Phospholipid synthesis in Borrelia burgdorferi: BB0249 and BB0721 encode functional phosphatidylcholine synthase and phosphatidylglycerolphosphate synthase proteins

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Abstract
Phospholipids are an important component of bacterial membranes.Borrelia burgdorferidiffers from many other bacteria in that it contains only two major membrane phospholipids: phosphatidylglycerol (PG) and phosphatidylcholine (PC).B. burgdorferiappears to lack enzymes required for synthesis of PC through the well-described methylation pathway. However,B. burgdorferidoes contain a gene (BB0249) with significant identity to a recently described phosphatidylcholine synthase gene (pcs) ofSinorhizobium meliloti. B. burgdorferialso contains a gene (BB0721) with significant identity to the gene (pgs) encoding phosphatidylglycerolphosphate synthase, an enzyme in the synthetic pathway of PG. Activity of BB0249 was confirmed by cloning the gene intoEscherichia coli, which does not produce PC. Transformation with a plasmid carryingBB0249resulted in production of PC byE. coli, but only in the presence of exogenously supplied choline, as would be predicted for a Pcs. Because loss of Pgs activity is lethal toE. coli, activity ofBB0721was confirmed by the ability of BB0721 to complement anE. coliPgs−mutant. A plasmid containingBB0721was transformed into a Pgs−mutant ofE. colicontaining a copy of the native gene on a temperature-regulated plasmid. The temperature-regulated plasmid was exchanged for a plasmid containingBB0721and it was shown that BB0721 was able to replace the lost Pgs function and restore bacterial growth. This study has established the existence and function of two critical enzymes in the synthesis of PC and PG inB. burgdorferi. Understanding of the biosynthetic pathways of PC and PG inB. burgdorferiis the first step in delineating the role of these phospholipids in the pathogenesis of Lyme disease.