Abstract
Escherichia coli has been the leading model organism for many decades. It is a fundamental player in modern biology, facilitating the molecular biology revolution of the last century. The acceptance of E. coli as model organism is predicated primarily on the study of one E. coli lineage; E. coli K-12. However, the antecedents of today's laboratory strains have undergone extensive mutagenesis to create genetically tractable offspring but which resulted in loss of several genetic traits such as O antigen expression. Here we have repaired the wbbL locus, restoring the ability of E. coli K-12 strain MG1655 to express the O antigen. We demonstrate that O antigen production results in drastic alterations of many phenotypes and the density of the O antigen is critical for the observed phenotypes. Importantly, O antigen production enables laboratory strains of E. coli to enter the gut of the Caenorhabditis elegans worm and to kill C. elegans at rates similar to pathogenic bacterial species. We demonstrate C. elegans killing is a feature of other commensal E. coli. We show killing is associated with bacterial resistance to mechanical shear and persistence in the C. elegans gut. These results suggest C. elegans is not an effective model of human-pathogenic E. coli infectious disease.
Highlights
The outer membranes of Gram-negative bacteria function as a barrier to protect cells from toxic compounds such as antibiotics and detergents
To confirm that other strain-specific mutations are not responsible for the inability of E. coli MG1655 to produce O antigen, we complemented this mutation by cloning an intact version of wbbL into the pET20b vector
Decades of laboratory growth has resulted in off-spring with notable mutations and phenotypes that do not represent the true biology of the species
Summary
The outer membranes of Gram-negative bacteria function as a barrier to protect cells from toxic compounds such as antibiotics and detergents. Since its isolation in 1922, E. coli K-12 has become the workhorse of molecular biology During this time it has been repeatedly passaged and has been subjected to ionising radiation, ultraviolet light and mutagens, resulting in a number of genetic lesions and an organism which has lost the F plasmid, bacteriophage λ and the ability to produce many surface-associated structures (Hobman et al, 2007, Bachmann, 2004). In most E. coli K-12 strains this is due to the disruption of the wbbL gene by an IS5 element, termed the rfb-50 mutation By complementing this lesion with plasmid vectors, Reeves and colleagues demonstrated that wbbL encoded a rhamnose transferase and E. coli K-12 was capable of synthesising O16 serotype LPS (Stevenson et al., 1994, Liu & Reeves, 1994). We demonstrate that elaboration of the O antigen renders E. coli K-12 pathogenic in an accepted model of infection
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