Australian researchers have discovered an entirely new way of sharing DNA, in a study of Antarctic microbes.

A team of UNSW scientists has been studying water samples from some of the saltiest lakes in Antarctica.

Their latest report details the discovery of a strain of the Antarctic salt-loving microbes that contains plasmids – small molecules of DNA which can replicate independently in a host cell, and which often contain genes useful to an organism.

“Unlike viruses, which encase themselves in a protective protein coat, plasmids usually move around by cell to cell contact, or as a piece of naked DNA,” says UNSW scientist Professor Rick Cavicchioli.

“But the plasmids that we found in the Antarctic microbes were masquerading as viruses. They produced proteins which went into the host’s membrane, which then allowed the membrane to bud off containing the plasmid DNA.

“The budded membranes, called membrane vesicles, allowed the plasmids to infect microbes of the same species that did not have any plasmids present, and then replicate themselves in the new host,” he says.

The experts say it is the first time this mechanism has been documented, and that it could be an evolutionary forerunner to some of the more structured protective coats that viruses have developed to help them spread and become successful invaders.

“This finding suggests some viruses may have evolved from plasmids,” first author Dr Susanne Erdmann says.

The study has been published in the journal Nature Microbiology.

The Antarctic microbes studied by the researchers are called haloarchaea and are known to be pretty promiscuous, constantly swapping DNA between themselves.

They live in Deep Lake, a 36-metre deep lake that is so salty it remains in liquid form down to a temperature of minus 20 degrees.

The lake, which is about five kilometres from Australia’s Davis Station, was formed around 3500 years ago when the Antarctic continent rose, isolating a section of ocean.

Haloarchaea microbes containing the plasmids were isolated from very rare water samples collected from the Rauer Islands about 35 kilometres further away.

“We also discovered that the plasmids could take some of the DNA from the host microbe, integrate it into their own DNA, produce membrane vesicles around themselves, and then go off and infect other cells,” says Professor Cavicchioli.

“The findings are therefore relevant to Antarctic science as well as biology as a whole.”