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Classification of the Bacteria: Traditional
Encyclopedia of Food Microbiology (2nd Edition)
Academic Press
Lugar: Londres; Año: 2013; p. 169 - 173
Taxonomy is a subdiscipline of biology that deals with classification of living beings. Classification involves characterizing, naming, and grouping organisms according to their natural relationships. Systematics relates taxonomy with phylogenetics, which studies the relation among the sequences of organisms, like a phylogenetic tree (see Bacteria: Classification of the Bacteria ? Phylogenetic Approach). Bacterial taxonomy has changed profoundly during recent decades, incorporating novel identification methods and additional criteria to describenewspecies.This ?polyphasic taxonomic approach? involves the combination of phenotypic, genotypic, and phylogenetic techniques that are necessary to identify and describe bacteria.The phenotypic study includes morphological, metabolic, physiological, and chemical characteristics of the cell, whereas genotypic analysis compares the bacterial genome. With these two techniques, organisms are grouped according to their similarities. These studies are complemented with phylogenetics, which studies the parental relation among microorganisms. Polyphasic taxonomy also considers the importance of the habitat of each bacterium and its ecology. Traditional bacterial taxonomy provides useful identification methods based on phenotypic characteristics. The prominent role it used to play in the past is now decreasing, however, due to the easiness to obtain particular DNA sequences. These advances in molecular techniques are the cause for the decline in importance of the traditional approach of taxonomy because its reliability does not meet modern standards. In fact, newly developed genetic techniques allow for microbial identification without the need to culture them, as many microorganisms can be present in their noncultural state (see Identification Methods: Culture-Independent Techniques). In any study involvingmicroorganisms, reliable identification of isolates is absolutely essential. Identification is possible only when coherent bacterial classification is available. Bacteria are classified into a hierarchy of ranks (from high to low): domain, phylum, class, order, family, genus, species, and subspecies.