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Published on: March 19, 2019
Quantifying adsorption and transport in Gram-positive cell walls by second-harmonic light scattering
Xiao-Hua Hu1, Yujie Li1, Franklin Mendelsohn1
1Department of Chemistry and Institute for Membranes and Interfaces, Temple University, 1901 N. 13th Street, Philadelphia, PA 19122, USA.
Biophysical Journal
|July 10, 2026
Summary
Researchers quantified antimicrobial transport in Gram-positive bacteria, finding outer layers allow rapid passage but the cytoplasmic membrane significantly slows entry. This reveals a consistent molecular uptake hierarchy across different bacterial cell envelopes.
Area of Science:
- Microbiology
- Biophysics
- Biochemistry
Background:
- Understanding bacterial cell wall interactions is crucial for environmental studies and drug development.
- Gram-positive bacteria have a distinct cell wall architecture compared to Gram-negative bacteria.
- Quantitative data on molecule transport in Gram-positive cell walls is lacking.
Purpose of the Study:
- To quantify adsorption and transport kinetics of malachite green in Gram-positive bacterial cell walls.
- To compare transport mechanisms between Gram-positive and Gram-negative bacteria.
- To elucidate the role of different cell wall layers in molecular uptake.
Main Methods:
- Time-resolved second harmonic light scattering was used.
- Kinetics were measured for malachite green transport across surface layer (SL), peptidoglycan mesh (PM), and cytoplasmic membrane (CM).
- Three Gram-positive species were studied: Lysinibacillus sphaericus, Bacillus subtilis, and Lacticaseibacillus rhamnosus.
Main Results:
- Transport through SL and PM was rapid.
- Translocation across the CM was two orders of magnitude slower, acting as a bottleneck.
- Despite architectural differences, Gram-positive and Gram-negative bacteria exhibit similar hierarchical molecular uptake regulation.
- Gram-positive SLs function similarly to Gram-negative porins for cation transport.
- Adsorption free energies were comparable between Gram-positive and Gram-negative bacteria.
Conclusions:
- The cytoplasmic membrane is the primary regulatory barrier for cytosolic entry in Gram-positive bacteria.
- Molecular uptake in bacteria is a hierarchical process, with outer layers providing accessibility and the lipid bilayer controlling entry rate.
- Surface layer (SL) of Gram-positive bacteria facilitates transport similarly to porins in Gram-negative bacteria.
