International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
Institute of Crystallography, CNR, Trieste, Italy.
mSphere. 2021 Mar 31;6(2):e01322-20. doi: 10.1128/mSphere.01322-20.
LuxR solos are related to quorum sensing (QS) LuxR family regulators; however, they lack a cognate LuxI family protein. LuxR solos are widespread and almost exclusively found in proteobacteria. In this study, we investigated the distribution and conservation of LuxR solos in the fluorescent pseudomonads group. Our analysis of more than 600 genomes revealed that the majority of fluorescent spp. carry one or more LuxR solos, occurring considerably more frequently than complete LuxI/LuxR archetypical QS systems. Based on the adjacent gene context and conservation of the primary structure, nine subgroups of LuxR solos have been identified that are likely to be involved in the establishment of communication networks. Modeling analysis revealed that the majority of subgroups shows some substitutions at the invariant amino acids of the ligand-binding pocket of QS LuxRs, raising the possibility of binding to non-acyl-homoserine lactone (AHL) ligands. Several mutants and gene expression studies on some LuxR solos belonging to different subgroups were performed in order to shed light on their response. The commonality of LuxR solos among fluorescent pseudomonads is an indication of their important role in cell-cell signaling. Cell-cell communication in bacteria is being extensively studied in simple settings and uses chemical signals and cognate regulators/receptors. Many Gram-negative proteobacteria use acyl-homoserine lactones (AHLs) synthesized by LuxI family proteins and cognate LuxR-type receptors to regulate their quorum sensing (QS) target loci. AHL-QS circuits are the best studied QS systems; however, many proteobacterial genomes also contain one or more LuxR solos, which are QS-related LuxR proteins which are unpaired to a cognate LuxI. A few LuxR solos have been implicated in intraspecies, interspecies, and interkingdom signaling. Here, we report that LuxR solo homologs occur considerably more frequently than complete LuxI/LuxR QS systems within the group of species and that they are characterized by different genomic organizations and primary structures and can be subdivided into several subgroups. The group consists of more than 50 species, many of which are found in plant-associated environments. The role of LuxR solos in cell-cell signaling in fluorescent pseudomonads is discussed.
LuxR 孤子与群体感应 (QS) LuxR 家族调节剂有关；然而，它们缺乏同源 LuxI 家族蛋白。LuxR 孤子广泛存在，几乎只存在于变形菌中。在这项研究中，我们调查了荧光假单胞菌组中 LuxR 孤子的分布和保守性。我们对超过 600 个基因组的分析表明，大多数荧光 spp. 携带一个或多个 LuxR 孤子，其出现频率明显高于完整的 LuxI/LuxR 典型 QS 系统。基于相邻基因的上下文和主要结构的保守性，已经确定了九个 LuxR 孤子亚组，它们可能参与建立通信网络。建模分析表明，大多数亚组在 QS LuxR 的配体结合口袋的不变氨基酸处显示出一些取代，这增加了与非酰基-高丝氨酸内酯 (AHL) 配体结合的可能性。为了阐明它们的反应，对属于不同亚组的一些 LuxR 孤子的突变体和基因表达研究进行了一些研究。荧光假单胞菌中 LuxR 孤子的普遍性表明它们在细胞间信号传递中具有重要作用。细菌之间的细胞间通讯正在简单的环境中进行广泛研究，并使用化学信号和同源调节剂/受体。许多革兰氏阴性变形菌使用由 LuxI 家族蛋白合成的酰基-高丝氨酸内酯 (AHL) 和同源 LuxR 型受体来调节它们的群体感应 (QS) 靶标基因座。AHL-QS 电路是研究最充分的 QS 系统；然而，许多变形菌基因组还包含一个或多个 LuxR 孤子，它们是与同源 LuxI 配对的 QS 相关 LuxR 蛋白。一些 LuxR 孤子已被牵连到种内、种间和种间信号传递中。在这里，我们报告说，在 物种组中，LuxR 孤子同源物的出现频率明显高于完整的 LuxI/LuxR QS 系统，并且它们具有不同的基因组组织和主要结构，可以细分为几个亚组。该组由 50 多种物种组成，其中许多存在于植物相关环境中。讨论了 LuxR 孤子在荧光假单胞菌细胞间信号传递中的作用。
