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Inactivation of the gene for phospholipid N-methyltransferase in Sinorhizobium meliloti: phosphatidylcholine is

K E de Rudder1, I M López-Lara, O Geiger

  • 1Institute of Biotechnology, Technical University Berlin, Germany.

Molecular Microbiology
|September 6, 2000
PubMed

Insights

Sinorhizobium meliloti possesses two pathways for phosphatidylcholine (PC) biosynthesis. The methylation pathway, involving phospholipid N-methyltransferase (Pmt), is essential for normal growth, alongside the previously known PC synthase (Pcs) pathway.

Area of Science:

  • Microbiology
  • Biochemistry
  • Molecular Biology

Background:

  • Prokaryotes containing phosphatidylcholine (PC) were believed to utilize only the methylation pathway for its biosynthesis.
  • A second, choline-dependent pathway, PC synthase (Pcs), was identified in Sinorhizobium meliloti, condensing choline with CDP-diacylglyceride.

Purpose of the Study:

  • To characterize the methylation pathway of PC biosynthesis in S. meliloti.
  • To identify the gene responsible for the phospholipid N-methyltransferase (Pmt) activity.
  • To investigate the role of PC in S. meliloti growth.

Main Methods:

  • Complementation of a Pmt-deficient mutant with a S. meliloti gene bank.
  • DNA sequencing to identify the Pmt gene.
  • Growth analysis of wild-type, Pmt-deficient, and double Pmt/Pcs-deficient mutants under various conditions.

Main Results:

  • A novel S-adenosylmethionine-dependent N-methyltransferase gene (sinorhizobial Pmt) was identified, showing low similarity to its counterpart in Rhodobacter sphaeroides.
  • Expression of sinorhizobial Pmt produced PC and its methylated intermediates: monomethylphosphatidylethanolamine and dimethylphosphatidylethanolamine.
  • Pmt-deficient mutants exhibited significantly slower growth on minimal medium due to impaired PC formation, which was restored by choline availability via the Pcs pathway.
  • Double mutants lacking both Pmt and Pcs pathways were unable to synthesize PC and showed reduced growth even in the presence of choline.

Conclusions:

  • The methylation pathway, mediated by sinorhizobial Pmt, is crucial for PC biosynthesis and normal growth in S. meliloti.
  • PC is an essential component for optimal growth in S. meliloti.
  • S. meliloti utilizes both methylation and Pcs pathways for PC production, highlighting metabolic flexibility.

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