It is a label put before the name of a bacterium which cannot be grown on an agar plate or in any other bacteriology culture. An example would be "Candidatus Phytoplasma allocasuarinae". Candidatus status may be used when a species or genus is well studied but cannot be cultured. Nowadays much information is got by 16S ribosomal RNA sequence analysis.
For correct publication of a species, bacteria must be isolated, cultured, described, and deposited in a bacteriology culture collection. However, some bacteria require special tissue culture conditions and cannot be maintained in Bacteriology Culture Collections. This includes bacteria which live inside other organisms or cells. These include obligately intracellular pathogens and endosymbionts, insect symbionts, and populations from oceans or sludge.
In 1994, Murray and Schleifer published a taxonomic note. 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 and Evolutionary Microbiology.
- Latin for candidate of Roman office, named after the white gown worn by Roman senators
- Notice the Candidatus is italicised but the name is not.
- Murray R.G.E. and Schleifer K.H. 1994 Taxonomic notes: a proposal for recording the properties of putative taxa of procaryotes. Int. J. Syst. Bacteriol. 44, 174-176
- Murray R.G.E. and Schleifer K.H. 1995 Taxonomic note: Implementation of the provisional status Candidatus for incompletely described procaryotes Archived 2009-08-01 at the Wayback Machine; Int. J. Syst. Bacteriol. 45, 186-187
- Judicial Commission of the International Committee on Systematic Bacteriology. Minutes of the Meetings, 2 and 6 July 1994; Int. J. Syst. Bacteriol., 1995, 45, 195-196.
- 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.