Transfer of the bacteriochlorophyll b-containing phototrophic bacteria Rhodopseudomonas viridis and Rhodopseudomonas sulfoviridis to the genus Blastochloris gen. nov

This study reclassifies two bacteriochlorophyll b-producing phototrophic bacteria previously assigned to Rhodopseudomonas into a new genus, Blastochloris. The researcher analyzed 16S rRNA gene sequences and genomic DNA-DNA hybridization for Rhodopseudomonas viridis and Rhodopseudomonas sulfoviridis, comparing them with related species. The 16S rDNA sequences showed 98.7% similarity between the two species, while DNA hybridization revealed 38% relatedness, indicating they are closely related but distinct species. Phylogenetic analysis demonstrated that both organisms form a tight cluster with the genus Rhodoplanes as a sister group within the alpha-2 subgroup of Proteobacteria, and they are phylogenetically distant from Rhodopseudomonas palustris. Based on this molecular and phenotypic evidence, the author proposes transferring these two species to the new genus Blastochloris as Blastochloris viridis and Blastochloris sulfoviridis. This reclassification is supported by the unique feature that these are the only bacteriochlorophyll b-producing species among purple nonsulfur bacteria, and reflects their distinct evolutionary lineage within photosynthetic bacteria.

Key findings

• 16S rRNA gene sequences showed 98.7% similarity between R. viridis and R. sulfoviridis but only 38% genomic DNA hybridization, confirming they are different species within a single genus
• Phylogenetic analysis positioned both species as a distinct clade with Rhodoplanes as the closest relative within the alpha-2 Proteobacteria subgroup, separate from R. palustris
• The two bacteriochlorophyll b-producing species form a monophyletic group unique among all recognized purple nonsulfur bacteria genera
• The new genus Blastochloris is proposed to accommodate these bacteriochlorophyll b-producing budding phototrophic bacteria with genomic DNA G+C content of 66-71 mol%