A multi-gene approach in the systematics of the phototrophic purple sulfur bacteria genera Marichromatium and Allochromatium with description of the new species Allochromatium humboldtianum and the new biotype Marichromatium gracile biotype thermosulfidiphilum.

In the present thesis two genera of the photosynthetic Purple Sulfur Bacteria (PSB) of the family Chromatiaceae are revised by molecular techniques which include extensive DNA-DNA hybridization (DDH) studies and a multi-gene analysis. Traditionally, species of PSB have been described based on some easily recognizable phenotypic properties and separated in two families the Chromatiaceae and Ectothiorhosdopiraceae. Within the Chromatiaceae the genus Chromatium was also separated in several genera being the most important the genera Marichromatium and Allochromatium. Type species within each genus does not exhibit remarkable phenotypic properties and phylogenetically they are difficult to resolve using a high conserved loci such as the 16S rRNA. In the present study the analysis of the concatenated protein-coding gene sequences for the genera Marichromatium (4331 bp) and Allochromatium (4427 bp) allowed the separation of all examined strains within each genus in several independent clusters of phylotypes that in many cases reflect previous species circumscription based on phenotypic analysis. Thus, MLSA approach could be used as a valuable tool for separating closely related strains.