Signaling via LuxR solos in the insect pathogen Photorhabdus luminescens and the human pathogen Photorhabdus asymbiotica

众所周知，细菌通过小的可扩散分子进行交流，这一过程称为群体感应。最好理解的群体感应系统是那些使用酰化高丝氨酸内酯（AHLs）进行通信的系统。这些系统的原型由一个LuxI样阿勒合酶和一个感受信号的同源LuxR受体组成。然而，许多变形菌具有LuxR受体，但缺乏任何LuxI型合酶，因此这些受体被称为LuxR孤儿或独奏。Photorhabdus luminescens是一种昆虫病原细菌，共有39个LuxR solos，这是迄今为止在细菌中发现的最高数量之一。在之前的资助期间，我们发现其中一个LuxR solo，PluR，是一个新的细胞间通信系统的一部分。代替AHLs，PluR感测α-吡喃酮，称为吡喃酮（PPY），由吡喃酮合酶PpyS产生作为信号分子。PluR是LuxR solo的第一个例子，它感测到的群体感应信号不是阿勒。与昆虫和人类病原体密切相关的Photorhabdus asybiotica与PluR有一个密切的同源物，名为PauR，但缺乏LuxI和PpyS同源物。我们有第一个证据表明，PauR传感器二烷基间苯二酚（DAR）和它们的前体环己二酮（CHDs），而不是PPY和AHLs作为信号。因此，在本项目中，我们将研究天然宿主P. asybiotica中这种基于DAR/CHD的新型细胞间通讯系统。此外，我们将试图确定的氨基酸基序的信号结合域的PluR和PauR，使它们特异性PPY或DAR/CHD传感器，分别，并区分它们从阿勒传感器。此外，我们将研究PluR和PauR的DNA结合位点，以定义这些LuxR solo的特定DNA结合盒。除了含有推定的阿勒结合结构域的LuxR solos之外，发光假单胞菌中的大多数LuxR solos具有PAS 4结构域。我们知道PAS 4-LuxR solo Plu 2018/Plu 2019是一种新型的王国间信号系统的一部分，因为该信号存在于昆虫大蜡螟中。因此，我们的目标是在目前的项目提案中确定这种跨王国信号的化学性质。由于该项目中研究的所有LuxR solo都涉及致病性，并且在多种人类病原菌中具有同源物，因此它们可能在未来作为新型抗菌剂的靶标。

It is well recognised that bacteria communicate via small diffusible molecules, a process termed quorum sensing. The best understood quorum sensing systems are those that use acylated homoserine lactones (AHLs) for communication. The prototype of those systems consists of a LuxI-like AHL synthase and a cognate LuxR-receptor that senses the signal. However, many proteobacteria possess LuxR receptors yet lack any LuxI-type synthase, and thus these receptors are referred to as LuxR orphans or solos. Photorhabdus luminescens is an insect pathogenic bacterium that has a total of 39 LuxR solos, which is one of the highest numbers that has ever been found in bacteria. In the previous funding period we found that one of these LuxR solos, PluR, is part of a novel cell-cell communication system. Instead of AHLs, PluR senses alpha-pyrones, named photopyrones (PPYs), produced by the pyrone synthase PpyS as signaling molecules. PluR was the first example of a LuxR solo that senses a quorum sensing signal that is not an AHL. The closely related insect and human pathogen Photorhabdus asymbiotica has a close homologue to PluR, named PauR, but lacks LuxI as well as PpyS homologues. We have first evidence that PauR senses dialkylresorcinols (DARs) and their precursors cyclohexanediones (CHDs) instead of PPYs and AHLs as signal. In this project we will therefore investigate this novel DAR/CHD-based cell-cell communication system in the native host P. asymbiotica. Moreover, we will attempt to identify amino acid motifs in the signal-binding domain of PluR and PauR that make them specific PPY or DAR/CHD sensors, respectively, and that distinguish them from the AHL sensors. Additionally, we will investigate the DNA-binding site(s) of PluR and PauR to define a specific DNA-binding box of these LuxR solos. Besides LuxR solos that contain a putative AHL binding domain, the majority of the LuxR solos in P. luminescens have a PAS4 domain. We know that the PAS4-LuxR solo Plu2018/Plu2019 is part of a novel type of inter-kingdom signaling system, as the signal is present in the insect Galleria mellonella. We therefore aim to identify the chemical nature of this inter-kingdom signal in the current project proposal. As all the LuxR solos that are investigated in this project are involved in pathogenicity and have homologues in diverse human pathogenic bacteria, they might act as targets for novel antimicrobials in the future.