Taxonomic rearrangements of the genera Thiocapsa and Amoebobacter on the basis of 16S rDNA sequence analyses, and description of Thiolamprovum gen. nov.

This study used 16S rDNA sequence analysis to reorganize the taxonomic classification of phototrophic purple sulfur bacteria in the genera Thiocapsa and Amoebobacter within the family Chromatiaceae. The researchers sequenced 16S rRNA genes from all available type strains and additional isolates, then constructed phylogenetic trees based on sequence similarity and evolutionary distances. Analysis revealed that strains previously classified as Thiocapsa and Amoebobacter clustered into two major groups. The close relationship between Thiocapsa roseopersicina, Amoebobacter roseus, and Amoebobacter pendens (93.9-96% similarity) indicated they belonged to a single genus, which should be Thiocapsa. In contrast, Amoebobacter purpureus and A. pedioformis showed only 88.9% sequence similarity to other members and to each other, warranting separate generic status. The authors propose maintaining an emended genus Thiocapsa with three species, redefining Amoebobacter with A. purpureus as the type species, and creating a novel genus Thiolamprovum for the transfer of A. pedioformis. Two species, T. pfennigii and T. halophila, were found phylogenetically distinct and removed from Thiocapsa pending further clarification.

Key findings

• Thiocapsa roseopersicina, Amoebobacter roseus, and A. pendens form a closely related group (93.9-96% sequence similarity) and should be consolidated within genus Thiocapsa with three recognized species
• Amoebobacter purpureus and A. pedioformis are phylogenetically distinct from the T. roseopersicina group and warrant separate generic status
• Gas vesicle presence/absence is not taxonomically relevant at the genus level for these purple sulfur bacteria
• A novel genus Thiolamprovum is described for A. pedioformis, with A. purpureus designated as the new type species for emended Amoebobacter
• Thiocapsa pfennigii and T. halophila are phylogenetically distant from T. roseopersicina and should be removed from the genus pending further taxonomic clarification