Indole is a critical bacterial signaling molecule, which is known to influence various cellular processes, including biofilm formation or maintenance and antibiotic resistance. In an effort to better understand and quantify the mechanistic influences of indole, we examined the membrane-specific interactions of indole in various strains of Gram-negative bacteria. Specifically, we employed the surface sensitive nonlinear optical technique, time-resolved second-harmonic light scattering (SHS) to characterize variations in the membrane transport behavior of the cationic dye, malachite green (MG), in the presence of physiologically relevant concentrations of extracellular indole (i.e., 0-1.5 mM). For E. coli (which is capable of producing indole), our results reveal a dramatic increase in the membrane permeability of both the outer membrane (OM) and the inner cytoplasmic membrane (CM). Conversely, for P. aeruginosa (which is incapable of producing indole, but needs to uptake indole from the extracellular environment), our results showed absolutely no change in the OM transport behavior, but a slight change in the permeability of the CM. Additionally, a series of control experiments with unilamellar liposomes (composed entirely of lipids isolated from the membranes of E. coli) revealed that the MG transport rate was completely independent of the relative presence of indole. Given that the liposomes specifically lacked protein of any kind, suggests that the indole-induced enhancement of membrane permeability observed in bacteria likely stems from an indole-protein interaction.

Extracellular signaling molecule indole increases permeability of bacterial membranes

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.