DNA Barcoding: a new tool with wide array of applications

Abstract

DNA barcoding is a new term introduced in to scientific literatures by Hebert and coworkers almost a decade ago. The concept of barcoding alone is well-known to the public: a series of black bars printed on many commercial products (Universal Product Code), which are used to distinguish different products. Advances made in molecular biology and molecular techniques late 20th century e.g. sequencing technologies, has inspired scientists to apply barcoding concept to all domains of life by using the unique nature of DNA for each single species, in order to generate a comprehensive library of living organisms on the planet earth. Such an ambitious initiative would result in a global DNA barcode database which will be valuable for biological scientists, medical, governmental and legal agencies as a mean of identification. The first initiative for DNA barcoding was funded in Canada and later on several DNA barcoding campaigns came in to the scene. The International Barcode of Life consortium (http://ibol.org/) was established in 2004. It is an international initiative devoted to develop DNA barcoding as a global standard for the identification of biological species. The Consortium for the Barcode of Life (CBOL), an international consortium coordinated from Smithsonian Institute in Washington (USA), was established to promote DNA barcoding, coordinate efforts and generally oversee the standardization process. DNA barcoding is a technique for discriminating species through analysis of sequence data, i. e. short sequences of genetic material in the genome that are unique to that organism are used to identify species mainly through PCR amplification by using primers for the broadest- possible target taxonomic group. The usefulness of DNA barcodes for proper discrimination of species was first demonstrated in animals. A 648 nucleotide base pair length region from the mitochondrial cytochrome c oxidase 1 (CoI) gene was used to identify different animal species; such that, this short sequence has emerged as the standard barcode region for higher animals. The important criteria for barcode loci are effective species-level identification – achieved when interspecific variation exceeds intraspecific –, universality, good sequence quality and coverage. Several global DNA barcoding campaigns have been established to target specific taxonomic groups such as such as plants, fungi, protists, bacteria and different entities of the kingdom animal including fishes, brides, insects, nematodes, mammals etc. In most cases in animals, CoI provides adequate resolution. However, in plants, fungi the substitution rates of this gene are much slower, and scientists are actively searching for barcode genes. For example the nuclear ribosomal Internal Transcribed Spacer (ITS) region has been proposed as universal DNA barcode marker for Fungi by the Fungal Barcoding Consortium published. However, in certain groups of fungi the ITS region fail to discrimination species; such that, secondary barcode loci will be needed for the proper delineation of species in question. One of the most important issues in DNA barcoding is standardization. A DNA barcode is not the same as a DNA sequence. For a barcode, the sequence should stem from a voucher specimen with the voucher being accessible in public collections and the trace files on which the sequences are based should be publically available. The quality and uniformity of data in databases is very crucial for the success of DNA barcodes as a universal molecular identification key. To achieve this goal, a set of guidelines and protocols should be set from collecting species to storing molecular data. The final goal of DNA barcoding project is to create a barcode reference library, where sequence data must be integrated with well characterized taxonomic units. Reference sequences are the core component of the DNA