The Bifidobacteriaceae are the only

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

in the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Bifidobacteriales The Bifidobacteriaceae are the only family of bacteria in the order '' Bifidobacteriales''. According to the 16S rRNA-based LTP release 106 published by 'The All-Species Living Tree' Project, the order Bifidobacteriales is a clade nested withi ...

''. According to the

16S rRNA 16S rRNA may refer to: * 16S ribosomal RNA 16 S ribosomal RNA (or 16 S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome ( SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The g ...

-based LTP release 106 published by

'The All-Species Living Tree' Project The All-Species Living Tree' Project is a collaboration between various academic groups/institutes, such as ARB Project, ARB, SILVA rRNA database project, and List of Prokaryotic names with Standing in Nomenclature, LPSN, with the aim of assembli ...

, the order

is a clade nested within the suborder

Micrococcineae The Micrococcales are an order of bacteria in the phylum Actinomycetota. Phylogeny The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature List of Prokaryotic names with Standing in Nomenclature ...

, also the genus '' Bifidobacterium'' is

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

to the other genera within the family, i.e. the other genera are nested within '' Bifidobacterium''.

Genomics

In a

phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

for the order ''Bifidobacteriales'', based on RpoB, RpoC, and DNA Gyrase B, ''

Gardnerella vaginalis ''Gardnerella vaginalis'' is a species of Gram-variable-staining facultative anaerobic bacteria. The organisms are small (1.0–1.5 μm in diameter) non-spore-forming, nonmotile coccobacilli. Once classified as ''Haemophilus vaginalis'' an ...

'' branches between different '' Bifidobacterium'' species, which makes the genus ''Bifidobacterium'' polyphyletic. The genus could be made

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

if ''G. vaginalis'' were placed within ''Bifidobacterium''. Comparative analysis of aligned protein sequences has led to the discovery of two conserved signature indels which are specific for the order ''Bifidobacteriales''. The first

indel Indel is a molecular biology term for an insertion or deletion of bases in the genome of an organism. It is classified among small genetic variations, measuring from 1 to 10 000 base pairs in length, including insertion and deletion events that ...

, a 1

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

deletion in

ribosomal protein L13 60S ribosomal protein L13 is a protein that in humans is encoded by the ''RPL13'' gene. Function Ribosomes, the organelles that catalyze protein synthesis, consist of a small 40S subunit and a large 60S subunit. Together these subunits are c ...

, is found in all ''Bifidobacteriales'' species and no other '' Actinomycetota'', providing a potential

molecular marker A molecular marker is a molecule, sampled from some source, that gives information about its source. For example, DNA is a molecular marker that gives information about the organism from which it was taken. For another example, some proteins can be ...

for the entire ''Bifidobacteriales'' order. The second indel that has been identified is a 1 amino acid insertion in glucose-6-phosphate dehydrogenase found in all ''Bifidobacterium'' species and ''G. vaginalis'', but not in any other ''Actinomycetota''. This indel is thus characteristic of the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

consisting of ''Bifidobacterium'' species and ''G. vaginalis'' and can be used to distinguish these genera from the rest of the order ''Bifidobacteriales''. 16 conserved signature proteins have also been identified which are unique to the order ''Bifidobacteriales'' and can be used as molecular markers for this order. Additionally, 6 conserved signature proteins which are unique to ''Bifidobacterium'' and ''

Gardnerella ''Gardnerella'' is a genus of Gram-variable-staining facultative anaerobic bacteria. Eponym It is named after Hermann L. Gardner (1912–1982), an American bacteriologist who discovered it in 1955. References

Bifidobacteriales Bacteria ...

'' have been identified, providing further evidence that species from these two genera are closely related and providing molecular markers for the clade consisting of these genera.

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN). The phylogeny is based on whole-genome analysis.

Notes

References

External links

Systema Naturae 2000 / Classification - Family Bifidobacteriaceae
{{Taxonbar, from=Q4904765 Bifidobacteriales Bacteria families Bacteria described in 1997