Candidatus in scientific classification is a word that is placed before the genus and species name of a bacterium that has not been formally named. An example would be "Candidatus Phytoplasma allocasuarinae". This naming system is commonly used when a species or genus is well characterised, but the organism has not yet been cultured.

History

In 1994, Murray and Schleifer published a taxonomic note in which they recommended that the new category of indefinite rank (Candidatus) be established for certain putative taxa that could not be described in sufficient detail to warrant establishment of a new taxon. It was also recommended that a Candidatus list should be established in the International Journal of Systematic Bacteriology (now International Journal of Systematic and Evolutionary Microbiology ).

The taxonomic note proposing the establishment of the provisional status Candidatus for incompletely described procaryotes was published in the January 1995 issue of the IJSB. According to this note, the category Candidatus should be used for describing procaryotic entities for which more than a DNA sequence is available but for which characteristics required for description according to the Bacteriological Code are lacking. In addition to genomic information such as sequences, all information, including structural, metabolic, and reproductive features should be included in the description.

Usage

According to the "Ad Hoc Committee for the re-evaluation of the species definition in bacteriology", microbiologists are encouraged to use the "Candidatus" concept for well characterised but as yet uncultured organisms.

The names included in the category Candidatus are usually written as follows: Candidatus (in italics), the subsequent name(s) in roman type (with an initial cap for the genus name) and the entire name in quotation marks. For example, "Candidatus Phytoplasma", "Candidatus Phytoplasma allocasuarinae".

According to the "IRPCM Phytoplasma/Spiroplasma Working Team - Phytoplasma taxonomy group" the abbreviation for Candidatus should be Ca..

References

MURRAY (R.G.E.) and SCHLEIFER (K.H.): Taxonomic notes: a proposal for recording the properties of putative taxa of procaryotes. Int. J. Syst. Bacteriol., 1994, 44, 174-176.

JUDICIAL COMMISSION OF THE INTERNATIONAL COMMITTEE ON SYSTEMATIC BACTERIOLOGY: Minutes of the meetings, 2 and 6 July 1994, Prague, Czech Republic. Int. J. Syst. Bacteriol., 1995, 45, 195-196.

MURRAY (R.G.E.) and STACKEBRANDT (E.): Taxonomic Note: implementation of the provisional status Candidatus for incompletely described procaryotes. Int. J. Syst. Bacteriol., 1995, 45, 186-187.

JUDICIAL COMMISSION OF THE INTERNATIONAL COMMITTEE ON SYSTEMATIC BACTERIOLOGY: VIIth International Congress of Microbiology and Applied Bacteriology. Minutes of the meetings, 17 and 22 August 1996, Jerusalem, Israel. Int. J. Syst. Bacteriol., 1997, 47, 240-241.

INTERNATIONAL COMMITTEE ON SYSTEMATIC BACTERIOLOGY: VIIth International Congress of Microbiology and Applied Bacteriology. Minutes of the meetings, 17, 18, and 22 August 1996, Jerusalem, Israel. Int. J. Syst. Bacteriol., 1997, 47, 597-600.

DE VOS (P.), TRÜPER (H.G.) and TINDALL (B.J.): Judicial Commission of the International Committee on Systematics of Prokaryotes Xth International (IUMS) Congress of Bacteriology and Applied Microbiology. Minutes of the meetings, 28, 29 and 31 July and 1 August 2002, Paris, France. Int. J. Syst. Evol. Microbiol., 2005, 55, 525-532.

STACKEBRANDT (E.), FREDERIKSEN (W.), GARRITY (G.M.), GRIMONT (P.A.D.), KÄMPFER (P.), MAIDEN (M.C.J.), NESME (X.), ROSSELLO-MORA (R.), SWINGS (J.), TRÜPER (H.G.), VAUTERIN (L.), WARD (A.C.) and WHITMAN (W.B.): Report of the ad hoc committee for the re-evaluation of the species definition in bacteriology. Int. J. Syst. Evol. Microbiol., 2002, 52, 1043-1047.

The IRPCM Phytoplasma/Spiroplasma Working Team - Phytoplasma taxonomy group: 'Candidatus Phytoplasma', a taxon for the wall-less, non-helical prokaryotes that colonize plant phloem and insects. Int. J. Syst. Evol. Microbiol., 2004, 54, 1243-1255.