Phototrophic bacteria (an incoherent group of prokaryotes). A taxonomic versus phylogenetic survey.

In spite of their apparently consistent classical systematic scheme the phototropic bacteria are, as 16S-rRNA oligonucleotide cataloguing and sequencing have shown, deeply split into phylogenetic divisions of very little relationships between one another. Phototrophy as a mode of energy metabolism occurs in the phylogenetic divisions of a) "Gram-positive eubacteria", b) "Cyanobacteria/Chloroplasts", c) "Green Sulfur Bacteria", d) "Chloroflexus and related taxa", and e) "Purple Bacteria and related taxa", i.e. in five of the nine phylogenetic divisions of eubacteria. The arising disagreements are discussed and an attempt is made towards a stepwise reconciliation of taxonomy with phylogeny. The strong and the weak points in the taxonomy of phototrophic eubacteria are pointed out within the existing families. Emphasis is given to areas where taxonomic studies are urgently needed.