STORY OF A NOVEL DNA

 MASSIVE DNA 'BORG'

 DATE:- 20.07.21

Scientists analyzing samples from muddy sites in the western United States have found novel DNA structures that seem to scavenge and ‘assimilate’ genes from microorganisms in their environment, much like the fictional Star Trek ‘Borg’ aliens who assimilate the knowledge and technology of other species.

These extra-long DNA strands, which the scientists named in honor of the aliens, join a diverse collection of genetic structures — circular plasmids, for example — known as extrachromosomal elements (ECEs). Most microbes have one or two chromosomes that encode their primary genetic blueprint. But they can host, and often share between them, many distinct ECEs. These carry non-essential but useful genes, such as those for antibiotic resistance.

Borgs are a previously unknown, unique and “absolutely fascinating” type of ECE, says Jill Banfield, a geo microbiologist at the University of California, Berkeley.

Unlike anything seen before

Borgs are DNA structures “not like any that’s been seen before”, says Brett Baker, a microbiologist at the University of Texas at Austin. Other scientists agree that the find is exciting, but have questioned whether Borgs really are unique, noting similarities between them and other large ECEs.

Their vast size, ranging between more than 600,000 and about 1 million DNA base pairs in length, is one feature that distinguishes Borgs from many other ECEs. In fact, Borgs are so huge that they are up to one-third of the length of the main chromosome in their host microbes, Banfield says.

Banfield studies how microbes influence the carbon cycle — including the production and degradation of methane, a potent greenhouse gas — and, in October 2019, she and her colleagues went hunting for ECEs containing genes involved in the carbon cycle in Californian wetlands. There, they found the first Borgs and later identified 19 different types from this and similar sites in Colorado and California.

Borgs seem to be associated with archaea, which are single-celled microorganisms distinct from bacteria. Specifically, those Banfield and her team have discovered are linked to the Methanoperedens variety, which digest and destroy methane. 

Costs and benefits

Assuming Borgs are real, maintaining such a massive ECE would be costly for Methanoperedens, Banfield and colleagues say, so the DNA structures must provide some benefit. To learn what that might be, the researchers analyzed the sequences of hundreds of Borg genes and compared them with known genes.

Borgs seem to house many genes needed for entire metabolic processes, including digesting methane, says Banfield. She describes these collections as “a toolbox” that might super-charge the abilities of Methanoperedens.

                      'Borg' image under Scanning Electron Microscopy

                         River Colorado from where DNA Borg has been found

Reference :-

Al-Shayeb, B. et al. Preprint at bioRxiv https://doi.org/10.1101/2021.07.10.451761 (2021).