Document Detail

Rhizobium meliloti mutants deficient in phospholipid N-methyltransferase still contain phosphatidylcholine.
MedLine Citation:
PMID:  9371435     Owner:  NLM     Status:  MEDLINE    
Phosphatidylcholine (PC) is the major membrane-forming phospholipid in eukaryotes. In addition to this structural function, PC is thought to play a major role in lipid turnover and signalling in eukaryotic systems. In prokaryotes, only some groups of bacteria, among them the members of the family Rhizobiaceae, contain PC. To understand the role of PC in bacteria, we have studied Rhizobium meliloti 1021, which is able to form nitrogen-fixing nodules on its legume host plants and therefore has a very complex phenotype. R. meliloti was mutagenized with N-methyl-N'-nitro-N-nitrosoguanidine, and potential mutants defective in phospholipid N-methyltransferase were screened by using a colony autoradiography procedure. Filters carrying lysed replicas of mutagenized colonies were incubated with S-adenosyl-L-[methyl-14C]methionine. Enzymatic transfer of methyl groups to phosphatidylethanolamine (PE) leads to the formation of PC and therefore to the incorporation of radiolabel into lipid material. Screening of 24,000 colonies for reduced incorporation of radiolabel into lipids led to the identification of seven mutants which have a much-reduced specific activity of phospholipid N-methyltransferase. In vivo labelling of mutant lipids with [14C]acetate showed that the methylated PC biosynthesis intermediates phosphatidylmonomethylethanolamine and phosphatidyldimethylethanolamine are no longer detectable. This loss is combined with a corresponding increase in the potential methyl acceptor PE. These results indicate that PC biosynthesis via the methylation pathway is indeed blocked in the mutants isolated. However, mass spectrometric analysis of the lipids shows that PC was still present when the mutants had been grown on complex medium and that it was present in the mutants in wild-type amounts. In vivo labelling with [methyl-14C]methionine shows that in phospholipid N-methyltransferase-deficient mutants, the choline moiety of PC is not formed by methylation. These findings suggest the existence of a second pathway for PC biosynthesis in Rhizobium.
K E de Rudder; J E Thomas-Oates; O Geiger
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of bacteriology     Volume:  179     ISSN:  0021-9193     ISO Abbreviation:  J. Bacteriol.     Publication Date:  1997 Nov 
Date Detail:
Created Date:  1997-12-12     Completed Date:  1997-12-12     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  2985120R     Medline TA:  J Bacteriol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  6921-8     Citation Subset:  IM    
Institute of Biotechnology, Technical University of Berlin, Germany.
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MeSH Terms
Acetates / metabolism
Chromatography, Thin Layer
Culture Media / metabolism
Lipid Metabolism
Lipids / analysis
Mass Spectrometry
Methyltransferases / genetics*,  metabolism*
Phosphatidylcholines / metabolism*
Phosphatidylethanolamine N-Methyltransferase
Phosphatidylethanolamines / metabolism
S-Adenosylmethionine / metabolism
Sinorhizobium meliloti / genetics*,  growth & development,  metabolism*
Reg. No./Substance:
0/Acetates; 0/Culture Media; 0/Lipids; 0/Phosphatidylcholines; 0/Phosphatidylethanolamines; 29908-03-0/S-Adenosylmethionine; 70-25-7/Methylnitronitrosoguanidine; EC 2.1.1.-/Methyltransferases; EC N-Methyltransferase

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