Escherichia coli minicell membranes are enriched in cardiolipin

Abstract

The phospholipid composition of Escherichia coli minicells has been studied as a model for the cell division site. Minicells appeared to be enriched in cardiolipin at the expense of phosphatidylglycerol. Mass spectrometry showed no differences between the gross acyl chain compositions of minicells and wild-type cells.

FIG. 1

Minicell formation. (A) Schematic representation of normal cell division and minicell formation. (B) Microscopic images of the minicell-producing strain LMC1088. The upper panel shows a phase-contrast image, and the lower panel shows the corresponding DAPI fluorescence image. Note that the minicells lack DNA and therefore do not show DAPI fluorescence. Bar = 1 μm. (C) Phase-contrast image of isolated minicells.

FIG. 2

Comparison of phospholipid (PL) head group compositions of E. coli LMC500 (wild type), LMC1088 (mutant), and minicells. Values are averages from four, six, and six duplicate experiments with LMC500, LMC1088, and minicells, respectively.

FIG. 3

Positive-ion ESI-FTICR-MS analysis of E. coli phospholipids. A total phospholipid extract from wild-type cells was dissolved in dichloromethane-ethanol (7:3, vol/vol) and sprayed with 10 mM ammonium acetate. Expanded regions from broad-band mass spectra obtained after Fourier transformation of the ion cyclotron signal are shown. Individual phospholipid species are indicated by head group and overall acyl chain composition (expressed as x:y, where x is the number of carbon atoms and y is the number of unsaturated bonds). (A) Region between an m/z of 680 and an m/z of 800, containing mass spectral peaks derived from PE [M + H]⁺ (▪), PG [M + H]⁺ (▴), PG [M + NH₄]⁺ (▵), and PA [M + H]⁺ (♦). (B) Region between an m/z of 1,350 and an m/z of 1,500, containing mass spectral peaks derived from CL [M + H]⁺ (●).