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Chapter 15 : Taxonomy and Classification of Bacteria
The process of species delineation in bacterial systematics has undergone drastic modifications as the species concept evolved in parallel with technical progress. The early classification concept was replaced by theories of so-called natural concepts, which were the phenetic and phylogenetic classifications. In the former, relationships between bacteria were based on the overall similarity of phenotypic and genotypic characteristics. The species is the most important and, at the same time, the central element of bacterial taxonomy. The tree of life, based on comparative small-subunit rRNA studies, comprises three lines of descent that are nowadays referred to as the domains Bacteria, Archaea, and Eucarya. Researchers have reported on the place for 16S rRNA gene sequence analysis and DNA-DNA reassociation in the present species definition in bacteriology. In spite of its limitations, rRNA sequence analysis is now commonly used for the identification of bacteria. The determination of the cell wall composition has traditionally been important for gram-positive bacteria. The majority of bacteria in routine diagnostic laboratories will continue to be identified by classical methods, as these methods are adequate, inexpensive, readily available and easy to handle. The present view of classification reflects the best science of this time. The same was true in the past, when only data from morphological and biochemical analyses were available. The main perspective in bacterial taxonomy is that technological progress will dominate and drastically influence methodology, as it always has.