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. 2018 May 10;8(1):7470.
doi: 10.1038/s41598-018-25869-9.

Nutrient Depletion-Induced Production of Tri-Acylated Glycerophospholipids in Acinetobacter Radioresistens

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Free PMC article

Nutrient Depletion-Induced Production of Tri-Acylated Glycerophospholipids in Acinetobacter Radioresistens

Yu Luo et al. Sci Rep. .
Free PMC article

Abstract

Bacteria inhabit a vast range of biological niches and have evolved diverse mechanisms to cope with environmental stressors. The genus Acinetobacter comprises a complex group of Gram-negative bacteria. Some of these bacteria such as A. baumannii are nosocomial pathogens. They are often resistant to multiple antibiotics and are associated with epidemic outbreaks. A. radioresistens is generally considered to be a commensal bacterium on human skin or an opportunistic pathogen. Interestingly, this species has exceptional resistance to a range of environmental challenges which contributes to its persistence in clinical environment and on human skin. We studied changes in its lipid composition induced by the onset of stationary phase. This strain produced triglycerides (TG) as well as four common phospholipids: phosphatidylethanolamine (PE), phosphatidylglycerol (PG), cardiolipin (CL) and lysocardiolipin (LCL). It also produced small amounts of acyl-phosphatidylglycerol (APG). As the bacterial growth entered the stationary phase, the lipidome switched from one dominated by PE and PG to another dominated by CL and LCL. Surprisingly, bacteria in the stationary phase produced N-acyl-phosphatidylethanolamine (NAPE) and another rare lipid we tentatively name as 1-phosphatidyl-2-acyl-glycero-3-phosphoethanolamine (PAGPE) based on tandem mass spectrometry. It is possible these tri-acylated lipids play an important role in coping with nutrient depletion.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Thin-layer chromatogram and lipid composition of lipids extracted from A. radioresistens. TG (triglyceride), PG (phosphatidylglycerol), APG (acyl-phosphatidylglycerol), PAGPE (1-phosphatidyl-2-acyl-glycero-3-phosphoethanolamine, PE (phosphatidylethanolamine), CL (cardiolipin) and LCL (lysocardiolipin) were separated by TLC (thin-layer chromatography). (A) Thin-layer chromatogram developed in 75:25:4 chloroform/methanol/water. (B) Thin-layer chromatogram developed in 75:25:3:1 chloroform/methanol/water/acetic acid (glacial). The TLC sheets were stained with 0.02% primuline in 80:20 acetone/water. Representative fluorescent bands were analyzed by MS for identification. The lipid compositions are marked on the right. TG was likely diffused along the solvent front. (C) Semi-quantitative estimate of lipid composition based on primuline fluorescence.
Figure 2
Figure 2
Precursor scans for m/z 153 anionic head group fragment. The most abundant peaks of phosphatidylglycerol (PG) anions (m/z 747), CL double anions (m/z 700–701) and lysocardiolipin (LCL) double anions (m/z 582) are labeled. Top: Cells were grown for 11 h after inoculation. Middle: Cells were grown for 35 h. Bottom: Cells were grown for 7 d.
Figure 3
Figure 3
Precursor scans for m/z 140 anionic head group fragment. The most abundant peaks of phosphatidylethanolamine (PE), 1-phosphatidyl-2-acyl-glycero-3-phosphoethanolamine (PAGPE) and lyso-1-phosphatidyl-2-acyl-glycero-3-phosphoethanolamine (LPAGPE) anions are labeled. Top: Cells were grown for 11 h after inoculation. Middle: Cells were grown for 35 h. Bottom: Cells were grown for 7d.
Figure 4
Figure 4
Summary of chemical structures of tri-acylated glycerophospholipids. Chemical structures of acyl-phosphatidylglycerol (APG), N-acyl phosphatidylethanolamine (NAPE), lysocardiolipin (LCL), and 1-phosphatidyl-2-acyl-glycero-3-phosphoethanolamine (PAGPE) are shown. The predominant (16:0–18:1) phosphatidyl group shared by these lipids is shown in these structures. The third predominant fatty acyl group had a composition of either (16:0) or (18:1), as shown in this figure.
Figure 5
Figure 5
MS/MS spectrum of the m/z 1134 PAGPE anion and 2D-TLC chromatogram. (A) Dissociation and MS/MS spectrum of the m/z 1134 deprotonated anion. (B) The 2-D-TLC sheet was stained with 0.02% primuline. Representative fluorescent spots were analyzed by MS. The types of lipids recovered from silica gels are marked on the chromatogram. Positive MS spectrum of lipids recovered at the PAGPE spot is shown.
Figure 6
Figure 6
Dissociation and MS/MS spectrum of PAGPE cations. (A) Dissociation and MS/MS spectrum of the m/z 1136 protonated ion. (B) Dissociation and MS/MS spectrum of the m/z 1158 protonated ion. Two magnified areas of the spectrum are also shown.

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