Institute of Medical Microbiology and Hygiene, Dresden University of Technology, Fetscherstr. 74, D-01307 Dresden, Germany.
Institute of Microbiology, Dresden University of Technology, Helmholtzstr. 10, D-01062 Dresden, Germany.
Microbiology (Reading). 2010 Oct;156(Pt 10):2953-2961. doi: 10.1099/mic.0.039933-0. Epub 2010 Jul 23.
Phase-variable expression of Legionella pneumophila lipopolysaccharide (LPS) has not been described in detail for strains possessing the virulence-associated epitope recognized by the monoclonal antibody (mAb) 3/1 of the Dresden Panel. About 75 % of cases of community-acquired legionellosis are caused by mAb 3/1-positive strains. In this study, the LPS architecture of the mAb 3/1-positive Corby strain was investigated during its life cycle in broth culture and inside monocytic host cells. During the exponential growth phase in broth, the highly acetylated and therefore strongly hydrophobic mAb 3/1 epitope is expressed continuously, but only 3 % of the bacteria can be detected using mAb 59/1, which recognizes a short-chain variant of the Legionella LPS that is less hydrophobic due to missing acetylations of the O-chain. The percentage of mAb 59/1-positive legionellae increases up to 34 % in the post-exponential growth phase. LPS shed in broth during the exponential phase is mAb 59/1-negative, and mAb 3/1-positive components do not possess short-chain molecules. The LPS pattern expressed and shed inside U937 cells and A/J mouse macrophages points to the same regulatory mechanisms. During the so-called 'pregnant pause', the period for establishment of the replicative phagosomes, the mAb 3/1-positive LPS is shed into the phagosome and seems to pass through the phagosomal membrane, while mAb 59/1-positive LPS is detectable only on the bacterial surface. After egress of the legionellae into the cytoplasm followed by host cell lysis, individual bacteria are mAb 3/1-positive and mAb 59/1-negative. Intracellularly formed Legionella clusters consist of surface-located mAb 3/1-positive bacteria, which are predominantly mAb 59/1-negative. They surround less hydrophobic and therefore closely packed mAb 59/1-positive bacteria. Based on the different degrees of hydrophobicity, bacteria are able to support the expression of two functionally different LPS architectures, namely more hydrophobic LPS for surviving in aerosols and more hydrophilic LPS for close-packing of legionellae inside clusters.
军团菌脂多糖（LPS）的阶段变异性表达尚未详细描述具有多克隆抗体（mAb）3/1 识别的毒力相关表位的菌株。大约 75%的社区获得性军团病是由 mAb 3/1 阳性菌株引起的。在这项研究中，研究了 mAb 3/1 阳性 Corby 菌株在肉汤培养和单核宿主细胞内的生命周期中的 LPS 结构。在肉汤的指数生长阶段，高度乙酰化且因此具有强疏水性的 mAb 3/1 表位连续表达，但只能用 mAb 59/1 检测到 3%的细菌，mAb 59/1 识别由于 O-链缺少乙酰化而疏水性较低的短链变体的 Legionella LPS。在指数生长后期，mAb 59/1 阳性的军团菌增加到 34%。指数期在肉汤中脱落的 LPS 是 mAb 59/1 阴性的，mAb 3/1 阳性的成分不具有短链分子。在 U937 细胞和 A/J 鼠巨噬细胞中表达和脱落的 LPS 模式表明存在相同的调控机制。在所谓的“怀孕暂停”期间，即建立复制性吞噬体的时期，mAb 3/1 阳性 LPS 脱落到吞噬体中，似乎穿过吞噬体膜，而 mAb 59/1 阳性 LPS 只能在细菌表面检测到。在军团菌进入细胞质并导致宿主细胞裂解后，个别细菌是 mAb 3/1 阳性和 mAb 59/1 阴性。细胞内形成的军团菌簇由表面定位的 mAb 3/1 阳性细菌组成，这些细菌主要是 mAb 59/1 阳性。它们围绕着疏水性较低且因此紧密堆积的 mAb 59/1 阳性细菌。基于不同程度的疏水性，细菌能够支持两种功能不同的 LPS 结构的表达，即在气溶胶中生存的更疏水性 LPS 和在簇内紧密包装的军团菌的更亲水性 LPS。
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