 Treponema pallidum subspecies pallidum is a spiral @-@ shaped , Gram @-@ negative , highly mobile bacterium . Three other human diseases are caused by related Treponema pallidum , including yaws ( subspecies pertenue ) , pinta ( subspecies carateum ) and bejel ( subspecies endemicum ) . Unlike subtype pallidum , they do not cause neurological disease . Humans are the only known natural reservoir for subspecies pallidum . It is unable to survive without a host for more than a few days . This is due to its small genome ( 1 @.@ 14 MDa ) failing to encode the metabolic pathways necessary to make most of its macronutrients . It has a slow doubling time of greater than 30 hours . 
