The Cell Envelope of the Multi-Drug Resistant Pathogen Acinetobacter baumannii

细菌的细胞包膜是一个显著的和复杂的结构，保护细菌免受周围环境的影响。革兰氏阴性菌的一个决定性特征是存在外膜（OM），该外膜包裹着这些生物的肽聚糖层。虽然内膜（IM）由甘油磷脂（GPL）组成，但内膜是一个脂质极端不对称的双层，GPL局限于内小叶，脂多糖（LPS）局限于外小叶。这种独特的膜组织为革兰氏阴性细菌提供了保护，使其免受大分子极性以及亲脂性化合物的侵害，成为抵抗各种抗生素和有毒化合物的基本天然屏障。值得注意的是，高优先级的革兰氏阴性病原体鲍曼不动杆菌可以完全灭活LPS生物合成，作为对“最后手段”抗生素多粘菌素耐药的另一种机制。本应用程序的主要目的是研究鲍曼不动杆菌在不考虑LPS状态的情况下维持细胞包膜所需的机制。虽然不对称OM相对于GPL双分子层的好处是显而易见的，因为它提供了不可渗透的屏障，但鲍曼不动杆菌缺乏LPS的必要性可以用作探索存在或不存在LPS的OM稳定性新机制的工具。在Aim 1中，我们将研究细菌从LPS缺陷细胞向LPS阳性细胞转变过程中的变化，包括GPL转运如何影响LPS结构。对于Aim 2，我们的重点将是鉴定支持脂多糖缺乏的基因，包括脂蛋白的作用以及无论脂多糖状态如何，它们如何运输到细胞表面。最后，在Aim 3中，我们将描述通过遗传和化学合成致死筛选发现的lps阳性鲍曼不动杆菌OM稳定性所需的新基因产物。鉴于目前的文献，该应用程序建立在强有力的科学前提上，解决了我们对鲍曼芽胞杆菌包膜和其他革兰氏阴性病原体理解的主要差距。此外，Aims重点关注影响膜生物发生，细菌发病机制和抗菌药物发展的高度保守途径。

The bacterial cell envelope is a remarkable and complex structure that guards bacteria from their surrounding environment. A defining feature of Gram-negative bacteria is the presence of an outer membrane (OM) that encapsulates the peptidoglycan layer of these organisms. While the inner membrane (IM) is composed of glycerophospholipids (GPLs), the OM is a bilayer with extreme lipid asymmetry with GPL confined to the inner leaflet and lipopolysaccharide (LPS) localized to the outer leaflet. This unique membrane organization affords Gram-negative bacteria protection from large polar molecules, as well as lipophilic compounds, serving as an essential innate barrier to a variety of antibiotics and toxic compounds. Remarkably, the high-priority Gram-negative pathogen Acinetobacter baumannii can completely inactivate LPS biosynthesis as an alternative mechanism of resistance to the “last-resort” antibiotics called polymyxins. The primary objective of this application is to investigate the mechanisms required for maintenance of the cell envelope of A. baumannii, regardless of LPS status. While the benefit of an asymmetric OM relative to a GPL bilayer is apparent due to the impermeable barrier it provides, the lack of LPS essentiality in A. baumannii can be used a tool to explore novel mechanisms of OM stability in both the presence or absence of LPS. In Aim 1, we will investigate changes to the bacterium during its transition from an LPS-deficient to a LPS-positive cell, including how GPL transport influences LPS structure. For Aim 2 our focus will be the identification of genes that support LPS-deficiency, including the role of lipoproteins and how they are transported to the cell surface regardless of LPS status. Finally, in Aim 3, we will characterize novel gene products necessary for OM stability in LPS-positive A. baumannii uncovered by a genetic and chemical synthetic lethality screen. Given the current literature, the application is built on a strong scientific premise addressing major gaps in our understanding of the A. baumannii cell envelope and other Gram-negative pathogens. Furthermore, the Aims focus on highly conserved pathways that impact membrane biogenesis, bacterial pathogenesis, and antimicrobial development.