Mutagenesis of Treponema pallidum subsp. pallidum strain Madras with DAL-1 sequences

Treponema pallidum subsp. pallidum, the causative agent of syphilis, is considered a monomorphic bacterium, however, growth differences have been suggested between individual strains, such as DAL-1 and Madras which differ by only 43 genetic variants. Coding regions leading to amino acid changes present in the faster growing DAL-1 strain were used for in vitro mutagenesis of the Madras strain. Two recombinants carrying DAL-1-like alleles in TP0233 (G13D) and TP0720 (S123N) were obtained; both grew faster than the parental Madras strain and became fixed in the in vitro cultures. This study demonstrates that growth rates of T. pallidum strains are genetically determined.