Laboratory strains of Escherichia coli K-12: things are seldom what they seem

Abstract

Escherichia coli K-12 was originally isolated 100 years ago and since then it has become an invaluable model organism and a cornerstone of molecular biology research. However, despite its pedigree, since its initial isolation E. coli K-12 has been repeatedly cultured, passaged and mutagenized, resulting in an organism that carries many genetic changes. To understand more about this important model organism, we have sequenced the genomes of two ancestral K-12 strains, WG1 and EMG2, considered to be the progenitors of many key laboratory strains. Our analysis confirms that these strains still carry genetic elements such as bacteriophage lambda (λ) and the F plasmid, but also indicates that they have undergone extensive laboratory-based evolution. Thus, scrutinizing the genomes of ancestral E. coli K-12 strains leads us to examine whether E. coli K-12 is a sufficiently robust model organism for 21st century microbiology.

O antigen biogenesis sensitises Escherichia coli K-12 to bile salts, providing a plausible explanation for its evolutionary loss

“…51 in strain WG1 involves a large deletion between the dTDP-L-rhamnose synthesis gene rmlA and the colanic acid synthesis gene wcaF (Fig 1C) [18]. A plasmid carrying the intact wbbL from WG1 restored production of S-LPS in the EMG2 strain [14], confirming the independency of rfb mutational events in these two K-12 strains originating from the same institute.…”

“…The rfb-50 mutation in strain EMG2 is due to an IS5I insertion element in the coding sequence of WbbL, the second glycosyltransferase of RU O16 , abolishing the production of OAg O16 . Mutation rfb-51 in strain WG1 involves a large deletion between the dTDP-L-rhamnose synthesis gene rmlA and the colanic acid synthesis gene wcaF ( Fig 1C ) [ 18 ]. A plasmid carrying the intact wbbL from WG1 restored production of S-LPS in the EMG2 strain [ 14 ], confirming the independency of rfb mutational events in these two K-12 strains originating from the same institute.…”

Nonpathogenic E. coli engineered to surface display cytokines as a new platform for immunotherapy

“…DH5a here because for several reasons; it is a facultative anaerobe which facilitates tumor tropism, it is pansensitive to multiple commonly used antibiotics, it lacks Horizontal Gene Transfer (HGT) machinery, and its genetic modification has included knocking out its recombinant system, which makes this strain harder to obtain any mutations for possible resistance to antibiotics 22,23,[41][42][43][44] . Furthermore, it also lacks pks gene islands, present in E. coli Nissle 1917 and known to produce colibactin, a genotoxin associated with colorectal cancer 45 .…”

SOS-Inducing Drugs Trigger Nucleic Acid Release and Biofilm Formation in Gram-Negative Bacteria

“…Capsule-expressing strains, such as E. coli MG1655, which has the K-12 capsule, have commonly been used in SOS research. An additional factor may relate to the fact that highly passaged laboratory strains can become “domesticated”, with an SOS response that is blunted compared to wild-type strains [ 32 , 33 ]. A third factor is that the strength of the SOS response does vary from strain to strain.…”