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Investigating the Role of the Stringent Response in Lipid Modifications during the Stationary Phase in E. coli by Direct Analysis with Time-of-Flight-Secondary Ion Mass Spectrometry

Journal article
Authors Patrick M. Wehrli
Tina B. Angerer
Anne Farewell
John S. Fletcher
Johan Gottfries
Published in Analytical Chemistry
Volume 88
Issue 17
Pages 8680-8688
ISSN 0003-2700
Publication year 2016
Published at Department of Chemistry and Molecular Biology
Pages 8680-8688
Language en
Links pubs.acs.org/doi/full/10.1021/acs.a...
Subject categories Analytical Chemistry, Microbiology

Abstract

Escherichia coli is able to rapidly adjust the biophysical properties of its membrane phospholipids to adapt to environmental challenges including starvation stress. These membrane lipid modifications were investigated in glucose starved E. coli cultures and compared to a ΔrelAΔspoT (ppGpp0) mutant strain of E. coli, deficient in the stringent response, by means of time-of-flight-secondary ion mass spectrometry (TOF-SIMS). Recent advances in TOF-SIMS, through the implementation of gas cluster ion beams (GCIBs), now permit the analysis of higher mass species from native, underivatized, biological specimen, i.e., intact bacterial cells. Cultures in stationary phase were found to exhibit a radically different lipid composition as compared to cultures in the exponential growth phase. Wild-type E. coli reacted upon carbon starvation by lipid modifications including elongation, cyclopropanation, and increased cardiolipin formation. Observations are consistent with variants of cardiolipins (CL), phosphatidylglycerols (PG), phosphatidylethanolamines (PE), phosphatidic acids (PA), and fatty acids. Notably, despite having a proteomic profile and a gene expression profile somewhat similar to the wild-type during growth, the ppGpp0 mutant E. coli strain was found to exhibit modified phospholipids corresponding to unsaturated analogues of those found in the wild-type. We concluded that the ppGpp0 mutant reacts upon starvation stress by elongation and desaturation of fatty acyl chains, implying that only the last step of the lipid modification, the cyclopropanation, is under stringent control. These observations suggest alternative stress response mechanisms and illustrate the role of the RelA and SpoT enzymes in the biosynthetic pathway underlying these lipid modifications.

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