Polar localization of putative phospholipid transporters in <i>Escherichia coli</i>

The Gram-negative bacterial cell envelope comprises an outer membrane (OM) with an asymmetric arrangement of lipopolysaccharides and phospholipids (PLs), protecting them from both physical and chemical threats. To build the OM, PLs must be transported across the cell envelope; this process has remained elusive until recently, where three collectively essential AsmA-superfamily proteins-YhdP, TamB, and YdbH-are proposed to function as anterograde PL transporters in <i>Escherichia coli</i>. Here, we identify the cell wall-binding protein DedD as a novel interacting partner of YhdP and discover that all three AsmA-superfamily proteins are recruited to and strongly enriched at the cell poles. Our observation raises the possibility that anterograde PL transport could be spatially restricted to the cell poles and highlights the importance of understanding the spatial-temporal regulation of OM biogenesis in coordination with cell growth and division.IMPORTANCEThe outer membrane (OM) of Gram-negative bacteria serves as an effective permeability barrier and confers intrinsic antibiotic resistance. This barrier function requires distinct distribution of lipids across the bilayer, yet how phospholipids, the most basic building block, get transported and assembled into the OM is not well understood. In this study, we describe the observation revealing that three putative phospholipid transporters are mostly present at the cell poles in <i>Escherichia coli</i>, highlighting possible polar localization of lipid transport to ultimately support OM biogenesis during growth and division. Our work sets the stage for studying how phospholipid transport impacts OM stability, lipid asymmetry, and/or function, thus informing future strategies for antibiotics development against these processes.