a Department of Biology and Biotechnology Charles Darwin , Sapienza University of Rome, Laboratory affiliated to Istituto Pasteur Italia - Fondazione Cenci Bolognetti , Rome , Italy.
b Department of Pharmacological and Biomolecular Sciences , University of Milan , Milan , Italy.
Virulence. 2018;9(1):1718-1733. doi: 10.1080/21505594.2018.1537730.
Lipopolysaccharide (LPS) is an essential structural component of the outer membrane (OM) of most Gram-negative bacteria. In the model organism Escherichia coli, LPS transport to the OM requires seven essential proteins (LptABCDEFG) that form a continuous bridge across the cell envelope. In Pseudomonas aeruginosa the recently-demonstrated essentiality of LptD and LptH, the P. aeruginosa LptA homologue, confirmed the crucial role of the Lpt system and, thus, of LPS in OM biogenesis in this species. Surprisingly, independent high-throughput transposon mutagenesis studies identified viable P. aeruginosa insertion mutants in the lptE gene, suggesting that it might be dispensable for bacterial growth. To test this hypothesis, we generated an lptE conditional mutant in P. aeruginosa PAO1. LptE depletion only slightly impairs P. aeruginosa growth in vitro. Conversely, LptE is important for cell envelope stability, antibiotic resistance and virulence in an insect model. Interestingly, the maturation and OM localization of LPS is only marginally affected in LptE-depleted cells, while the levels of the OM component LptD are strongly reduced. This suggests that P. aeruginosa LptE might not be directly involved in LPS transport, although it is clearly essential for the maturation and/or stability of LptD. While poor functionality of LptD caused by LptE depletion is somehow tolerated by P. aeruginosa, this has a high cost in terms of cell integrity, drug resistance and virulence, highlighting LptE function(s) as an interesting target to weaken P. aeruginosa defenses and reduce its infectivity.
脂多糖 (LPS) 是大多数革兰氏阴性菌外膜 (OM) 的基本结构组成部分。在模式生物大肠杆菌中，LPS 向 OM 的转运需要七个必需蛋白 (LptABCDEFG)，它们在细胞包膜中形成一个连续的桥。在铜绿假单胞菌中，最近证明 LptD 和 LptH 的必需性，即铜绿假单胞菌 LptA 的同源物，证实了 Lpt 系统的关键作用，因此也证实了 LPS 在该物种 OM 生物发生中的关键作用。令人惊讶的是，独立的高通量转座子诱变研究鉴定出了铜绿假单胞菌 lptE 基因中的存活插入突变体，这表明它可能对细菌生长不是必需的。为了验证这一假设，我们在铜绿假单胞菌 PAO1 中生成了一个 lptE 条件性突变体。LptE 缺失仅轻微影响铜绿假单胞菌的体外生长。相反，LptE 对细胞包膜稳定性、抗生素耐药性和昆虫模型中的毒力很重要。有趣的是，在 LptE 耗尽的细胞中，LPS 的成熟和 OM 定位仅受到轻微影响，而 OM 成分 LptD 的水平则大大降低。这表明铜绿假单胞菌 LptE 可能不直接参与 LPS 转运，尽管它显然对 LptD 的成熟和/或稳定性是必需的。虽然 LptE 耗尽导致 LptD 的功能不佳在某种程度上被铜绿假单胞菌耐受，但这对细胞完整性、耐药性和毒力有很高的代价，突出了 LptE 的功能作为一个有趣的目标，可以削弱铜绿假单胞菌的防御能力并降低其感染性。
