Inactivation of the gene for phospholipid N‐methyltransferase in Sinorhizobium meliloti: phosphatidylcholine is required for normal growth

Abstract

In phosphatidylcholine (PC)‐containing prokaryotes, only the methylation pathway of PC biosynthesis was thought to occur. However, a second choline‐dependent pathway for PC formation, the PC synthase (Pcs) pathway, exists in Sinorhizobium (Rhizobium) meliloti in which choline is condensed with CDP‐diacylglyceride. Here, we characterize the methylation pathway of PC biosynthesis in S. meliloti. A mutant deficient in phospholipid N‐methyltransferase (Pmt) was complemented with a S. meliloti gene bank and the complementing DNA was sequenced. A gene coding for a S‐adenosylmethionine‐dependent N‐methyltransferase was identified as the sinorhizobial Pmt, which showed little similarity to the corresponding enzyme from Rhodobacter sphaeroides. Upon expression of the sinorhizobial Pmt, besides phosphatidylcholine, the methylated intermediates of the methylation pathway, monomethylphosphatidylethanolamine and dimethylphosphatidylethanolamine, are also formed. When Pmt‐deficient mutants of S. meliloti are grown on minimal medium, they cannot form PC, and they grow significantly more slowly than the wild type. Growth of the Pmt‐deficient mutant in the presence of choline allows for PC formation via the Pcs pathway and restores wild‐type‐like growth. Double knock‐out mutants, deficient in Pmt and in Pcs, are unable to form PC and show reduced growth even in the presence of choline. These results suggest that PC is required for normal growth of S. meliloti.

OlsG (Sinac_1600) Is an Ornithine Lipid N-Methyltransferase from the Planctomycete Singulisphaera acidiphila

“…2). Two families of bacterial phospholipid N-methyltransferases (Pmts) have been described (21,28,29). A third bacterial lipid N-methyltransferase is BtaB, involved in the synthesis of the betaine lipid diacylglyceryl-N,N,N-trimethylhomoserine (DGTS) (30,31).…”

“…The N-Methyltransferase OlsG Uses OL as Substrate-OlsG is a homolog of the phospholipid N-methyltransferase PmtA from S. meliloti (SmPmtA) (21). It is composed of 192 amino acid residues and shares 29% identity on amino acid level with SmPmtA.…”

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

“…Geiger and his colleagues have recently described a novel pathway by which some bacteria may generate PC (de Rudder et al, 2000;Lopez-Lara & Geiger, 2001;Sohlenkamp et al, 2000Sohlenkamp et al, , 2003. In this pathway, which was first described for Sinorhizobium meliloti, a phosphatidylcholine synthase (Pcs) directly condenses exogenously acquired choline with CDP-DAG to form PC.…”

In Vitro Characterization of the Enzyme Properties of the Phospholipid N -Methyltransferase PmtA from Agrobacterium tumefaciens

“…Two families can be distinguished, the Rhodobacter PmtA family (1) and the Sinorhizobium PmtA family (10). Members of the two families are only distantly related and are often more similar to methyltransferases with other substrate specificities than to each other (26,37).…”