Commentary on the proposed Section 10 amendments to the International Code of Nomenclature of Prokaryotes regarding Candidatus names.

Amendments were proposed to the International Code of Nomenclature of Prokaryotes (ICNP) in January [Arahal et al. (2024) Int. J Syst. Evol. Microbiol. 74: 006188] that would cause major changes in the treatment of Candidatus names. The amendments introduce Section 10 to name taxa whose names cannot be validly published under the ICNP because of the absence of type strains. This section creates a parallel 'pro-nomenclature' and formalizes alternative material which could serve as nomenclatural types. When conspecific isolates of taxa with Candidatus names are deposited in culture collections as type strains, the names can be validly published, and it is required that the same Candidatus name be used. While the amendments are promoted to provide stable names and rules of nomenclature for uncultivated taxa, the system is deeply flawed. It removes the permanent association between names and types, which will make the meaning of names imprecise and ambiguous. It creates 'pro-nomenclature', which is confusing and unnecessary. Since many taxa which cannot be validly named under the ICNP can already be named under the SeqCode, it duplicates and creates overlap with an established nomenclatural system without providing tangible benefits. As the SeqCode recognizes names formed under the ICNP, the ICNP should recognize names formed under the SeqCode as they have done for the Cyanobacteria named under the International Code of Nomenclature for algae, fungi and plants (ICN). For these reasons, we urge the members of the International Committee of Systematics of Prokaryotes (ICSP) to reject these amendments.