Fig. 5

Representation of Fit and Mcf toxin variants. (a) Segments of same color represent highly identical regions (>60 % identity) between the different variants. Strains representing the toxin variants are indicated in bold in Fig. 1b. C80 peptidase is only present in Mcf3. TcdA/TcdB indicates the pore-forming domain present in all variants, but most likely of different origin (Fit/Mcf1/Mcf2 vs. Mcf3). The BH3 domain present in FitD, Mcf1 and Mcf2 has been attributed a functional role in cell death induction [22]. (b) Phylogenetic relationship of the bacterial TcdA/TcdB pore-forming domain present in all Fit and Mcf protein variants. The TcdA/TcdB domain from Rhodobacteraceae was designated as outgroup. The tree is based on 312 amino acids after removal of segments by Gblocks [54] and inferred using PhyML 3.0 with the HKY85 substituion model and default settings [55]. Bootstrap values are based on 100 replicates and given for relevant nodes indicated by circles. The range of amino acid identity of the TcdA/TcdB domain compared to the FitD reference sequence of CHA0 is given next to the colored boxes delimiting the different Mcf variants