Candidatus is in scientific classification a component of the taxonomic name for a bacterium that cannot be maintained in a Bacteriology Culture Collection. It is an interim taxonomic status for noncultivable organisms. An example would be "Candidatus Phytoplasma

Phytoplasma

Phytoplasma are specialised bacteria that are obligate parasites of plant phloem tissue and transmitting insects . They were first discovered by scientists in 1967 and were named mycoplasma-like organisms or MLOs. They cannot be cultured in vitro in cell-free media...

 allocasuarinae". Candidatus status may be used when a species or genus is well characterised but unculturable. Nowadays much information is obtained by 16S ribosomal RNA

16S ribosomal RNA

16S ribosomal RNA is a component of the 30S subunit of prokaryotic ribosomes. It is approximately 1.5kb in length...

 sequence analysis.

History

For valid publication of a species, bacteria must be isolated, cultured, described, and deposited in a Bacteriology Culture Collection. However, some bacteria require special culture conditions and cannot be maintained in Bacteriology Culture Collections. These include obligately intracellular pathogens and endosymbionts, insect symbionts, and populations from oceans or sludge. 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

Taxon

|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

. 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

International Journal of Systematic and Evolutionary Microbiology

The International Journal of Systematic and Evolutionary Microbiology is a peer-reviewed scientific journal in the field of microbial systematics, first published in 1951...

).

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

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 sequence is available but for which characteristics required for description according to the Bacteriological Code

International Code of Nomenclature of Bacteria

The International Code of Nomenclature of Bacteria or Bacteriological Code governs the scientific names for bacteria, including Archaea. It denotes the rules for naming taxa of bacteria, according to their relative rank...

 are lacking. In addition to genomic information such as sequences, all information, including structural, metabolic, and reproductive features should be included in the description.

Newly proposed culturable bacteria must be deposited in at least two publicly accessible culture collections in different countries (Euzéby and Tindall, 2004).

Usage

According to the "Ad Hoc Committee for the re-evaluation of the species definition in bacteriology

Bacteriology

Bacteriology is the study of bacteria. This subdivision of microbiology involves the identification, classification, and characterization of bacterial species...

", microbiologist

Microbiologist

A microbiologist is a scientist who works in the field of microbiology. Microbiologists study organisms called microbes. Microbes can take the form of bacteria, viruses, fungi, and protists...

s 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

Spiroplasma

Spiroplasma is a genus of Mollicutes, a group of small bacteria without cell walls. Spiroplasma shares the simple metabolism, parasitic lifestyle, fried-egg colony morphology and small genome of other Mollicutes, but has a distinctive helical morphology, unlike Mycoplasma. It has a spiral shape...

Working Team - Phytoplasma taxonomy group" the abbreviation for Candidatus should be Ca..