DNA DETECTION
Donald Hobern is executive secretary of the International Barcode of Life Consortium (iBOL), an organisation working to use DNA to reveal species across the globe, including their dynamics and interactions. As the iBOL website states: ‘While study has delivered a basic understanding of biodiversity, it cannot discover and identify species on a planetary scale. Our vision is to illuminate biodiversity for the benefit of all life.’ iBOL is centred on DNA barcoding, which involves isolating DNA from a specimen (which might be a small organism or just a small part of an organism) and turning it into a barcode sequence that is then stored in a searchable reference database. You don’t need to map the whole genome of a specimen (although other projects are underway that do so, such as the Earth Biogenome Project); for animals, the barcode is taken from a small section of 650 base pairs in the loop of DNA found in the mitochondria of cells. ‘Within this loop, a difference in DNA between two organisms of a few per cent [the amount varies within different taxonomic groups] seems fairly reliably to match, for many groups, the sort of difference that would traditionally identify different species,’ says Hobern. ‘The level of difference is not a black-and-white test, but it’s a very useful tool, because we can standardise it across most animals and these days it’s relatively cheap.’ The first iBOL research programme barcoded 500,000 species, reflecting an investment of US$150 million by research organisations in 25 nations. Its second programme, BIOSCAN, aims to extend barcode coverage to 2.5 million species by 2026. Hobern points out that there’s a wide range of uses for such a database. Not only could it aid taxonomists in their work, but sequencing DNA from a sample and comparing it to the reference database can verify that fish being sold are indeed one of the species listed on the packet, rather than a threatened species, or enable rapid detection of rare forest timbers or bushmeat in a market. ‘One of the other advantages is that, not only can you do this with a bit of flesh, you can do it with all kinds of other samples in the environment,’ he says. ‘If you take soil, you’ll find trace DNA from animals that have passed there and that have either dropped skin cells or left faeces behind. If you take water from streams, you can detect what fish are elsewhere in the stream.’ This is known as a ‘metagenomic’ study and it can very quickly provide a genetic snapshot of an entire ecosystem. With the cost of sequencing coming down all the time, Hobern is looking forward to seeing environmental sensors that are based on cheap portable DNA sequencers, which could simply be placed in the field or at sea and then sequence the DNA of all of the species present in that area. ‘At that point, the world’s a different place, and we’re probably not that far from it,’ he says.