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[US2-03] Characterization of Treponema denticola mutants lacking three FlaB flagellar proteins
キーワード：Treponema denticola、Flagellar、FlaB
The oral spirochete Treponema denticola is considered to be responsible for the progression of human periodontal disease. The flagellar filament of T. denticola consists of three core proteins FlaB1, FlaB2, and FlaB3. They are with high amino acid sequence homology. In this study, we constructed gene-deletion mutants of all combinations of genes encoding the three proteins (flaB1, flaB2, and flaB3) and characterized the mutant strains. We used a derivative strain of ATCC 35405, which lacked a phage-derived region as a parent strain (10.1371/journal.pone.0270198). Compared to the original ATCC 35405, this strain exhibits enhanced growth, decreased motility, and higher efficiency in constructing gene-deletion mutants. Mutants with gene deletion were constructed by homologous recombination with antibiotic resistance gene cassettes. Western blot analysis showed that deleting the flaB genes abolished the expression of the corresponding proteins. FlaA, a flagellar sheath protein, was also detected in all mutants except ΔflaB123. The growth rate and the bacterial density at the plateau phase were decreased in ΔflaB123, and tended to decrease in ΔflaB12 and ΔflaB23. Cell body length was significantly longer in ΔflaB13 and ΔflaB123. Bacterial motility was decreased in ΔflaB12 and ΔflaB123, whereas increased in ΔflaB2 and ΔflaB13. Collectively, mutation of flaB genes causes differences in morphology, growth, and motility in T. denticola. These results suggest that there are functional differences in the three FlaB proteins. Conflict of Interest: The authors declare no conflict of interest associated with this manuscript.