[The concept of bacterial species]

Prokaryotes are the most abundant living organisms and also most diverse from genetically and metabolically point of view, being responsible for the majority of biogeochemical processes playing the most important role in life cycle on the planet. Considering this, there is a general agreement among taxonomists, that there is a very small number of bacterial species recognized and described today, mostly because of controversial issues concerning bacterial species concept. One of the most accepted approaches, even today, is the polyphasic taxonomy because it is based on diverse information, obtained from classic taxonomy but also from molecular level. The development of new molecular techniques, especially sequencing rRNA genes conducted to an improved concept, that we intended to evaluate in this review, and even more, to reconstruction of group specific phylogenetic tree.