Sinorhizobium meliloti phospholipase C required for lipid remodeling during phosphorus limitation

• Published in: Proceedings of the National Academy of Sciences - PNAS 2010-01, Vol.107 (1), p.302-307
• Main Authors: Zavaleta-Pastor, Maritza, Sohlenkamp, Christian, Gao, Jun-Lian, Guan, Ziqiang, Zaheer, Rahat, Finan, Turlough M, Raetz, Christian R.H, López-Lara, Isabel M, Geiger, Otto
• Format: Article
• Language: English
• Subjects: Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biological Sciences; Biosynthesis; cell membranes; Cells; diacylglycerols; Gene expression; Gene Expression Regulation, Bacterial; lipid metabolism; Lipids; Membrane lipids; Membrane Lipids - chemistry; Membrane Lipids - metabolism; Membranes; Molecular Structure; Mutation; nutrient availability; Phosphatases; Phosphates; Phosphatidylcholines; Phosphatidylcholines - metabolism; phosphatidylethanolamines; Phosphatidylethanolamines - metabolism; phospholipase C; Phospholipids; Phosphorus; Phosphorus - metabolism; Sinorhizobium meliloti; Sinorhizobium meliloti - cytology; Sinorhizobium meliloti - enzymology; Sinorhizobium meliloti - genetics; Triglycerides - chemistry; Triglycerides - metabolism; Type C Phospholipases - genetics; Type C Phospholipases - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0912930107

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.