Fulano Alex M, Shen Danyu, Zhang En-Hui, Shen Xi, Chou Shan-Ho, Minamino Tohru, Puopolo Gerardo, Qian Guoliang
College of Plant Protection (Laboratory of Plant Immunity; Key Laboratory of Integrated Management of Crop Diseases and Pests), Nanjing Agricultural University, Nanjing 210095, PR China.
Institute of Biochemistry, and NCHU Agricultural Biotechnology Center, National Chung Hsing University, Taichung, Taiwan, ROC.
Comput Struct Biotechnol J. 2020 Nov 10;18:3368-3376. doi: 10.1016/j.csbj.2020.10.029. eCollection 2020.
The lack of functional flagella and the ability to prey upon other microorganisms are well-known traits of , a plant beneficial bacterial species. Here, we report a possible link between these two traits in the model strain OH11 (OH11). The genome of OH11 encompasses several homologous genes involved in the flagellum formation but it lacks a functional , encoding the flagellin. Despite the lack of the main component of the flagellum, OH11 genome includes genes involved in the flagellar type III secretion system (FT3SS), which is commonly deployed by flagellated bacteria to transport flagellar subunit proteins. To understand the role played by FT3SS in OH11, we showed that the remaining FT3SS genes were expressed under laboratory conditions. Subsequently, we showed that the identified FT3SS genes involved in the secretion of the hook-capping protein FlgD, suggesting OH11 likely possessed a functional FT3SS system. Blocking FT3SS in OH11 via inactivation of the ATPase FliI impaired the secretion of the proteins Le3970 (protease), Le4493 (ß-1,3-glucanase A) and Le1659 (halo acid dehalogenase family), that showed a toxic activity against the yeast . The possible link between FT3SS and OH11 antagonism towards was also confirmed by loss of toxicity in both mutants of Δ and Δ that lacks the FT3SS structural gene when co-cultured with the yeast strain. The design of synthetic proteins toxic against the Gram-negative bacterium further supported the involvement of FT3SS in the ability of OH11 to parasitize other microorganisms. Overall, these results revealed a possible cooption of components of FT3SS system in the competition with other microorganisms in the plant beneficial bacterium OH11 and highlighted a functional divergence of FT3SS between flagellated and non-flagellated bacteria.
缺乏功能性鞭毛以及捕食其他微生物的能力是植物有益细菌物种——[具体物种名称缺失]的众所周知的特征。在此，我们报告了模式菌株OH11中这两个特征之间的可能联系。OH11的基因组包含几个参与鞭毛形成的同源基因，但它缺乏一个编码鞭毛蛋白的功能性[具体基因名称缺失]。尽管缺乏鞭毛的主要成分，但OH11基因组包含参与鞭毛III型分泌系统（FT3SS）的基因，鞭毛细菌通常利用该系统运输鞭毛亚基蛋白。为了了解FT3SS在OH11中所起的作用，我们表明其余的FT3SS基因在实验室条件下表达。随后，我们表明所鉴定的FT3SS基因参与了钩帽蛋白FlgD的分泌，这表明OH11可能拥有一个功能性的FT3SS系统。通过使ATP酶FliI失活来阻断OH11中的FT3SS，会损害Le3970（蛋白酶）、Le4493（β-1,3-葡聚糖酶A）和Le1659（卤代酸脱卤酶家族）的分泌，这些蛋白对酵母[具体酵母名称缺失]显示出毒性活性。当与酵母菌株共培养时，缺乏FT3SS结构基因[具体基因名称缺失]的Δ[具体缺失基因名称]和Δ[具体缺失基因名称]这两个突变体的毒性丧失，也证实了FT3SS与OH11对[具体酵母名称缺失]的拮抗作用之间的可能联系。针对革兰氏阴性细菌[具体细菌名称缺失]设计具有毒性的合成蛋白，进一步支持了FT3SS参与OH11寄生其他微生物的能力。总体而言，这些结果揭示了在植物有益细菌OH11与其他微生物竞争中，FT3SS系统的成分可能被共同利用，并突出了有鞭毛和无鞭毛细菌之间FT3SS的功能差异。
