Understanding the role of membrane lipids in mechanism of antimicrobial photodynamic therapy in Escherichia coli

Abstract Antimicrobial photodynamic therapy (aPDT) is a promising alternative to antibiotics, yet the molecular factors determining bacterial susceptibility remain unclear. This study investigates the critical role of bacterial lipids, particularly cardiolipin (CL) in the aPDT response of Escherichia coli using methylene blue as a photosensitizer. Through genetic deletion (ΔclsABC) and chemical modification via mannitol supplementation, we demonstrate that reduced CL levels significantly enhance bacterial sensitivity, leading to an additional reduction in viability exceeding 3 log10. Quantitative lipidomics (MS,GC) confirmed substantial CL depletion and altered fatty acid saturation. Interestingly, while live CL-deficient cells were more vulnerable, biomimetic giant unilamellar vesicles (GUVs) with higher CL content showed greater susceptibility to photo-oxidation. These findings suggest that CL-rich microdomains in living bacteria act as functional scaffolds for stress-defense systems rather than mere targets for oxidative damage. Modulating membrane lipid composition thus represents a novel strategy to potentiate aPDT efficacy.