The lactic acid bacteria were chosen
to illustrate the problems that occur if settled phenotypic classification schemes do not corroborate phylogenetic insights
based on rRNA sequencing. The presumed causes of confusion are the large number of species in, e.g., the genus Lactobacillus, which are difficult to discriminate with a limited number of phenotypic tests, and the over reliance on morphological
and biochemical characteristics. For the family Comamonadaceae, polyphasic analysis led to a transition type of taxonomy
in which a compromise was formulated on the basis of the
results at hand. It is an example of a family exclusively delineated by using DNA-rRNA hybridization data and in which
phenotypic coherence had a major impact on the delineation
of genera and species. It represents a biochemical very diverse group of bacteria, which form a tight phylogenetic cluster.