Editing Streptococcus (section)

==Molecular taxonomy and phylogenetics==
[[File:Streptococcus phylogenetic tree.png|thumb|Phylogenetic tree of ''Streptococcus'' species, based on data from PATRIC.<ref>{{cite web |title=Bacteria-Firmicutes-Bacilli-Lactobacillales-Streptococcaceae-Streptococcus |url=https://www.patricbrc.org/view/Taxonomy/1301#view_tab=phylogeny |website=PATRIC, University of Chicago |access-date=12 December 2014}}</ref> 16S groups are indicated by brackets and their key members are highlighted in red.]]
Streptococci have been divided into six groups on the basis of their [[16S ribosomal RNA|16S]] rDNA sequences: ''S. anginosus, S. gallolyticus, S. mitis, S. mutans, S. pyogenes'' and ''S. salivarius''.<ref name=Kawamura1995>{{cite journal | vauthors = Kawamura Y, Hou XG, Sultana F, Miura H, Ezaki T | title = Determination of 16S rRNA sequences of Streptococcus mitis and Streptococcus gordonii and phylogenetic relationships among members of the genus Streptococcus | journal = International Journal of Systematic Bacteriology | volume = 45 | issue = 2 | pages = 406–408 | date = April 1995 | pmid = 7537076 | doi = 10.1099/00207713-45-2-406 | doi-access = free }}</ref> The 16S groups have been confirmed by whole genome sequencing (see figure). The important pathogens ''S. pneumoniae'' and ''S. pyogenes'' belong to the ''S. mitis'' and ''S. pyogenes'' groups, respectively,<ref>Liu, D., ''Molecular Detection of Human Bacterial Pathogens'' ([[Boca Raton, Florida|Boca Raton]]: [[CRC Press]], 2011), [https://books.google.com/books?id=nnGhc44bypAC&pg=PA324 p. 324].</ref> while the causative agent of [[dental caries]], ''[[Streptococcus mutans]]'', is basal to the ''Streptococcus'' group.
[[File:Streptococcus subclades.png|thumb|A conceptual diagram of ''Streptococcus'' subclade taxonomy based on phylogenetic trees and the [[conserved signature indels]] (CSIs) that are specifically shared by groups of streptococci.<ref name=":0"/> The number of CSIs identified for each group is shown.   ]]
Recent technological advances have resulted in an increase of available genome sequences for ''Streptococcus'' species, allowing for more robust and reliable phylogenetic and comparative genomic analyses to be conducted.<ref name=":0">{{cite journal | vauthors = Patel S, Gupta RS | title = Robust demarcation of fourteen different species groups within the genus Streptococcus based on genome-based phylogenies and molecular signatures | journal = Infection, Genetics and Evolution | volume = 66 | pages = 130–151 | date = December 2018 | pmid = 30248475 | doi = 10.1016/j.meegid.2018.09.020 | bibcode = 2018InfGE..66..130P | s2cid = 52813184 }}</ref> In 2018, the evolutionary relationships within ''Streptococcus'' was re-examined by Patel and Gupta through the analysis of comprehensive [[phylogenetic tree]]s constructed based on four different datasets of proteins and the identification of 134 highly specific molecular signatures (in the form of [[conserved signature indels]]) that are exclusively shared by the entire genus or its distinct subclades.<ref name=":0" />

The results revealed the presence of two main clades at the highest level within ''Streptococcus'', termed the "Mitis-Suis" and "Pyogenes-Equinus-Mutans" clades.<ref name=":0" /> The "Mitis-Suis" main clade comprises the Suis subclade and the Mitis clade, which encompasses the Angiosus, Pneumoniae, Gordonii and Parasanguinis subclades. The second main clade, the "Pyogenes-Equinus-Mutans", includes the Pyogenes, Mutans, Salivarius, Equinus, Sobrinus, Halotolerans, Porci, Entericus and Orisratti subclades. In total, 14 distinct subclades have been identified within the genus ''Streptococcus'', each supported by reliable branching patterns in phylogenetic trees and by the presence of multiple [[conserved signature indels]] in different proteins that are distinctive characteristics of the members of these 14 clades.<ref name=":0" /> A summary diagram showing the overall relationships among the ''Streptococcus'' based on these studies is depicted in a figure on this page.