Instituto de Biotecnología y Biología Molecular (IBBM), Facultad de Ciencias Exactas, Universidad Nacional de La Plata y CCT-La Plata, CONICET, La Plata, Argentina.
Laboratorio de Genética, Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata, La Plata, Argentina.
J Bacteriol. 2021 Mar 8;203(7). doi: 10.1128/JB.00403-20.
, the N-fixing symbiont of soybean, has two independent flagellar systems: a single subpolar flagellum and several lateral flagella. Each flagellum is a very complex organelle composed of 30 to 40 different proteins located inside and outside the cell whereby flagellar gene expression must be tightly controlled. Such control is achieved by a hierarchy of regulators that ensure the timing of synthesis and the allocation of the different flagellar substructures. Previously, we analyzed the gene organization, expression, and function of the lateral flagellar system. Here, we studied the role of the response regulator FlbD and its -acting regulator FliX in the regulation of subpolar flagellar genes. We found that the LP-ring, distal rod, and hook of the subpolar flagellum were tightly controlled by FlbD and FliX. Furthermore, we obtained evidence for the existence of cross-regulation between these gene products and the expression of LafR, the master regulator of lateral flagella. In addition, we observed that extracellular polysaccharide production and biofilm formation also responded to these flagellar regulators. In this regard, FlbD might contribute to the switch between the planktonic and sessile states. Most environmental bacteria switch between two free-living states: planktonic, in which individual cells swim propelled by flagella, and sessile, in which bacteria form biofilms. Apart from being essential for locomotion, the flagellum has accessory functions during biofilm formation. The synthesis of flagella is a highly regulated process, and coordination with accessory functions requires the interconnection of various regulatory networks. Here, we show the role of class II regulators involved in the synthesis of the subpolar flagellum and their possible participation in cross-regulation with the lateral flagellar system and exopolysaccharide production. These findings highlight the coordination of the synthetic processes of external structures, such as subpolar and lateral flagella, with exopolysaccharides, which are the main component of the biofilm matrix.
大豆的固氮共生体，有两个独立的鞭毛系统：一个单一的亚极鞭毛和几个侧鞭毛。每个鞭毛都是一个非常复杂的细胞器，由 30 到 40 种不同的蛋白质组成，位于细胞内外，鞭毛基因的表达必须受到严格控制。这种控制是通过一个层次的调节剂来实现的，这些调节剂确保了不同鞭毛亚结构的合成和分配的时间。以前，我们分析了侧鞭毛系统的基因组织、表达和功能。在这里，我们研究了响应调节剂 FlbD 和其-作用调节剂 FliX 在亚极鞭毛基因调节中的作用。我们发现，亚极鞭毛的 LP 环、远端杆和钩受到 FlbD 和 FliX 的严格控制。此外，我们还获得了这些基因产物与侧鞭毛的主调节剂 LafR 表达之间存在交叉调节的证据。此外，我们观察到细胞外多糖的产生和生物膜的形成也对这些鞭毛调节剂有反应。在这方面，FlbD 可能有助于浮游和固着状态之间的转换。大多数环境细菌在两种自由生活状态之间切换：浮游状态，在这种状态下，单个细胞在鞭毛的推动下游动；固着状态，在这种状态下，细菌形成生物膜。除了对运动是必不可少的，鞭毛在生物膜形成过程中还有辅助功能。鞭毛的合成是一个高度调节的过程，与辅助功能的协调需要各种调节网络的互联。在这里，我们展示了参与亚极鞭毛合成的 II 类调节剂的作用，以及它们与侧鞭毛系统和细胞外多糖产生的可能交叉调节作用。这些发现强调了外部结构（如亚极鞭毛和侧鞭毛）与细胞外多糖的合成过程的协调，细胞外多糖是生物膜基质的主要成分。
