Sun Yu, Xie Zhihong, Sui Fu, Liu Xiaolin, Cheng Wuzeng
Key Laboratory of Coastal Biology and Bioresource Utilization, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, China.
College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China.
Front Microbiol. 2019 Apr 2;10:638. doi: 10.3389/fmicb.2019.00638. eCollection 2019.
Cbp1, a chemoreceptor containing a PilZ domain was identified in ORS571, a nitrogen-fixing free-living soil bacterium that induces nodule formation in both the roots and stems of the host legume . Chemoreceptors are responsible for sensing signals in the chemotaxis pathway, which guides motile bacteria to beneficial niches and plays an important role in the establishment of rhizobia-legume symbiosis. PilZ domain proteins are known to bind the second messenger c-di-GMP, an important regulator of motility, biofilm formation and virulence. Cbp1 was shown to bind c-di-GMP through the conserved RxxxR motif of its PilZ domain. A mutant strain carrying a deletion was impaired in chemotaxis, a feature that could be restored by genetic complementation. Compared with the wild type strain, the Δ mutant displayed enhanced aggregation and biofilm formation. The Δ mutant induced functional nodules when inoculated individually. However, the Δ mutant was less competitive than the wild type in competitive root colonization and nodulation. These data are in agreement with the hypothesis that the c-di-GMP binding chemoreceptor Cbp1 in is involved in chemotaxis and nodulation.
在ORS571（一种能在宿主豆科植物的根和茎中诱导根瘤形成的固氮自生土壤细菌）中鉴定出了Cbp1，它是一种含有PilZ结构域的化学感受器。化学感受器负责在趋化途径中感知信号，该途径引导运动性细菌到达有益的生态位，并在根瘤菌 - 豆科植物共生关系的建立中发挥重要作用。已知PilZ结构域蛋白可结合第二信使环二鸟苷酸（c-di-GMP），它是运动性、生物膜形成和毒力的重要调节因子。研究表明，Cbp1通过其PilZ结构域的保守RxxxR基序结合c-di-GMP。携带缺失突变的菌株在趋化性方面存在缺陷，这一特征可通过基因互补得以恢复。与野生型菌株相比，Δ突变体表现出增强的聚集和生物膜形成能力。单独接种时，Δ突变体可诱导形成功能性根瘤。然而，在竞争性根定殖和结瘤过程中，Δ突变体的竞争力低于野生型。这些数据与以下假设一致：ORS571中结合c-di-GMP的化学感受器Cbp1参与趋化作用和结瘤过程。
