A Fluorescent Probe Distinguishes between Inhibition of Early and Late Steps of Lipopolysaccharide Biogenesis in Whole Cells

Lipopolysaccharide (LPS) biogenesis in Gram-negative organisms involves its biosynthesis in the cytoplasm and subsequent transport across three cellular compartments to the cell surface. We developed a fluorescent probe that allows us to determine the spatial distribution of LPS in whole cells. We show that polymyxin B nonapeptide (PMBN) containing a dansyl fluorophore specifically binds to LPS in membranes. We show that this probe detects decreases in LPS levels on the cell surface when LPS biosynthesis is inhibited at an early step. We also can detect accumulation of LPS in particular subcellular locations when LPS assembly is blocked during transport, allowing us to differentiate inhibitors targeting early and late stages of LPS biogenesis.