Sphingosine Kills Bacteria by Binding to Cardiolipin

Sphingosine is a long-chain sphingoid base that has been shown to have bactericidal activity against many pathogens, including , and We have previously demonstrated that sphingosine is present in nasal, tracheal, and bronchial epithelial cells and constitutes a central element of the defense of the airways against bacterial pathogens. Here, using assorted lipid-binding and cell biology assays, we demonstrate that exposing and cells to sphingosine results in a very rapid, within minutes, permeabilization of the bacterial plasma membrane, resulting in leakiness of the bacterial cells, loss of ATP, and loss of bacterial metabolic activity. These alterations rapidly induced bacterial death. Mechanistically, we demonstrate that the presence of the protonated NH group in sphingosine, which is an amino-alcohol, is required for sphingosine's bactericidal activity. We also show that the protonated NH group of sphingosine binds to the highly negatively-charged lipid cardiolipin in bacterial plasma membranes. Of note, this binding was required for bacterial killing by sphingosine, as revealed by genetic experiments indicating that or strains that lack cardiolipin synthase are resistant to sphingosine, both and We propose that binding of sphingosine to cardiolipin clusters cardiolipin molecules in the plasma membrane of bacteria. This clustering results in the formation of gel-like or even crystal-like structures in the bacterial plasma membrane and thereby promotes rapid permeabilization of the plasma membrane and bacterial cell death.