Transcription regulator TrtA modulates oxygen stress response in <i>Treponema denticola</i>

Periodontitis is caused by dysbiosis of the subgingival microbiome. <i>Treponema denticola</i> is an obligate anaerobe frequently detected in advanced periodontal lesions. However, the mechanism by which <i>T. denticola</i> evades oxygen stress remains unclear. TDE_0127 (<i>trtA</i>) encodes a potential transcriptional regulator in <i>T. denticola</i> and is upregulated in response to oxygen exposure. However, its exact function is unclear. This study aimed to investigate the involvement of TrtA in the oxygen stress response of <i>T. denticola. trtA</i> expression increased under oxygen exposure. RNA-seq analysis revealed that the expression levels of 38 genes, including that encoding internalin-related protein, were significantly upregulated under anaerobic conditions, and 153 genes, including those encoding peroxiredoxin and dentilisin, were significantly downregulated (|log₂(mutant/wild type)| >1.5, false discovery rate <0.05) in the <i>trtA</i>-deletion mutant. Under aerobic conditions, peroxiredoxin expression was lower and the viable cell proportion was significantly lower in the <i>trtA-</i>deletion mutant than in the wild-type strain (<i>P</i> < 0.001), suggesting that TrtA is involved in oxygen resistance via peroxiredoxin regulation. In contrast, internalin-related protein expression in the <i>trtA-</i>deletion mutant increased. Inactivation of internalin-related protein reduced the intracellular invasion of gingival keratinocytes, and quantitative reverse transcription PCR analysis showed that internalin-related protein expression in the wild-type strain decreased under oxygen exposure, suggesting that it is under TrtA regulation. Although dentilisin expression was downregulated in the <i>trtA</i>-deletion mutant, direct interaction was not elucidated. These results suggest that TrtA is involved in oxygen stress resistance and intracellular invasion in <i>T. denticola</i>.IMPORTANCE<i>Treponema denticola</i> is prevalent in advanced periodontal lesions and is involved in the pathogenesis and progression of periodontitis. During dysbiosis of the subgingival microbiome, <i>T. denticola</i> resists the effects of environmental oxygen and H₂O₂ released from commensal bacteria. In other periodontopathic bacteria, genes encoding master regulators of oxygen stress, such as OxyR, have been detected in the genome. However, an ortholog of such a regulator is yet to be detected in the genome of <i>T. denticola</i>. Herein, we show, for the first time, that TrtA is involved in the oxygen stress response of <i>T. denticola</i>. The expression of 153 genes was attenuated in the <i>trtA-</i>deletion mutant, indicating that TrtA influences a broad range of cellular processes. TrtA regulates the oxygen stress response in part through peroxiredoxin. In addition, internalin-related protein, which may participate in the host cell invasion by <i>T. denticola</i>, is under the control of TrtA.