DNA Barcoding: Identifying Organisms at the Molecular Level

fungiHow would you identifying all the species in the picture? You could consult a field guide, ask a mycologist (a person who specializes in fungi), or you could sequence its DNA. This last choice is becoming increasingly popular and is known as DNA barcoding. DNA barcoding uses short polymorphic segments of DNA to classify an organism as belonging to a particular species.

In order to enable barcoding scientist needed to first find a place in the genome that was an ideal mixture of variable and conserved. The center region of this sequence had to differentiated between even closely related species but not differ significantly between individuals within a species. On either side of this variable region they needed to find sequences that were nearly identical between all the organisms in a kingdom so that universal primers could be used. Discovering such a place was an intense search. Today we have CO1 for animals, ITS for fungi, and rbcL & matK for plants.

Analyze DNA sequences in your classroom! © Edvotek 2014
Analyze DNA sequences in your classroom! © Edvotek 2014

Sequencing is used to reveal the precise order of the nucleotides within these barcode regions. In Sanger sequencing each run is comprised of a single region from a single specimen. This works well when one specimen is being tested. Sometimes, especially when dealing with microbial diversity, the sample to be sequenced is a mixture of different species. In this case high throughput sequencing is used. High throughput sequencing, also known as massively parallel sequences, allows many sequences of DNA to be processed from the same sample.

Today barcoding is being used to look at biodiversity in new ways and new places. Hard to examine organism such as bacteria are being categorized in record numbers. Biodiversity inventories are more objective and accessible. New habitat such as a column of soil, the stomach of a bird, and the nectar of a flower are being examined and characterized. Barcoding is an excellent example of how biotechnology is contributing to diverse areas of science.