The genus Allochromatium (Chromatiales Chromatiaceae) revisited: a study on its intragenic structure based on multilocus sequence analysis (MLSA) and DNA-DNA hybridization (DDH)

In this study, the taxonomic status of anoxygenic photosynthetic bacteria belonging to the genus Allochromatium is revisited. The inter- and intraspecies relationship of seven Allochromatium strains, including a set of well described type strains, were examined by DNA-DNA hybridization (DDH) and multilocus sequence analysis (MLSA) using segments of seven protein-coding genes. The re-sequencing of the 16S rRNA, the internal transcriber spacer (ITS), multi-gene analysis and DDH comparison indicated that both type strains Allochromatium vinosum DSM 180^T and Allochromatium minutissimum DSM 1376^T are closely related to each other forming an independent cluster together with the strains A. vinosum DSM 183 and DSM 1686. The internal comparison of members of this A. vinosum phylogroup showed values of DDH relatedness above 80% and concatenated sequence similarities (4744 bp) above 98%. In contrast, the MLSA scheme has identified A. vinosum strain BH-2 as a separate lineage. Strain BH-2 was first classified as a member of the species A. vinosum based on DDH comparison. However, this strain showed the lowest similarity values of the 16S rRNA gene and concatenated sequences, as well as amino acid identity (AAI) when compared to other Allochromatium strains, suggesting that strain BH-2 may represent a new species.