How and Why Chaperone-Usher Pilus Rods Stretch

Engineering Escherichia coli MG1655 to Efficiently Produce 3-Deacyl-4'-monophosphoryl Lipid A

Monophosphoryl lipid A, derived from Salmonella minnesota R595, has been used in various adjuvant formulations. Escherichia coli can produce lipid A, but its structure is different. In this study, E. coli MG1655 has been engineered to efficiently produce the monophosphoryl lipid A. First, 126 genes relevant to the biosynthesis of the fimbriae, flagella, and ECA were deleted in MG1655, resulting in WQM027. Second, the genes pldA, mlaA, and mlaC related to the phospholipid transport system, the gene ptsG related to the carbohydrate phosphotransferase system, and the gene eptA encoding phosphoethanolamine transferase for lipid A modification were further deleted from WQM027, resulting in MW020. Third, lpxE from Francisella novicida and pagP and pagL from Salmonella were overexpressed in pFT24, resulting in pTEPL. pTEPL was transformed into MW020, resulting in MW020/pTEPL. Finally, fabI encoding an enoyl-ACP reductase was deleted from the genome of MW020/pTEPL, resulting in MW021/pTEPL. MW021/pTEPL could produce 85.31 mg/L of lipid A species after 26 h of fed-batch fermentation. Mainly two monophosphoryl lipid A species were produced in MW021/pTEPL, one is 3-deacyl-2-acyloxyacyl-4'-monophosphoryl lipid A and the other is 3-deacyl-4'-monophosphoryl lipid A. E. coli MW021/pTEPL constructed in this study could be an ideal host for the industrial production of monophosphoryl lipid A.

Construction of an Escherichia coli Strain Lacking Fimbriae by Deleting 64 Genes and Its Application for Efficient Production of Poly(3-Hydroxybutyrate) and l-Threonine

Escherichia coli contains 12 chaperone-usher operons for biosynthesis and assembly of various fimbriae. In this study, each of the 12 operons was deleted in E. coli MG1655, and the resulting 12 deletion mutants all grew better than the wild type, especially in the nutrient-deficient M9 medium. When the plasmid pBHR68 containing the key genes for polyhydroxyalkanoate production was introduced into these 12 mutants, each mutant synthesized more polyhydroxyalkanoate than the wild-type control. These results indicate that the fimbria removal in E. coli benefits cell growth and polyhydroxyalkanoate production. Therefore, all 12 chaperone-usher operons, including 64 genes, were deleted in MG1655, resulting in the fimbria-lacking strain WQM026. WQM026 grew better than MG1655, and no fimbria structures were observed on the surface of WQM026 cells. Transcriptomic analysis showed that in WQM026 cells, the genes related to glucose consumption, glycolysis, flagellar synthesis, and biosynthetic pathways of some key amino acids were upregulated, while the tricarboxylic acid cycle-related genes were downregulated. When pBHR68 was introduced into WQM026, huge amounts of poly-3-hydroxybutyrate were produced; when the plasmid pFW01-thrA*BC-rhtC, containing the key genes for l-threonine biosynthesis and transport, was transferred into WQM026, more l-threonine was synthesized than with the control. These results suggest that this fimbria-lacking E. coli WQM026 is a good host for efficient production of polyhydroxyalkanoate and l-threonine and has the potential to be developed into a valuable chassis microorganism. IMPORTANCE In this study, we investigated the interaction between the biosynthesis and assembly of fimbriae and intracellular metabolic networks in E. coli. We found that eliminating fimbriae could effectively improve the production of polyhydroxyalkanoate and l-threonine in E. coli MG1655. These results contribute to understanding the necessity of fimbriae and the advantages of fimbria removal for industrial microorganisms. The knowledge gathered from this study may be applied to the development of superior chassis microorganisms.