A gene encoding phosphatidylethanolamine N-methyltransferase from Acetobacter aceti and some properties of its disruptant

N-methyltransferase (Pmt), which catalyzes methylation of phosphatidyle-thanolamine (PE) to PC, has been cloned and sequenced. One recombinant plasmid that complemented the PC biosynthesis was isolated from a gene library of the genomic DNA of A. aceti. The pmt gene encodes a polypeptide with molecular mass of either 25125, 26216, or 29052 for an about 27-kDa protein. The sequence of this gene showed significant similarity (44.3% identity in the similar sequence region) with the Rhodobacter sphaeroides pmtA gene which is involved in PE N-methylation. When the pmt gene was expressed in E.coli, which lacks PC, the Pmt activity and PC formation were clearly demonstrated. A. aceti strain harboring an interrupted pmt allele, pmt::Km, was constructed. The pmt disruption was confirmed by loss of Pmt and PC, and by Southern blot analyses. The null pmt mutant contained no PC, but tenfold more PE and twofold more phosphatidylglycerol (PG). The pmt disruptant did not show any dramatic effects on growth in basal medium supplemented with ethanol, but the disruption caused slow growth in basal medium supplemented with acetate. These results suggest that the lack of PC in the A. aceti membrane may be compensated by the increases of PE and PG by an unknown mechanism, and PC in A. acetic membrane is related to its acetic acid tolerance.