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Transcriptional and functional characterizations of multiple flagellin genes in spirochetes
Author(s) -
Kurniyati Kurni,
Chang Yunjie,
Liu Jun,
Li Chunhao
Publication year - 2022
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.14959
Subject(s) - flagellin , biology , flagellum , treponema denticola , gene , protein filament , microbiology and biotechnology , genetics , bacteria , porphyromonas gingivalis
The flagellar filament is a helical propeller for bacterial locomotion. In external flagellates, the filaments are mostly homopolymers of a single flagellin protein. By contrast, the flagellar filaments of spirochetes are mostly heteropolymers of multiple flagellin proteins. This report seeks to investigate the role of multiple flagellin proteins using the oral spirochete Treponema denticola as a model. First, biochemical and genetic studies uncover that the flagellar filaments of T. denticola mainly comprise four proteins, FlaA, FlaB1, FlaB2, and FlaB3, in a defined stoichiometry. Second, transcriptional analyses reveal that the genes encoding these four proteins are regulated by two different transcriptional factors, sigma 28 and sigma 70 . Third, loss‐of‐function studies demonstrate that each individual flagellin protein contributes to spirochete motility, but none of them is absolutely required. Last, we provide genetic and structural evidence that FlaA forms a “seam”‐like structure around the core and that deletion of individual flagellin protein alters the flagellar homeostasis. Collectively, these results demonstrate that T. denticola has evolved a unique mechanism to finely regulate its flagellar filament gene expression and assembly which renders the organelle with the right number, shape, strength, and structure for its distinct motility.