Pawlik, K. J. | bioRxiv Science

bioRxiv2026

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

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 ({Delta}clsABC) 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.

microbiology↗

bioRxiv2024

The gamma-butyrolactone receptors ScbR and AtrA form a quorum sensing switch between coelimycin and actinorhodin synthesis in Streptomyces coelicolor A3(2)

BackgroundQuorum sensing enables gene expression regulation in response to changes in cell population density and controls diverse processes, such as biofilm formation, virulence and antibiotic production, in bacteria. In one of the largest, soil-dominant phylum Actinobacteria, cell-to-cell communication occurs through the small, membrane-diffusible signalling molecules gamma-butyrolactones (GBLs). Their actions are exerted through receptor proteins that also act as response regulators in a one-component system manner. With only a few GBL systems characterized, most of them come from the large, antibiotic-producer genus Streptomyces. In the model organism Streptomyces coelicolor A3(2), two GBL receptors, ScbR and SlbR, which are both antibiotic production repressors, have been reported so far. ResultsIn this work, we identified a new GBL receptor protein, the conserved and pleiotropic regulator AtrA, which has an activating mode of action. Moreover, we elucidated the precise mechanism by which it controls the production of the antibiotic actinorhodin through the actinorhodin biosynthetic gene cluster activator ActII-orf4. GBL binding to AtrA prevents its binding to the promoter of the actII-orf4 gene, thereby disabling its transcription, while at the same time, GBL binding to ScbR causes coelimycin antibiotic synthesis derepression. ConclusionsThe opposite modes of action of ScbR (repressor) and AtrA (activator) have opposite effects upon GBL binding, activating coelimycin and blocking actinorhodin production at the same time. This phenomenon constitutes an elegant regulatory mechanism that ensures that coelimycin and actinorhodin production are mutually exclusive. These findings also suggest that quorum sensing must be taken into account when designing efficient antibiotic production processes and can be manipulated to ensure both better yield and specificity.

molecular biology↗