Editing Mycobacterium smegmatis (section)

== Genetics and genomics ==
The genomes of multiple strains of ''M. smegmatis'' have been sequenced by [[J. Craig Venter Institute|TIGR]] and other laboratories, including the "wild-type" (mc<sup>2</sup> 155) and some antibiotic-resistant strains (4XR1/R2).<ref>{{cite journal | vauthors = Mohan A, Padiadpu J, Baloni P, Chandra N | title = Complete Genome Sequences of a Mycobacterium smegmatis Laboratory Strain (MC2 155) and Isoniazid-Resistant (4XR1/R2) Mutant Strains | journal = Genome Announcements | volume = 3 | issue = 1 | date = February 2015 | pmid = 25657281 | pmc = 4319614 | doi = 10.1128/genomeA.01520-14 }}</ref> The genome of strain mc<sup>2</sup>155 is ~6,9 Mbp long and encodes ~6400 proteins<ref>{{Cite web|title=Mycolicibacterium smegmatis (ID 1026) - Genome - NCBI|url=https://www.ncbi.nlm.nih.gov/genome/?term=txid1772%5BOrganism:exp%5D|access-date=2021-06-16|website=www.ncbi.nlm.nih.gov}}</ref> which is relatively large for bacteria (for comparison, the genome of [[Escherichia coli|E. coli]] encodes about 4000 proteins).

This species shares more than 2000 homologous genes with ''M. tuberculosis'' and thus is a good model organism to study mycobacteria in general and the highly pathogenic ''M. tuberculosis'' in particular; however, only 12 of the 19 virulence genes in ''M. tuberculosis'' have homologues in ''M. smegmatis''.<ref>{{cite journal |last1=Reyrat |first1=Jean-Marc |last2=Kahn |first2=Daniel |title=Mycobacterium smegmatis: an absurd model for tuberculosis? |journal=Trends in Microbiology |date=October 2001 |volume=9 |issue=10 |pages=472–473 |doi=10.1016/S0966-842X(01)02168-0}}</ref><ref>{{cite journal |last1=Camacho |first1=Luis Reinaldo |last2=Ensergueix |first2=Danielle |last3=Perez |first3=Esther |last4=Gicquel |first4=Brigitte |last5=Guilhot |first5=Christophe |title=Identification of a virulence gene cluster of Mycobacterium tuberculosis by signature-tagged transposon mutagenesis |journal=Molecular Microbiology |date=October 1999 |volume=34 |issue=2 |pages=257–267 |doi=10.1046/j.1365-2958.1999.01593.x|doi-access=free }}</ref><ref>{{cite journal |last1=Glickman |first1=Michael S |last2=Cox |first2=Jeffery S |last3=Jacobs |first3=William R |title=A Novel Mycolic Acid Cyclopropane Synthetase Is Required for Cording, Persistence, and Virulence of Mycobacterium tuberculosis |journal=Molecular Cell |date=April 2000 |volume=5 |issue=4 |pages=717–727 |doi=10.1016/s1097-2765(00)80250-6|doi-access=free }}</ref><ref>{{cite journal |last1=Berthet |first1=François-Xavier |last2=Lagranderie |first2=Micheline |last3=Gounon |first3=Pierre |last4=Laurent-Winter |first4=Christine |last5=Ensergueix |first5=Danielle |last6=Chavarot |first6=Pierre |last7=Thouron |first7=Françoise |last8=Maranghi |first8=Eddie |last9=Pelicic |first9=Vladimir |last10=Portnoı̈ |first10=Denis |last11=Marchal |first11=Gilles |last12=Gicquel |first12=Brigitte |title=Attenuation of Virulence by Disruption of the Mycobacterium tuberculosis erp Gene |journal=Science |date=23 October 1998 |volume=282 |issue=5389 |pages=759–762 |doi=10.1126/science.282.5389.759}}</ref>

The discovery of [[plasmid]]s, [[bacteriophage|phages]], and [[mobile genetic elements]] has enabled the construction of dedicated gene-inactivation and gene reporter systems. The ''M. smegmatis'' mc<sup>2</sup>155 strain is hypertransformable, and is now the work-horse of mycobacterial genetics.{{cn|date=April 2023}}

===Transformation===
Transformation is a process by which a bacterial cell takes up DNA that had been released by another cell into the surrounding medium, and then incorporates that DNA into its own genome by homologous recombination (see [[Transformation (genetics)]]).  Strains of ''M. smegmatis'' that have particularly efficient DNA repair machinery, as indicated by their greater resistance to the DNA damaging effects of agents such as UV and mitomycin C, proved to be the most capable of undergoing transformation.<ref name="pmid641008">{{cite journal | vauthors = Norgard MV, Imaeda T | title = Physiological factors involved in the transformation of Mycobacterium smegmatis | journal = Journal of Bacteriology | volume = 133 | issue = 3 | pages = 1254–62 | date = March 1978 | pmid = 641008 | pmc = 222159 | doi = 10.1128/jb.133.3.1254-1262.1978 }}</ref>  This suggests that transformation in ''M. smegmatis'' is a DNA repair process, presumably a recombinational repair process, as it is in other bacterial species.<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 = 267–85 | date = May 2008 | pmid = 18295550 | doi = 10.1016/j.meegid.2008.01.002 }}</ref>

===Conjugation===
Conjugal DNA transfer in ''M. smegmatis'' requires stable and extended contact between a donor and a recipient strain, is DNase resistant, and the transferred DNA is incorporated into the recipient’s chromosome by homologous recombination.  However, in contrast to the well-known ''E. coli'' Hfr conjugation system, in ''M. smegmatis'' all regions of the chromosome are transferred with comparable efficiencies and mycobacterial conjugation is chromosome, rather than plasmid based.  Gray et al.<ref name="pmid23874149">{{cite journal | vauthors = Gray TA, Krywy JA, Harold J, Palumbo MJ, Derbyshire KM | title = Distributive conjugal transfer in mycobacteria generates progeny with meiotic-like genome-wide mosaicism, allowing mapping of a mating identity locus | journal = PLOS Biology | volume = 11 | issue = 7 | pages = e1001602 | date = July 2013 | pmid = 23874149 | pmc = 3706393 | doi = 10.1371/journal.pbio.1001602 | doi-access = free }}</ref> reported substantial blending of the parental genomes resulting from conjugation and referred to this blending as reminiscent of that seen in the meiotic products of sexual reproduction (see [[Evolution of sexual reproduction#Origin of sexual reproduction|Origin of sexual reproduction]]).{{cn|date=April 2023}}