Principles of membrane adaptation revealed through environmentally induced bacterial lipidome remodeling

Chwastek, G.; Surma, M. A.; Rizk, S.; Grosser, D.; Lavrynenko, O.; Rucińska, M.; Jambor, H.; Sáenz, J. (2020) Cell Reports, 32(12), 108165. DOI: 10.1016/j.celrep.2020.108165

Summary

All cells adapt their membrane lipid composition in response to environmental changes, yet the global patterns of this remodeling are poorly understood. Using shotgun lipidomics, we characterized the lipidome of [[methylobacterium-extorquens|Methylobacterium extorquens]] across varying temperatures (6–30 °C), osmotic stress, detergent challenge, carbon sources, and growth phases. We found that only 11 of 27 total lipid species account for 90% of lipidomic variability, constraining the upper limit of lipids required for an adaptive living membrane. Critically, acyl chain remodeling is not evenly distributed across lipid headgroup classes, implicating headgroup-specific acyl chain remodeling as a mechanism for fine-tuning membrane physical properties.

Key Findings

• M. extorquens has a simple lipidome of ~27 species across 5 classes: phosphatidylglycerol (PG), phosphatidylethanolamine (PE), phosphatidylcholine (PC), cardiolipin (CL), and Diplopterol (including 2-methyl-diplopterol).
• Only 11 lipid species account for 90% of total lipidomic variability across all environmental perturbations — less than half the total available species.
• Temperature had by far the largest effect on lipidome remodeling, with >2-fold more variability than any other condition. Growth on different carbon sources and detergent challenge had minimal effects.
• Acyl chain remodeling (saturation, chain length) is unevenly distributed across headgroup classes. PE showed the greatest acyl chain variability, while PG was relatively stable. This means the same change in acyl chain composition has headgroup-dependent effects on membrane properties.
• The major phospholipid acyl chains are 16:1 and 18:1, with double bonds at the ω7 and ω13 positions — notably, the ω7 position corresponds to Δ11, which later proved critical for hopanoid-phospholipid interactions (Nguyen et al., 2024, Biophysical Journal).
• Di-unsaturated C18:2 fatty acids were confirmed by MS/MS, rare in Methylobacterium and potentially significant for cold adaptation.

Methods

• Shotgun lipidomics: high-resolution mass spectrometry (Lipotype GmbH) for absolute quantification of 25 phospholipid species and 2 hopanoid species.
• Environmental perturbations: temperatures (6–30 °C), NaCl (0–0.2 M), Triton X-100, methanol (0.1–1%), growth phases (early exponential to stationary).
• Principal component analysis: to identify global patterns in lipidomic variability.
• Fatty acid methyl ester (FAME) analysis: GC-MS to confirm double bond positions (ω7 and ω13).

Significance

This paper established M. extorquens as a quantitative model system for studying membrane adaptation and laid the foundation for understanding lipidome design principles. The finding that headgroup-specific acyl chain remodeling tunes membrane properties suggested a previously unrecognized mechanism for homeostatic control. This work directly informed later studies on minimal cell lipidomes and the discovery that double bond position modulates hopanoid ordering.