Insights into the structure of Escherichia coli outer membrane as the target for engineering microbial cell factories

Abstract

Escherichia coli is generally used as model bacteria to define microbial cell factories for many products and to investigate regulation mechanisms. E. coli exhibits phospholipids, lipopolysaccharides, colanic acid, flagella and type I fimbriae on the outer membrane which is a self-protective barrier and closely related to cellular morphology, growth, phenotypes and stress adaptation. However, these outer membrane associated molecules could also lead to potential contamination and insecurity for fermentation products and consume lots of nutrients and energy sources. Therefore, understanding critical insights of these membrane associated molecules is necessary for building better microbial producers. Here the biosynthesis, function, influences, and current membrane engineering applications of these outer membrane associated molecules were reviewed from the perspective of synthetic biology, and the potential and effective engineering strategies on the outer membrane to improve fermentation features for microbial cell factories were suggested.

Metabolic Engineering for Overproduction of Colanic Acid in Escherichia coli Mutant with Short Lipopolysaccharide

“…In bacteria, a small amount of CA could be synthesized constitutively. 2 However, in an extreme environment such as osmotic shock, 3 oxidative stress, 4 low pH, or low temperature, the synthesis of lipopolysaccharide in the outer membrane is affected, 5 meanwhile the production of CA significantly increases possibly to protect bacteria from these stresses. 3 In Escherichia coli MG1655, CA is formed by polymerizing D-glucose (Glc), D-galactose (Gal), L-fucose (Fuc), and Dglucuronic acid (GlcA) with a mole ratio of 1:2:2:1 and modifing with nonstoichiometric acetyl and pyruvate substituents 6,7 (Figure 1).…”

“…In E. coli MG1655, O-antigen repeat units could not be synthesized due to the IS5 insertion in wbbl, which is responsible for adding L-rhamnose to the O-antigen repeat unit. 5 MG1655wbbl + strain can synthesize the O16 antigen. 19,20 This indicates that enzymes required for Oantigen biosynthesis are still working in E. coli MG1655 to synthesize nucleotide sugars, which would consume carbon sources including glucose-1-phosphate and UDP-galactose.…”

“…19,20 This indicates that enzymes required for Oantigen biosynthesis are still working in E. coli MG1655 to synthesize nucleotide sugars, which would consume carbon sources including glucose-1-phosphate and UDP-galactose. 5 Besides, the ECA biosynthesis pathway also competes for Und-P with the CA biosynthesis pathway to carry out its assembly on the inner leaflet of the cytoplasmic membrane. 21 In this study, E. coli WQM001 was chosen to be the initial strain for further CA overproduction according to its high potential to produce CA.…”

“…In bacteria, a small amount of CA could be synthesized constitutively . However, in an extreme environment such as osmotic shock, oxidative stress, low pH, or low temperature, the synthesis of lipopolysaccharide in the outer membrane is affected, meanwhile the production of CA significantly increases possibly to protect bacteria from these stresses …”

“…MG1655 wbbl + strain can synthesize the O16 antigen. , This indicates that enzymes required for O-antigen biosynthesis are still working in E. coli MG1655 to synthesize nucleotide sugars, which would consume carbon sources including glucose-1-phosphate and UDP-galactose . Besides, the ECA biosynthesis pathway also competes for Und-P with the CA biosynthesis pathway to carry out its assembly on the inner leaflet of the cytoplasmic membrane …”