Editing Streptococcus (section)

==Natural genetic transformation==

[[Transformation (genetics)|Natural genetic transformation]] involves the transfer of DNA from one bacterium to another through the surrounding medium.  Transformation is a complex process dependent on the expression of numerous genes.  To be capable of transformation a bacterium must enter a special physiologic state referred to as [[Natural competence|competence]]. [[Streptococcus pneumoniae|''S. pneumoniae'']], [[Streptococcus mitis|''S. mitis'']] and [[Streptococcus oralis|''S. oralis'']] can become competent, and as a result actively acquire homologous DNA for transformation by a predatory fratricidal mechanism <ref name="pmid18485065">{{cite journal | vauthors = Johnsborg O, Eldholm V, Bjørnstad ML, Håvarstein LS | title = A predatory mechanism dramatically increases the efficiency of lateral gene transfer in Streptococcus pneumoniae and related commensal species | journal = Molecular Microbiology | volume = 69 | issue = 1 | pages = 245–253 | date = July 2008 | pmid = 18485065 | doi = 10.1111/j.1365-2958.2008.06288.x | s2cid = 30923996 | doi-access = free }}</ref>  This fratricidal mechanism mainly exploits non-competent siblings present in the same niche <ref name="pmid17277796">{{cite journal | vauthors = Claverys JP, Håvarstein LS | title = Cannibalism and fratricide: mechanisms and raisons d'être | journal = Nature Reviews. Microbiology | volume = 5 | issue = 3 | pages = 219–229 | date = March 2007 | pmid = 17277796 | doi = 10.1038/nrmicro1613 | s2cid = 35433490 }}</ref>   Among highly competent isolates of ''S. pneumoniae'', Li et al.<ref name="pmid27068094">{{cite journal | vauthors = Li G, Liang Z, Wang X, Yang Y, Shao Z, Li M, Ma Y, Qu F, Morrison DA, Zhang JR | display-authors = 6 | title = Addiction of Hypertransformable Pneumococcal Isolates to Natural Transformation for In Vivo Fitness and Virulence | journal = Infection and Immunity | volume = 84 | issue = 6 | pages = 1887–1901 | date = June 2016 | pmid = 27068094 | pmc = 4907133 | doi = 10.1128/IAI.00097-16 }}</ref> showed that nasal colonization fitness and virulence (lung infectivity) depend on an intact competence system.  Competence may allow the streptococcal pathogen to use external homologous DNA for recombinational repair of DNA damages caused by the host's oxidative attack.<ref name="pmid18295550">{{cite journal | vauthors = Michod RE, Bernstein H, Nedelcu AM | title = Adaptive value of sex in microbial pathogens | journal = Infection, Genetics and Evolution | volume = 8 | issue = 3 | pages = 267–285 | date = May 2008 | pmid = 18295550 | doi = 10.1016/j.meegid.2008.01.002 | bibcode = 2008InfGE...8..267M }}</ref>