ABSTRACT
Prokaryotes represent a most diverse biomass on the Earth. It has been estimated that the number of bacterial taxa in oceans may approach 2 million (or 160/mL), in soil at least 4 million (or 6,400-38,000/gm), and in the atmosphere at least 4 million [1]. This estimation puts the total number of bacterial species in the order of 10 million and perhaps up to a billion. In contrast, there are probably between 10 and 30 million of animal species, the vast majority of which are insects. At the moment, the number of scientifi cally recognized animal species is about 1,250,000, and the number of recognized plant species amounts to almost 300,000. Given that the emergence and evolution of microbial organisms greatly preceded plants and animals, and that bacteria have relatively short generation times and are adapted to fi ne-scale microenvironments in all ecosystems, it is surprising that the total number of characterized bacterial species only stands at about 5000.
