This letter addresses taxonomic nomenclature issues surrounding Rhodospirillum centenum, a non-sulfur purple photosynthetic bacterium isolated in 1987. The organism exhibits remarkable properties including cyst formation, oxygen-tolerant photopigment production, phototactic behavior, and a phytochrome-like protein. Five years after the original publication, researchers proposed renaming it Rhodocista centenaria based primarily on 16S rRNA sequence data. The authors argue this renaming violates basic nomenclatural principles by creating an unnecessary monotypic genus without compelling biological justification. They contend that 16S rRNA sequences alone are insufficient for major taxonomic revisions, noting that horizontal gene transfer complicates phylogenetic interpretation. The authors criticize the validation process that assigned both names identical priority numbers and emphasize that nomenclatural stability should prevail. They advocate using common sense in accepting the original designation Rhodospirillum centenum and highlight broader problems with recent bacterial reclassifications based on limited molecular data. The letter reinforces that phenotypic characteristics and evolutionary understanding require multiple approaches beyond single-gene sequences.

Key findings

• Rhodospirillum centenum displays unusual characteristics including cyst formation, oxygen-tolerant photosynthesis, and phototactic behavior in colonies, distinguishing it as a remarkable experimental organism.
• The proposed renaming to Rhodocista centenaria violates International Code of Nomenclature principles by creating a monotypic genus based on trivial 16S rRNA sequence differences without compelling biological justification.
• 16S rRNA sequences alone are insufficient for defining bacterial taxa; horizontal gene transfer and phenotypic properties must be considered for meaningful taxonomic decisions.
• The validation process assigned identical priority numbers to both the original and proposed names, creating nomenclatural ambiguity contrary to Code principles of stability and clarity.
• Multiple molecular approaches and phenotypic evidence are essential for understanding bacterial evolution, not single-gene phylogenies.