GoKawiilRyan Kelly is in awe of what floats invisibly in the air.
“It is completely mind-blowing,” says Kelly, who studies environmental DNA (eDNA) at the University of Washington in Seattle. “We are absolutely surrounded by information in the form of DNA and RNA, at all times.”
Rare bird’s detection highlights promise of ‘environmental DNA’
Scientists have long pulled DNA from water and soil, but they have only just started to see the air as a source of genetic information. Over the past decade or so, researchers have been learning how to measure airborne DNA, study its abundance and use it to put together a picture of an ecosystem’s inhabitants and health. Airborne DNA is being used to monitor individual species, and being trialled as a way to detect invasive species or attacks with biological weapons. It is also being tested as a way to judge the success of conservation efforts.
The technique promises to link “the whole [of] biodiversity, the whole world together with a single assay that’s really rapid and that can even be done in the field and analysed in the cloud”, says David Duffy, a researcher who specializes in wildlife disease genomics at the University of Florida in St Augustine.
But there is still a lot to pin down, such as how fast DNA decays in the air and how far it travels. Some genetic material pulled from the air comes from humans, and several scientists are concerned that when using the technique for conservation research, it could inadvertently reveal people’s ethnicity or whether a person has a genetic disorder — and even be used to identify individuals.
Clouds of DNA
Scratch your head and you’ll release DNA-rich cellular material into the air. There, it will mingle with DNA from myriad other sources: your own and others’ exhalations and exfoliations, fragments of hair, feathers, excrement, pollen and spores, and microorganisms such as viruses and microalgae. This DNA, which can include segments that are tens of thousands of base pairs long, will then wander the air for perhaps a few days, often clinging to dust particles. It can travel distances that range from a few metres to several thousand.
Although eDNA is already collected routinely from water, snow and soil, to gather information about biodiversity or to track contaminants or viruses, scientists have not typically monitored sources of DNA in air other than pollen and spores — robust packages designed to travel on the breeze.
But, in the early 2010s, various ecologists began to wonder whether air might contain useful DNA traces beyond those wrapped in such windborne bundles. In 2013, biologists Matt Clark at the Natural History Museum in London and Richard Leggett at the Earlham Institute in Norwich, UK, took air samples in a greenhouse and outside it.
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