But the tower has exceptional characteristics that make it difficult to classify. These molecules are large strands of DNA, 600,000 to 1 million base pairs long, or up to one-third the size of the largest chromosome in the host microorganism. Currently, researchers do not know whether the genes in these strands were expressed or not, and the vast majority of them are still unknown. However, they determined that these DNA strands were present in the methanotrophic archaea, of class methanopyridinesSingle-celled organisms that use methane as an energy source.

Unfortunately, this only heightens the puzzle. If the lacunae are found in a host cell, they do not appear to be part of the host cell’s genome. They are linear, while Archean chromosomes are circular, and they are larger than strands of DNA outside of the usual chromosomes such as plasmids. However, and that’s what earned them their name, Burgess seem to contain genes from their host. What’s more, those responsible for methane metabolism, cell wall structure and even the synthesis of ribosomal proteins – which allow messenger RNA to be translated into proteins – all essential functions are usually encoded by genes not on the outside. Chromosomes!

For Jillian Banfield, all these amazing characteristics indicate that Borgs are a completely new type of genetic element, not yet known. They could be the remains of an ancient microorganism that these archaea assimilated, giving rise to a new form of endosymbiosis – a process similar to the one that gave birth to the mitochondria in our cells. But the hypothesis of viral DNA or the existence of a new form of plasmid cannot be ruled out. Some, more cautious, researchers are turning to this option, particularly in light of the discovery of a giant, linear, unique plasmid in bacteria ten years ago. Streptomyces. Furthermore, because at present it is still impossible to cultivate archaea methanopyridines In the laboratory, this work is based solely on genetic sequences reconstructed from DNA fragments obtained from sludge samples. So errors in assembly could have occurred.

More genetic analysis will be necessary, and the ideal is to one day succeed in cultivating archaea that carry this unique structure within them. Meanwhile, Jillian Banfield already sees the potential environmental applications of such a discovery: as methanopyridines As methane can be “digested”, a better understanding of the genes responsible for this ability could one day be used to control pollution from this gas.