Metabolic adaptation of Acinetobacter baumannii - role of phospholipids in nutrition and infection

膜质环境被各种鲍曼不动杆菌定植，这就提出了鲍曼不动杆菌如何使其代谢适应宿主环境的问题。磷脂酰胆碱（PC）和磷脂酰乙醇胺（PE）是人类细胞膜中最丰富的磷脂，是碳和能量来源的良好候选者。磷酸甘油脂的降解是由一系列不同的磷脂酶促进的。磷脂酶还调节细菌膜的磷脂组成，这对真核宿主细胞的免疫防御系统的生存至关重要。因此，磷脂酶在病理生物学中起着关键作用。在我们之前的研究中，我们已经在鲍曼不动杆菌中发现了三种磷脂酶D （PLDs）和两种磷脂酶C (plc)，它们协同作用于大黄蜂毛虫和肺上皮细胞的侵袭。接下来，我们将对pld进行纯化和生化表征，以揭示其作用模式。此外，我们将讨论PLDs的亚细胞定位和调控。我们发现了胆碱和甜菜碱的多个不依赖渗透的BCC转运体，这表明BCCTs除了渗透保护外还有其他作用。一个可能是胆碱作为能量来源的作用，正如我们在巴莱草中发现的那样。我们将通过突变体研究和肺上皮细胞培养来解决胆碱和甜菜碱摄取在宿主适应中的作用。分析了胆碱和甜菜碱作为潜在碳源或氮源的作用。此外，胆碱和甘氨酸甜菜碱作为调节代谢物的作用将引发对富含胆碱的宿主环境的“感知”，从而导致毒力因子的转录调节。我们还在鲍曼不动杆菌中发现了多种心磷脂（CL）和单心磷脂（MLCL）。后者在细菌中很少被检测到。已知CLs在致病菌的毒力中起重要作用，但mlcl的功能尚不清楚。我们发现PLD2和PLD3对于CL和MLCL的生产都是必不可少的。接下来，我们将研究PLD2-和pld3介导的CL和MLCL的合成。此外，我们的目的是阐明CL和MLCL在鲍曼不动杆菌两种膜中的分布。细菌的膜脂组成随着环境的变化而变化。我们将分析宿主感染对pld表达和pld产生的影响。此外，将讨论PLD2和PLD3过量产生对毒力的影响。我们的工作假设是，各种各样的CLs和mlcl在脂质a调节中发挥作用，从而有助于人类宿主的适应和持久性。我们将通过比较鲍曼不动杆菌pld2/pld3突变体和野生型细胞中与脂质A相关的脂肪酸，分析CL和MLCL在脂质A调节中的作用。

Membranous environments are colonized by various strains of A. baumannii, which raises the question on how A. baumannii manages to adapt its metabolism to the host environment. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are the most abundant phospholipids found in human cell membranes and make them good candidates as carbon and energy source. The degradation of phosphoglycerolipids is facilitated by a set of different phospholipases. Phospholipases also modulate the phospholipid composition of bacterial membranes, which is crucial to survive the immune defence system of eukaryotic host cells. Therefore, phospholipases play a key role in pathobiology. In our preceding studies we have identified three phospholipases D (PLDs) and two phospholipases C (PLCs) in A. baumannii acting in concerted manner in invasion of G. mellonella caterpillars and lung epithelial cells. Next, we will purify and biochemically characterize the PLDs to unravel their mode of action. Moreover, we will address the subcellular localization and regulation of the PLDs. We identified multiple osmo-independent BCC transporter for choline and glycine betaine which suggests an additional role of the BCCTs other than osmostress protection. One could be a role of choline as energy source as we have found in A. baylyi. We will address the role of choline and glycine betaine uptake in host adaptation by mutant studies in G. mellonella and in lung epithelial cell cultures. The role of choline and glycine betaine as potential carbon or nitrogen source will also be analyzed. Moreover, a role of choline and glycine betaine as regulatory metabolites triggering the "sensing" of choline rich host environments thereby leading to transcriptional modulation of virulence factors will be addressed. We have also identified a broad variety of cardiolipins (CL) and monolysocardiolipins (MLCL) in A. baumannii. The latter has been very rarely detected in bacteria. CLs are known to play important roles in virulence of pathogenic bacteria whereas the function of MLCLs is unclear. We found that PLD2 and PLD3 are both essential for CL and MLCL production. Next, we will investigate the PLD2- and PLD3-mediated synthesis of CL and MLCL. Moreover, we aim to elucidate the distribution of CL and MLCL in both membranes of A. baumannii. Membrane lipid composition of bacteria changes in response to environmental changes. We will analyze the effect of host infection on pld expression and PLD production. Moreover, the effect of PLD2 and PLD3 overproduction on virulence will be addressed. Our working hypothesis is that the large variety of CLs and MLCLs plays a role of lipid A modulation thereby contributing to adaptation and persistence in the human host. We will analyze the role of CL and MLCL in lipid A modulation by comparison of fatty acids linked to lipid A in A. baumannii pld2/pld3 mutants and in wildtype cells.