A pleiotropic role of FlaG in regulating the cell morphogenesis and flagellar homeostasis at the cell poles of Treponema denticola

Abstract

FlaG homologue has been found in several bacteria including spirochetes; however, its function is poorly characterised. In this report, we investigated the role of TDE1473, a putative FlaG, in the spirochete Treponema denticola, a keystone pathogen of periodontitis. TDE1473 resides in a large gene operon that is controlled by a σ70‐like promoter and encodes a putative FlaG protein of 123 amino acids. TDE1473 can be detected in the periplasmic flagella (PFs) of T. denticola, suggesting that it is a flagella‐associated protein. Consistently, in vitro studies demonstrate that the recombinant TDE1473 interacts with the PFs in a dose‐dependent manner and that such an interaction requires FlaA, a flagellar filament sheath protein. Deletion of TDE1473 leads to long and less motile mutant cells. Cryo‐electron tomography analysis reveal that the wild‐type cells have 2–3 PFs with nearly homogenous lengths (ranging from 3 to 6 μm), whereas the mutant cells have less intact PFs with disparate lengths (ranging from 0.1 to 9 μm). The phenotype of T. denticola TDE1473 mutant reported here is different from its counterparts in other bacteria, which provides insight into further understanding the role of FlaG in the regulation of bacterial cell morphogenesis and flagellation.

Prevalence of phase variable epigenetic invertons among host-associated bacteria

“…E. faecalis was grown in brain-heart infusion (BHI) broth or on BHI agar plates. B. fragilis and T. denticola were grown in tryptone-yeast extract-gelatin-volatile fatty acids-serum (TYGVS) medium at 37°C in an anaerobic chamber with 85% nitrogen, 5% hydrogen and 10% CO 2 as previously described ( 37 , 38 ). Escherichia coli DH5α was used for molecular cloning of hsdS sequences and grown in Luria–Bertani ( 39 ) broth or on LB agar plates as described ( 21 ).…”

Transcriptional and functional characterizations of multiple flagellin genes in spirochetes

“…relative to that of dnaK (TDE0628), a housekeeping gene of T. denticola, using quantitative reverse transcription-PCR (qRT-PCR), as previously documented (Kurniyati et al, 2019). The flaA gene was constantly expressed and not affected by the growth phase, whereas the three flaB genes were actively expressed at the middle log phase, and then flaB2 and flaB3 started to decline at the late log phase, as did flaB1 at the stationary phase (Figure 3), suggesting that the expression of the three flagellin genes is affected by the growth phase of T. denticola.…”

“…(b) co-RT-PCR analysis. This experiment was performed as previously documented (Kurniyati et al, 2019). Five pairs of primers that bridge flaA and its upstream genes were designed and used for co-RT-PCR.…”

3D cryo-EM imaging of bacterial flagella: Novel structural and mechanistic insights into cell motility

“…The function of FlaA is not completely understood, but ΔflaA knockout mutants present motility defects (93,97,98), and normal filament assembly can be severely impaired (99). Besides FlaAs, additional protein species can be recruited onto the filament sheath of several Spirochetes (94,(99)(100)(101)(102)(103). Improvements in SPA cryo-EM and cryo-ET with subtomogram averaging analyses have recently provided the first 3D structures of complete filaments from wildtype Leptospira spp.…”