The outer membrane (OM) of Gram-negative bacteria is a selective permeability barrier that allows uptake of nutrients while simultaneously protecting the cell from harmful compounds. The basic pathways and molecular machinery responsible for transporting lipopolysaccharides (LPS), lipoproteins, and β-barrel proteins to the OM have been identified, but very little is known about phospholipid (PL) transport. To identify genes capable of affecting PL transport, we screened for genetic interactions with mlaA*, a mutant in which anterograde PL transport causes the inner membrane (IM) to shrink and eventually rupture; characterization of mlaA*-mediated lysis suggested that PL transport can occur via a high-flux diffusive flow mechanism. We found that YhdP, an IM protein involved in maintaining the OM permeability barrier, modulates the rate of PL transport during mlaA*-mediated lysis. Deletion of yhdP from mlaA* reduced the rate of IM transport to the OM by 50%, slowing shrinkage of the IM and delaying lysis. As a result, the weakened OM of ∆yhdP cells was further compromised and ruptured before the IM during mlaA*-mediated death. These findings demonstrate the existence of a high-flux diffusive pathway for PL flow in Escherichia coli that is modulated by YhdP.

革兰氏阴性细菌的外膜（OM）是选择性渗透屏障，可吸收营养，同时保护细胞免受有害化合物的侵害。已经确定了负责将脂多糖（LPS），脂蛋白和β-桶蛋白转运至OM的基本途径和分子机制，但对磷脂（PL）转运的了解却很少。为了鉴定能够影响PL转运的基因，我们筛选了与mlaA *的遗传相互作用，mlaA *是顺向PL转运导致内膜（IM）收缩并最终破裂的突变体。表征MLAA*介导的裂解表明PL转运可通过高通量扩散流机制发生。我们发现，YhdP，一种参与维持OM渗透屏障的IM蛋白，可在mlaA *介导的裂解过程中调节PL转运的速率。从mlaA *中删除yhdP使IM向OM的转运速率降低了50％，减缓了IM的收缩并延迟了裂解。结果，在mlaA *介导的死亡期间，IM之前，ΔyhdP细胞弱化的OM进一步受损并破裂。这些发现证明存在由YhdP调节的大肠杆菌PL流高通量扩散途径。