Editing Escherichia coli (section)

===Cell cycle===
{{main|Cell cycle}}

The bacterial cell cycle is divided into three stages.  The B period occurs between the completion of cell division and the beginning of [[DNA replication]].  The C period encompasses the time it takes to replicate the [[Cytogenetics|chromosomal DNA.]]  The D period refers to the stage between the conclusion of [[DNA replication]] and the end of cell division.<ref name="Wang2009">{{cite journal | vauthors = Wang JD, Levin PA | title = Metabolism, cell growth and the bacterial cell cycle | journal = Nature Reviews. Microbiology | volume = 7 | issue = 11 | pages = 822–27 | date = November 2009 | pmid = 19806155 | pmc = 2887316 | doi = 10.1038/nrmicro2202 }}</ref>  The doubling rate of ''E. coli'' is higher when more nutrients are available.  However, the length of the C and D periods do not change, even when the doubling time becomes less than the sum of the C and D periods.  At the fastest growth rates, replication begins before the previous round of replication has completed, resulting in multiple replication forks along the [[DNA]] and overlapping cell cycles.<ref name="Cooper1968">{{cite journal | vauthors = Cooper S, Helmstetter CE | title = Chromosome replication and the division cycle of ''Escherichia coli'' B/r | journal = Journal of Molecular Biology | volume = 31 | issue = 3 | pages = 519–40 | date = February 1968 | pmid = 4866337 | doi = 10.1016/0022-2836(68)90425-7 }}</ref>

The number of replication forks in fast growing ''E. coli'' typically follows 2n (n = 1, 2 or 3). This only happens if [[DNA replication|replication]] is initiated simultaneously from all [[Origin of replication|origins of replications]], and is referred to as synchronous [[DNA replication|replication]]. However, not all cells in a culture replicate synchronously. In this case cells do not have multiples of two [[replication fork]]s. Replication initiation is then referred to being asynchronous.<ref name=":2">{{cite journal | vauthors = Skarstad K, Boye E, Steen HB | title = Timing of initiation of chromosome replication in individual Escherichia coli cells | journal = The EMBO Journal | volume = 5 | issue = 7 | pages = 1711–7 | date = July 1986 | pmid = 3527695 | pmc = 1166998 | doi = 10.1002/j.1460-2075.1986.tb04415.x }}</ref> However, asynchrony can be caused by mutations to for instance [[DnaA]]<ref name=":2" /> or [[DnaA]] initiator-associating protein [[DiaA]].<ref>{{cite journal | vauthors = Ishida T, Akimitsu N, Kashioka T, Hatano M, Kubota T, Ogata Y, Sekimizu K, Katayama T | display-authors = 6 | title = DiaA, a novel DnaA-binding protein, ensures the timely initiation of ''Escherichia coli'' chromosome replication | journal = The Journal of Biological Chemistry | volume = 279 | issue = 44 | pages = 45546–55 | date = October 2004 | pmid = 15326179 | doi = 10.1074/jbc.M402762200 | doi-access = free }}</ref>

Although ''E. coli'' reproduces by [[fission (biology)|binary fission]] the two supposedly identical cells produced by cell division are functionally asymmetric with the old pole cell acting as an aging parent that repeatedly produces rejuvenated offspring.<ref name="Stewart_2005">{{cite journal | vauthors = Stewart EJ, Madden R, Paul G, Taddei F | title = Aging and death in an organism that reproduces by morphologically symmetric division | journal = PLOS Biology | volume = 3 | issue = 2 | pages = e45 | date = February 2005 | pmid = 15685293 | pmc = 546039 | doi = 10.1371/journal.pbio.0030045 | doi-access = free }}</ref> When exposed to an elevated stress level, damage accumulation in an old ''E. coli'' lineage may surpass its immortality threshold so that it arrests division and becomes mortal.<ref name="Proenca_2019">{{cite journal | vauthors = Proenca AM, Rang CU, Qiu A, Shi C, Chao L | title = Cell aging preserves cellular immortality in the presence of lethal levels of damage | journal = PLOS Biology | volume = 17 | issue = 5 | pages = e3000266 | date = May 2019 | pmid = 31120870 | pmc = 6532838 | doi = 10.1371/journal.pbio.3000266 | doi-access = free }}</ref> [[cellular senescence|Cellular aging]] is a general process, affecting [[prokaryote]]s and [[eukaryote]]s alike.<ref name="Proenca_2019" />