Engineering Escherichia coli for the production of saturated archaeal lipids

Archaeal membrane phospholipids have a different chemical composition than the phospholipids found in bacteria and eukaryotes. Typically, in archaea, phospholipids consist of saturated isoprenoid chains that are ether-bonded to glycerol 1-phosphate whereas in bacteria and eukaryotes, the main phospholipids are fatty acyl chains ester-bonded to glycerol 3-phosphate. This distinct chemical structure of phospholipids is believed to play a crucial role in enabling archaea to survive extreme environments and energy-limited conditions. Escherichia coli has previously been engineered to synthesize archaeal phospholipids next to its endogenous bacterial phospholipids. Cells equipped with these mixed heterochiral membranes were found to be viable with some improvement in robustness. However, a complete biosynthetic pathway for the production of substantial amounts of saturated archaeal lipids has not yet been realized in E. coli. Here, we engineered E. coli for the production of saturated archaeal phospholipids by introducing next to the geranylgeranyl reductase (GGR) and ferredoxin (Fd) from Methanosarcina acetivorans, the pyruvate-ferredoxin oxidoreductase (PFOR) from E. coli to allow for an efficient reduction of Fd. This resulted in a strain where approximately 75 % of the produced archaeal lipids are partially or completely saturated. Importantly, E. coli cells containing this mixed heterochiral membrane showed improved resistance to both heat and cold shock as compared to native E. coli strain. This E. coli strain with saturated archaeal phospholipids can serve as a valuable model for further engineering to incorporate different types of more complex archaeal membrane lipids.