The Richness of Prokaryotic Diversity: There Must Be a Species Somewhere

The rapidly increasing number of potentially novel species, combined with the methodologically laborious polyphasic approach used in bacterial systematics, makes identification and, consequently, the description of novel taxa a highly demanding discipline. The number of new descriptions of about 200 species a year can apparently not be expanded significantly but new isolation procedures and renewed interest in working with bacteria rather than with DNA clones provide microbiologists with a broad range of different pheno- and genotypes. It seems obvious that some of the worldwide acknowledged techniques will not be continued but the question which methods will be used in the future is still open. At present, DNA-DNA reassociation is the final arbiter for the taxon »species«, but the limitations of these techniques, which are subject to significant errors, are well known. On the other side of the range of molecular techniques stands a whole genome sequencing that demonstrates the evolutionary events which lead to differences in DNA, such as point mutations, insertions and deletions, DNA acquisition and loss, recombination, gene loss and formation of pseudogenes. Each of these evolutionary events has an effect on DNA-DNA reassociation similarity, which, however, cannot be tested by the reassociation approaches used. Further, DNA pairing does not allow the establishment of a cumulative database because the hybridization parameters change from laboratory to laboratory and reference organisms need to be included in each experiment. This communication reports on the development of ideas that may change the paradigm of the present concept of artificial, arbitrary and pragmatic species into a species definition, driven by insights into population genetics