Sinorhizobium meliloti phospholipase C required for lipid remodeling during phosphorus limitation

Abstract

Rhizobia are Gram-negative soil bacteria able to establish nitrogenfixing 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, ornithinecontaining 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.nimal cells have access to relatively abundant sources of phosphorus for the formation of biomolecules such as membrane phospholipids and nucleic acids. The characteristic lipid composition for a particular animal cell membrane is thought to result from a steady state between formation and turnover of the lipids. In contrast, plants and many environmental microbes often live in environments where available phosphorus is a growth-limiting factor. The strategies employed by organisms to deal with phosphorus limitation include: (i) increased solubilization of phosphorus-containing compounds; (ii) more efficient uptake into cells; and (iii) less phosphorus use when synthesizing their biomolecules (1). The replacement of phospholipids by galacto-and sulfolipids in plant membranes constitutes an important adaptive process for growth on phosphate-limited soils. In Arabidopsis thaliana, several phospholipases D and C (2-5) are induced under phosphate-limiting conditions, and they degrade membrane phospholipids to phosphatidic acid or diacylglycerol (DAG), respectively. DAG then serves as the initial substrate for the formation of galacto-and sulfolipids, which lack phosphorus.In some bacteria, the membrane phospholipids are partially replaced during phosphate limitation by phosphoru...

Comparative genomic, proteomic and exoproteomic analyses of three Pseudomonas strains reveals novel insights into the phosphorus scavenging capabilities of soil bacteria

“…A total of 267 proteins were significantly enriched [ t ‐test, P value ≤ 0.05, fold‐change (log2) ≥ 1.5] during Pi depletion and there was concordance between the two datasets. These enriched proteins included the transmembrane and ATP‐binding domains of the Pst system (PstC, PstA, PstB), a 2‐aminoethylphosphonate (2‐AEP)–specific phosphonatase (PhnX, PhnW) (Jiang et al ., 1995; Baker et al ., 1998; White and Metcalf, 2007), proteins involved in lipid remodelling (PlcP, DagK, OlsA, OlsB, Cfa, TauD) (Liu and Hulett, 1998; Antelmann et al ., 2000; Zavaleta‐Pastor et al ., 2010; Carini et al ., 2015; Sebastian et al ., 2016), a putative intracellular phosphatase (UxpA) and the twin‐arginine translocation (TAT) pathway (Putker et al ., 2013) (Table 2). Proteins for both starch (MalQ, GlgE, GlgX, GlpA and GlpB) and polyhydroxyalkanoic acid (PhaA, PhaG, PhaC) biosynthesis (carbon storage) were also enriched during Pi stress (Supporting Information Table S4).…”

“…We found genes encoding for the key proteins required for lipid remodelling (PlcP, DagK, OlsA and OlsB) in the genomes of all Pseudomonas strains scrutinised (Gao et al ., 2004; Zavaleta‐Pastor et al ., 2010). Furthermore, in BIRD‐1 these proteins were expressed in a PHO‐dependent manner.…”

Homeostasis and Catabolism of Choline and Glycine Betaine: Lessons from Pseudomonas aeruginosa

“…This liberation could be a consequence of the presence of one or more bacterial phospholipase Cs (PLCs), but how this process is regulated is not known. Such a utilization of lipid headgroups is plausible; bacteria under conditions of phosphate starvation can selectively hydrolyze phospholipids to support the intracellular phosphate requirements (75). The potential role for bPC as a choline store has not been tested in P. aeruginosa, but lack of strong phenotypes for the P. aeruginosa ⌬pcs mutant under a variety of conditions does suggest that the role of bPC, if any, manifests only in situations not yet tested (73).…”

Phosphorus supply drives rapid turnover of membrane phospholipids in the diatom Thalassiosira pseudonana

“…For example, all phytoplankton groups examined to date, both in culture and in situ, substitute non-phosphorus (sulfur-and nitrogen-containing) lipids for phospholipids in their membranes under low-P conditions (Van Mooy et al, 2009). Such lipid substitution in bacteria (Minnikin et al, 1974;Benning et al, 1995) can take place within hours (Zavaleta-Pastor et al, 2010). However, it is not known how rapidly phytoplankton remodel their membranes, and whether field observations (Van Mooy et al, 2009) reflect longterm adjustment to the environment or an immediate cellular response to low-P conditions.…”