Fig 2.

Titration of tnaA reporter gene expression using the dual control inducible system in F. nucleatum (A). Genetic map of pBCG07 for gene expression studies. The expression of tnaA, a gene for tryptophanase that converts tryptophan to indole, is controlled by P _xylAB and riboswitch at both the transcriptional and translation levels. (B) TnaA-inducible expression level in response to the inducer(s) concentration. The TnaA activity can be monitored by indole production. The indole production was demonstrated by adding Kovac’s reagent, which acts with the indole giving a red color in fusobacterial cultures. F. nucleatum ∆tnaA strain carrying pBCG07 was cultivated in a TSPC medium in the presence of a different concentration of inducers for 12 hours of growth. (C) Indole production due to TnaA presence was qualified by indole assay. The measurement of indole production was repeated three times, and the mean values of one representative experiment performed in triplicate are reported and indicated.