Interpretation of antimicrobial function of biosurfactant rhamnolipids using Trisodium 8-hydroxypyrene-1,3,6-trisulfonate-based fluorescent surfactants

Abstract

The wide use of antibiotics can lead to antimicrobial resistance. Biosurfactant rhamnolipids are not prone to induce antimicrobial resistance due to their potential to target microbial membranes in both bacteria and fungi. However, the membrane interaction of anionic rhamnolipids with microbials has never been visually observed. This study applied previously synthesized anionic fluorescent Trisodium 8-hydroxypyrene-1,3,6-trisulfonate (HPTS)-based surfactants, with hydrophobic tails from C8 to C18, to examine their interaction with the plant pathogen Alternaria alternata. The antifungal potency of the surfactants exhibited a positive correlation with the increase in hydrophobic chain length, culminating in C16, which demonstrated the highest activity. Subsequently, a modest reduction in potency was noted for the C18. Fluorescence microscopy confirmed the membrane targeting of HPTS-C16, and molecular dynamics simulations supported its specific membrane interaction. HPTS-C16 was notably more effective against spores than mycelium, consistent with its binding affinity. This research provides a fluorescent method to dissect the relationship between surfactant properties and microbial membrane characteristics, guiding the development of antimicrobials to combat resistance.