*Article* **Genomic Comparison, Phylogeny and Taxonomic Reevaluation of the** *Ectothiorhodospiraceae* **and Description of** *Halorhodospiraceae* **fam. nov. and** *Halochlorospira* **gen. nov.**

**Johannes F. Imhoff 1,\* , John A. Kyndt <sup>2</sup> and Terrance E. Meyer <sup>3</sup>**


**Abstract:** The *Ectothiorhodospiraceae* family represents purple sulfur bacteria of the *Gammaproteobacteria* found primarily in alkaline soda lakes of moderate to extremely high salinity. The main microscopically visible characteristic separating them from the *Chromatiaceae* is the excretion of the intermediate elemental sulfur formed during oxidation of sulfide prior to complete oxidation to sulfate rather than storing it in the periplasm. We present a comparative study of 38 genomes of all species of phototrophic *Ectothiorhodospiraceae*. We also include a comparison with those chemotrophic bacteria that have been assigned to the family previously and critically reevaluate this assignment. The data demonstrate the separation of *Halorhodospira* species in a major phylogenetic branch distant from other *Ectothiorhodospiraceae* and support their separation into a new family, for which the name *Halorhodospiraceae* fam. nov. is proposed. In addition, the green-colored, bacteriochlorophyll-containing species *Halorhodospira halochloris* and *Halorhodospira abdelmalekii* were transferred to the new genus *Halochlorospira* gen. nov. of this family. The data also enable classification of several so far unclassified isolates and support the separation of *Ectothiorhodospira shaposhnikovii* and *Ect. vacuolata* as well as *Ect. mobilis* and *Ect. marismortui* as distinct species.

**Keywords:** purple sulfur bacteria; genomic phylogeny; *Ectothiorhodospiraceae*; *Halorhodospiraceae*; new family and genus
