Metabolism

 

Picture of T.pallidum invading host tissue

T. pallidum cannot be cultured in the lab because of its many metabolic requirements and susceptibility to desiccation and heat shock. T. pallidum is chemoheterotrophic and relies on obtaining many of its nutrients from its host. It lacks enzymes necessary to synthesize fatty acids, nucleotides, enzyme cofactors and most amino acids. It does have genes that encode all the enzymes required for glycolysis including hexokinase, but not for gluconeogenesis. T. pallidum also lacks genes for a phosphoenolpuruvate phosphotransferase system and obtains carbohydrates through ATP-binding cassette (ABC) transporters. It has 18 ABC transporters each specific for a certain sugar, amino acid, or cofactor. This organism relies on energy produced through the glycolytic pathway and does not have the machinery for the tricarboxylate cycle, or oxidative phosphorylation. As a result of not having these enzymes with heme cofactors and other proteins that require iron T. pallidum does not have the need for iron acquisition, which is generally a hallmark of the host-pathogen relationship.