Occurrence, phylogeny and evolution of ribulose-1,5-bisphosphate carboxylase/oxygenase genes in obligately chemolithoautotrophic sulfur-oxidizing bacteria of the genera Thiomicrospira and Thioalkalimicrobium.

The occurrence of the different genes encoding ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), the key enzyme of the Calvin-Benson-Bassham cycle of autotrophic CO(2) fixation, was investigated in the members of the genus Thiomicrospira and the relative genus Thioalkalimicrobium, all obligately chemolithoautotrophic sulfur-oxidizing Gammaproteobacteria. The cbbL gene encoding the 'green-like' form I RubisCO large subunit was found in all analysed species, while the cbbM gene encoding form II RubisCO was present only in Thiomicrospira species. Furthermore, species belonging to the Thiomicrospira crunogena 16S rRNA-based phylogenetic cluster also possessed two genes of green-like form I RubisCO, cbbL-1 and cbbL-2. Both 16S-rRNA- and cbbL-based phylogenies of the Thiomicrospira-Thioalkalimicrobium-Hydrogenovibrio group were congruent, thus supporting its monophyletic origin. On the other hand, it also supports the necessity for taxonomy reorganization of this group into a new family with four genera.