Proposal to emend Rules 50 a and 50 b of the International Code of Nomenclature of Prokaryotes

Rules 50a and 50b of the International Code of Nomenclature of Prokaryotes respectively regulate the elevation of a subspecies to the rank of a species and the lowering of a species to the rank of subspecies. The Code does not indicate that the resulting new names must be considered new combinations, as the cases described in Rules 50a and 50b are not covered by Rule 34a. Based on the rules of the Code, new combination events are applicable only at the identical rank, and therefore new combination events and new species/subspecies events are mutually exclusive. In spite of this there have been at least 44 cases in which the new names were described as comb. nov. during elevation in rank from subspecies to species and at least 30 such cases during lowering in rank from species to subspecies. To prevent confusion in the future we propose adding notes to Rules 50a and 50b to clarify the issue. According to Rule 34a of the International Code of Nomenclature of Prokaryotes [1] and the earlier version the International Code of Bacterial Nomenclature [2], when an author transfers a species to another genus, or a subspecies to another species, then the author who makes the transfer should indicate the formation of the new combination by the addition to the citation of the abbreviation ‘comb. nov.’ (combinatio nova). The original name is referred to as the basonym. Based on Rule 34a, events in which a subspecies is elevated in rank to a species (Rule 50a) or a species is lowered in rank to a subspecies (Rule 50b) cannot be new combination events: new combination events are applicable only at the identical rank. In spite of this, there have been many such cases in which ‘comb. nov.’ was added and basonyms were assigned. Table 1 lists 45 cases in which subspecies were elevated to the rank of species as ‘comb. nov.’ and 30 cases in which species were lowered to the rank of subspecies as ‘comb. nov.’. These lists are not necessarily exhaustive. Because of the widespread confusion about the use of the concept of combinatio nova as a result of incorrect interpretation of Rule 34a and its application in cases a subspecies is elevated in rank to a species or a species is lowered in rank to a subspecies, in spite of the fact that new combination events are applicable only at the identical rank, we propose adding Notes to Rules 50a and 50b of the Code to clarify the matter. We propose that these changes be non-retroactive. The proposed emended Rules are as follows (newly added text printed in boldface): RULE 50A When a subspecies is elevated in rank to a species, the subspecific epithet in the name of the subspecies must be used as the specific epithet of the name of the species unless the resulting combination is illegitimate. Example: Campylobacter pylori subsp. mustelae Fox et al. 1988 becomes Campylobacter mustelae (Fox et al. 1988) Fox et al. 1989. Note. Based on Rule 34a, elevation of a subspecies to the rank of species does not create a new combination. New combination events are applicable only at the identical rank. RULE 50B When a species is lowered in rank to a subspecies, the specific epithet in the name of the species must be used as the subspecific epithet of the name of the subspecies unless the resulting combination is illegitimate. Example: Bifidobacterium globosum (ex Scardovi and Trovatelli 1969) Biavati et al. 1982 becomes Bifidobacterium pseudolongum subsp. globosum (Biavati et al. 1982) Yaeshima et al. 1992. Author affiliations: The Institute of Life Sciences, The Hebrew University of Jerusalem, The Edmond J. Safra Campus, 9190401 Jerusalem, Israel; Department of Microbiology & Molecular Genetics, Biomedical Physical Sciences, Michigan State University, East Lansing, MI 48824-4320, USA. *Correspondence: Aharon Oren, aharon.oren@mail.huji.ac.il

Based on Rule 34a, events in which a subspecies is elevated in rank to a species (Rule 50a) or a species is lowered in rank to a subspecies (Rule 50b) cannot be new combination events: new combination events are applicable only at the identical rank.In spite of this, there have been many such cases in which 'comb.nov.' was added and basonyms were assigned.Table 1 lists 45 cases in which subspecies were elevated to the rank of species as 'comb.nov.' and 30 cases in which species were lowered to the rank of subspecies as 'comb.nov.'.These lists are not necessarily exhaustive.
Because of the widespread confusion about the use of the concept of combinatio nova as a result of incorrect interpretation of Rule 34a and its application in cases a subspecies is elevated in rank to a species or a species is lowered in rank to a subspecies, in spite of the fact that new combination events are applicable only at the identical rank, we propose adding Notes to Rules 50a and 50b of the Code to clarify the matter.We propose that these changes be non-retroactive.
The proposed emended Rules are as follows (newly added text printed in boldface):

RULE 50A
When a subspecies is elevated in rank to a species, the subspecific epithet in the name of the subspecies must be used as the specific epithet of the name of the species unless the resulting combination is illegitimate.

RULE 50B
When a species is lowered in rank to a subspecies, the specific epithet in the name of the species must be used as the subspecific epithet of the name of the subspecies unless the resulting combination is illegitimate.*A footnote was added to the Notification List for the issue of the IJSEM in which the taxon was published [19] to explain that the newly proposed name is illegitimate at it contravenes Rule 34a and 50a of the International Code of Nomenclature of Prokaryotes.†This name was effectively but not validly published.‡The List Editor added the following correction: In the effective publication, Enterobacter cloacae subsp.cloacae is erroneously proposed as a new combination [51].§The addition comb.nov.was deleted in the Validation List [65].

Table 1 .
Cases in which new combinations were proposed when subspecies were elevated in rank to species or species were lowered to the rank of subspecies or subspecies, thereby contravening Rules 34a, 50a and 50b of the Prokaryotic Code Subspecies elevated in rank to species IP: 54.70.40.11On: Wed, 17 Oct 2018 14:07:53

Table 1 .
cont.Note.Based on Rule 34a, lowering a species to the rank of subspecies does not create a new combination.New combination events are applicable only at the identical rank.