3.3 Speciation

Abstract

The process of speciation in bacterial systematics has undergone extensive modification in the past 30 years, and the species concept has evolved in parallel with technical progress. The first classification system in speciation is referred as artificial and used mainly morphological and biochemical criteria to speciate bacteria. This type of classification is monothetic as it is based on a unique set of characteristics that is supposed to be necessary and sufficient to delineate groups. Classification systems can be differentiated in special purpose and general purpose classification systems. The chapter also discusses criteria for species delineation. The criteria used to delineate species have developed in parallel with technology. The early classifications were based on morphology and simple biochemistry, which supplied the available data. When evaluated today, many of these early phenotype-based classifications generated extremely heterogeneous assemblages of bacteria. Individual species were characterized by a common set of phenotypic characters and differed from other species in one or a few characters that were considered important. Lastly, the chapter explains the polyphasic species concept.