Contact-induced molecular reorganization in E. coli model lipid membranes

TL;DR

This study investigates how physical contact with substrates influences the molecular organization and phase behavior of E. coli-like lipid membranes, revealing substrate-driven lipid domain formation and altered membrane dynamics.

Contribution

It demonstrates that membrane-surface interactions can spontaneously induce lipid domain formation in bacterial membranes, confirming theoretical predictions and highlighting their functional implications.

Findings

Substrate contact lowers membrane transition temperature by ~10°C.

It slows phase transition kinetics by nearly 100 times.

Local nanodomains with altered mechanical properties emerge over time.

Abstract

Biological membranes are complex, dynamic structures essential for cellular compartmentalization, signaling, and mechanical integrity. The molecular organization of eukaryotic membranes has been extensively studied, including the lipid raft-mediated lateral organization and the influence of the specific molecular interactions. Bacterial membranes were traditionally viewed as compositionally simpler and structurally uniform. Recent evidence, however, reveals that they possess significant lipid diversity and can form functional microdomains reminiscent of eukaryotic lipid rafts, despite lacking sterols and sphingolipids. Yet, the impact of unspecific physical contacts on the local molecular organization and evolution of the prokaryotic membranes remains poorly understood. Here we use a model lipid membrane mimicking the composition of Escherichia coli's inner membrane to investigate the impact of contacting substrates on the membrane nanoscale evolution, when close to its transition temperature, $T_m$. As expected, the presence of a substrate lowers the $T_m$ by $\sim$10 {\deg}C and induces a differential leaflet transition. However, it also slows down the phase transition kinetics by almost 2 orders of magnitude while simultaneously enabling a spinodal-like lateral molecular reorganization. This creates local alterations of the phase of the membrane, with the emergence of mechanically stiffer, yet still fluid nanodomains evolving over substrate-dependent timescales, consistent with a substrate-biased lipid flip-flop mechanism. The results verify previous theoretical predictions and demonstrate that a general physical mechanism -- driven by membrane-surface interactions -- can spontaneously induce lipid domain formation in bacterial membranes. This is bound to have notable consequences for its function and mechanical role, including in processes like osmotic pressure regulation.