Sinorhizobium meliloti phospholipase C required for lipid remodeling during phosphorus limitation.
Rhizobia are Gram-negative soil bacteria able to establish nitrogen-fixing root nodules with their respective legume host plants. Besides phosphatidylglycerol, cardiolipin, and phosphatidylethanolamine, rhizobial membranes contain phosphatidylcholine (PC) as a major membrane lipid. Under phosphate-limiting conditions of growth, some bacteria replace their membrane phospholipids with lipids lacking phosphorus. In Sinorhizobium meliloti, these phosphorus-free lipids are sulfoquinovosyl diacylglycerol, ornithine-containing lipid, and diacylglyceryl trimethylhomoserine (DGTS). Pulse-chase experiments suggest that the zwitterionic phospholipids phosphatidylethanolamine and PC act as biosynthetic precursors of DGTS under phosphorus-limiting conditions. A S. meliloti mutant, deficient in the predicted phosphatase SMc00171 was unable to degrade PC or to form DGTS in a similar way as the wild type. Cell-free extracts of Escherichia coli, in which SMc00171 had been expressed, convert PC to phosphocholine and diacylglycerol, showing that SMc00171 functions as a phospholipase C. Diacylglycerol , in turn, is the lipid anchor from which biosynthesis is initiated during the formation of the phosphorus-free membrane lipid DGTS. Inorganic phosphate can be liberated from phosphocholine. These data suggest that, in S. meliloti under phosphate-limiting conditions, membrane phospholipids provide a pool for metabolizable inorganic phosphate, which can be used for the synthesis of other essential phosphorus-containing biomolecules. This is an example of an intracellular phospholipase C in a bacterial system; however, the ability to degrade endogenous preexisting membrane phospholipids as a source of phosphorus may be a general property of Gram-negative soil bacteria.
Zavaleta-Pastor
Maritza
M
Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62251, Mexico.
Sohlenkamp
Christian
C
Gao
Jun-Lian
JL
Guan
Ziqiang
Z
Zaheer
Rahat
R
Finan
Turlough M
TM
Raetz
Christian R H
CR
López-Lara
Isabel M
IM
Geiger
Otto
O
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D009154:Mutation; D010713:Phosphatidylcholines / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism*; D016962:Sinorhizobium meliloti / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D014280:Triglycerides / Q000737:chemistry / Q000378:metabolism; D010738:Type C Phospholipases / Q000235:genetics / Q000378:metabolism*
C021660:1(3),2-diacylglyceryl-3(1)-O-4'-(N,N,N-trimethyl)homoserine; D001426:Bacterial Proteins; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D014280:Triglycerides; D010758:Phosphorus; C483858:phosphatidylethanolamine; D010738:Type C Phospholipases