Bacterial flagella are rotating nanomachines required for motility. Flagellar gene expression and protein secretion are coordinated for efficient flagellar biogenesis. Polar flagellates, unlike peritrichous bacteria, commonly order flagellar rod and hook gene transcription as a separate step after production of the MS ring, C ring, and flagellar type III secretion system (fT3SS) core proteins that form a competent fT3SS. Conserved regulatory mechanisms in diverse polar flagellates to create this polar flagellar transcriptional program have not been thoroughly assimilated. Using in silico and genetic analyses and our previous findings in Campylobacter jejuni as a foundation, we observed a large subset of Gram-negative bacteria with the FlhF/FlhG regulatory system for polar flagellation to possess flagellum-associated two-component signal transduction systems (TCSs). We present data supporting a general theme in polar flagellates whereby MS ring, rotor, and fT3SS proteins contribute to a regulatory checkpoint during polar flagellar biogenesis. We demonstrate that Vibrio cholerae and Pseudomonas aeruginosa require the formation of this regulatory checkpoint for the TCSs to directly activate subsequent rod and hook gene transcription, which are hallmarks of the polar flagellar transcriptional program. By reprogramming transcription in V. cholerae to more closely follow the peritrichous flagellar transcriptional program, we discovered a link between the polar flagellar transcription program and the activity of FlhF/FlhG flagellar biogenesis regulators in which the transcriptional program allows polar flagellates to continue to produce flagella for motility when FlhF or FlhG activity may be altered. Our findings integrate flagellar transcriptional and biogenesis regulatory processes involved in polar flagellation in many species.IMPORTANCE Relative to peritrichous bacteria, polar flagellates possess regulatory systems that order flagellar gene transcription differently and produce flagella in specific numbers only at poles. How transcriptional and flagellar biogenesis regulatory systems are interlinked to promote the correct synthesis of polar flagella in diverse species has largely been unexplored. We found evidence for many Gram-negative polar flagellates encoding two-component signal transduction systems with activity linked to the formation of flagellar type III secretion systems to enable production of flagellar rod and hook proteins at a discrete, subsequent stage during flagellar assembly. This polar flagellar transcriptional program assists, in some manner, the FlhF/FlhG flagellar biogenesis regulatory system, which forms specific flagellation patterns in polar flagellates in maintaining flagellation and motility when activity of FlhF or FlhG might be altered. Our work provides insight into the multiple regulatory processes required for polar flagellation.

中文翻译：

---

在不同的鞭毛虫中广泛保存由不同的两组分信号转导系统和基础鞭毛蛋白介导的极鞭毛转录程序。

细菌鞭毛是运动所需的旋转纳米机器。鞭毛基因表达和蛋白质分泌被协调为有效的鞭毛生物发生。与鞭毛细菌不同，极性鞭毛通常在产生MS环，C环和III型鞭毛分泌系统（fT3SS）核心蛋白（形成有效的fT3SS）后，单独命令鞭毛杆和钩基因转录。在创建这种极性鞭毛转录程序的各种极性鞭毛中保守的调节机制尚未被完全吸收。利用计算机分析和遗传分析以及我们先前在空肠弯曲杆菌中的发现作为基础，我们观察到带有FlhF / FlhG调节系统的革兰氏阴性细菌的很大一部分，用于极性鞭毛，具有与鞭毛相关的两成分信号转导系统（TCS）。我们目前的数据支持极鞭毛中的一般主题，其中MS环，转子和fT3SS蛋白在极鞭毛生物发生过程中有助于调节性检查点。我们证明霍乱弧菌和铜绿假单胞菌需要为TCSs形成此监管检查站，以直接激活后续的杆和钩基因转录，这是极鞭毛转录程序的标志。通过对霍乱弧菌中的转录进行重新编程，使其更紧密地遵循周游性鞭毛转录程序，我们发现极性鞭毛转录程序与FlhF / FlhG鞭毛生物发生调节因子的活性之间存在联系，其中当FlhF或FlhG活性可能改变时，转录程序允许极性鞭毛继续为运动产生鞭毛。我们的发现整合了鞭毛转录和生物发生调控过程，涉及许多物种的极鞭毛。转录和鞭毛生物发生调控系统如何相互连接以促进极性鞭毛在不同物种中的正确合成，目前尚未得到广泛的研究。我们发现了许多革兰氏阴性极性鞭毛虫的证据，这些鞭毛虫编码两组分信号转导系统，其活性与鞭毛III型分泌系统的形成有关，从而能够在鞭毛组装过程的不连续的后续阶段产生鞭毛杆和钩蛋白。该极性鞭毛转录程序以某种方式辅助FlhF / FlhG鞭毛生物发生调控系统，当FlhF或FlhG的活性可能发生改变时，它会在极性鞭毛中形成特定的鞭毛模式，从而维持鞭毛和运动。我们的工作深入了解了极鞭毛形成所需要的多种调控过程。