Genomic and genetic sequence information of strains assigned to the genus reveal the great heterogeneity of the group and identify strain DSM 123 as the authentic type strain of this species.

The genus , containing purple nonsulfur photosynthetic Proteobacteria, has a number of strains that belong to different species, although many of them are collectively called . The type species and closely related species are the focus of this paper. The comparison of available genome sequences indicate that the following species are well recognized: (strains ATH 2.1.6=DSM 123=NBRC 100419 and BisB5), (strains R1, DSM 126, CGA009, ATH 2.1.37, Eli 1980, ATCC 17001 and TIE1), JA575 and JCM 11668. Other strains for which genome sequences are available are distinct from these four species. Evidence is presented that strain ATH 2.1.6-KCM as obtained directly from the van Niel collection by one of us (T.E.M.) is identical to the DSMZ deposit DSM 123 of ATH 2.1.6, but not to the deposit at ATCC 17001. The amino acid sequences of the cytochromes C2 and C556 from strain ATH 2.1.6-KCM are in complete agreement with the translated genome sequences of DSM 123. In addition, the 16S rRNA gene sequence of NBRC 100419 completely matches that of strain DSM 123. In conclusion, the type strain of ATH 2.1.6 is correctly represented by DSM 123 and NBRC 100419. However, the deposit at ATCC 17001 has properties that do not conform with properties of authentic , but rather indicate that this is a strain of . The previously suggested assignment of the type strain of DSM 123 to the new species was incorrect because strain DSM 123 is the authentic type strain of .