Sinorhizobium meliloti phospholipase C required for lipid remodeling during phosphorus limitation

• DOI: 10.1073/pnas.0912930107
• Publication Date: 2009-12-15T03:19:27Z
• Authors: Maritza Zavaleta-...; Christian Sohlenkamp; Jun-Lian Gao; Ziqiang Guan; Rahat Zaheer; Turlough M. Finan; Christian R. H. R...; Isabel M. López-Lara; Otto Geiger
• Keywords: 2. Zero hunger; 0303 health sciences; Molecular Structure; Phosphatidylethanolamines; Phosphorus; Gene Expression Regulation, Bacterial; 6. Clean water; Membrane Lipids; 03 medical and health sciences; Bacterial Proteins; Type C Phospholipases; Mutation; Phosphatidylcholines; Triglycerides; Sinorhizobium meliloti

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.