Effects of producing high levels of hyperthermophile-specific C25,C25-archaeal membrane lipids in Escherichia coli

Abstract

A hyperthermophilic archaeon, Aeropyrum pernix, synthesizes C₂₅,C₂₅-archaeal membrane lipids, or extended archaeal membrane lipids, which contain two C₂₅ isoprenoid chains that are linked to glycerol-1-phosphate via ether bonds and are longer than the usual C₂₀,C₂₀-archaeal membrane lipids. The C₂₅,C₂₅-archaeal membrane lipids are believed to allow the archaeon to survive under harsh conditions, because they are able to form lipid membranes that are impermeable at temperatures approaching the boiling point. The effect that C₂₅,C₂₅-archaeal membrane lipids exert on living cells, however, remains unproven along with an explanation for why the hyperthermophilic archaeon synthesizes these specific lipids instead of the more common C₂₀,C₂₀-archaeal lipids or double-headed tetraether lipids. To shed light on the effects that these hyperthermophile-specific membrane lipids exert on living cells, we have constructed an E. coli strain that produces C₂₅,C₂₅-archaeal membrane lipids. However, a resultant low level of productivity would not allow us to assess the effects of their production in E. coli cells. Herein, we report an enhancement of the productivity of C₂₅,C₂₅-archaeal membrane lipids in engineered E. coli strains via the introduction of metabolic pathways such as an artificial isoprenol utilization pathway where the precursors of isoprenoids are synthesized via a two-step phosphorylation of prenol and isoprenol supplemented to a growth medium. In the strain with the highest titer, a major component of C₂₅,C₂₅-archaeal membrane lipids reached ∼11 % of total lipids of E. coli. It is noteworthy that the high production of the extended archaeal lipids did not significantly affect the growth of the bacterial cells. The permeability of the cell membrane of the strain became slightly lower in the presence of the exogenous membrane lipids with longer hydrocarbon chains, which demonstrated the possibility to enhance bacterial cell membranes by the hyperthermophile-specific lipids, along with the surprising robustness of the E. coli cell membrane.