TetR Is a Positive Regulator of the Tetanus Toxin Gene in Clostridium tetani and Is Homologous to BotR

ABSTRACT The TetR gene immediately upstream from the tetanus toxin (TeTx) gene was characterized. It encodes a 21,562-Da protein which is related (50 to 65% identity) to the equivalent genes (botR) inClostridium botulinum. TetR has the feature of a DNA binding protein with a basic pI (9.53). It contains a helix-turn-helix motif and shows 29% identity with other putative regulatory genes inClostridium, i.e., uviA from C. perfringens and txeR from C. difficile. We report for the first time the transformation of C. tetani by electroporation, which permitted us to investigate the function of tetR. Overexpression of tetR inC. tetani induced an increase in TeTx production and in the level of the corresponding mRNA. This indicates that TetR is a transcriptional activator of the TeTx gene. Overexpression ofbotR/A (60% identity with TetR at the amino acid level) inC. tetani induced an increase in TeTx production comparable to that for overexpression of tetR. However,botR/C (50% identity with TetR at the amino acid level) was less efficient. This supports that TetR positively regulates the TeTx gene in C. tetani and that a conserved mechanism of regulation of the neurotoxin genes is involved in C. tetaniand C. botulinum.