DNA Barcoding: a new tool with wide array of applications

dna barcoding is a new term introduced in toscientific literatures by hebert and coworkers almosta decade ago (1). the concept of barcoding alone iswell-known to the public: a series of black barsprinted on many commercial products (1-3) (universalproduct code), which are used to distinguishdifferent products. advances made in molecularbiology and molecular techniques late 20th centurye.g. sequencing technologies, has inspired scientiststo apply barcoding concept to all domains of life byusing the unique nature of dna for each singlespecies, in order to generate a comprehensive libraryof living organisms on the planet earth (2, 6). such anambitious initiative would result in a global dnabarcode database which will be valuable forbiological scientists, medical, governmental and legalagencies as a mean of identification (1). the firstinitiative for dna barcoding was funded in canadaand later on several dna barcoding campaigns camein to the scene. the international barcode of lifeconsortium (http://ibol.org/) was established in 2004.it is an international initiative devoted to developdna barcoding as a global standard for theidentification of biological species. the consortiumfor the barcode of life (cbol), an internationalconsortium coordinated from smithsonian institute inwashington (usa), was established to promote dnabarcoding, coordinate efforts and generally overseethe standardization process (6). dna barcoding is atechnique for discriminating species through analysisof sequence data, i. e. short sequences of geneticmaterial in the genome that are unique to thatorganism are used to identify species mainly throughpcr amplification by using primers for the broadestpossibletarget taxonomic group (1-3, 5-6). theusefulness of dna barcodes for proper discriminationof species was first demonstrated in animals. a 648nucleotide base pair length region from themitochondrial cytochrome c oxidase 1 (coi) genewas used to identify different animal species; suchthat, this short sequence has emerged as the standardbarcode region for higher animals (3, 7). the importantcriteria for barcode loci are effective species-levelidentification– chieved when inter specific variationexceeds intraspecific –, universality, good sequencequality and coverage. several global dna barcodingcampaigns have been established to target specifictaxonomic groups such as plants, fungi, protists,bacteria and different entities of the kingdom animalincluding fishes, brides, insects, nematodes, mammalsetc (1, 6). in most cases in animals, coi providesadequate resolution. however, in plants, fungi thesubstitution rates of this gene are much slower, andscientists are actively searching for barcode genes(6). for example the nuclear ribosomal internaltranscribed spacer (its) region has been proposedas universal dna barcode marker for fungi by thefungal barcoding consortium published. however,in certain groups of fungi the its region fail todiscrimination species; such that, secondary barcodeloci will be needed for the proper delineation ofspecies in question (5).one of the most important issues in dna barcodingis standardization. a dna barcode is not the same asa dna sequence. for a barcode, the sequence shouldstem from a voucher specimen with the voucherbeing accessible in public collections and the tracefiles on which the sequences are based should bepublically available (1, 4). the quality and uniformityof data in databases is very crucial for the success ofdna barcodes as a universal molecular identificationkey. to achieve this goal, a set of guidelines andprotocols should be set from collecting species tostoring molecular data. the final goal of dnabarcoding project is to create a barcode referencelibrary, where sequence data must be integrated withwell characterized taxonomic units (1, 4, 6). referencesequences are the core component of the dnabarcoding initiative i. e. the reliability of librarydepends on the quality of the voucher specimensfrom which reference sequences are obtained. whenthe voucher specimens are characterized and verifiedby expert taxonomists; then, newly generated sequencescan be easily compared to the library (1, 6). eventually,a compiled public library of sequences linked tonamed specimens together with faster and cheapersequencing will make dna barcoding increasinglyuseful.the primary aim of dna barcoding technique is toprovide a reliable, cost-effective and accessiblesolution to the problem of species identification inorder to obtain a better taxonomic resolution compareto morphological approaches, by allowing even nonspecialiststo identify species in question. with theaid of dna barcode, a species can be identifiedbased on a little amount of dna extracted from anybiological material (tiny amount of tissue, blood,from seeds, or from sterile, juvenile or fragmentarymaterials) when morphological identification isdifficult or even impossible (1, 5, 6). this techniquewill be useful in many ways: rapid and accurateidentification of harmful microorganisms for humanin medical, governmental and legal agencies, studyingextinct species, discriminating possible cryptic species,identifying immature specimens and resolving adultand larval stages within the same species and evencontrolling the identity of food of animal and/orvegetal origin, e.g. fishes for sale in supermarkets (1,6).