Metabolism in Mycobacterium leprae, M. tuberculosis and other pathogenic mycobacteria

Pathogenic mycobacteria have complex lipoidal cell walls. Most of them secrete further lipids which appear as a layer around intracellular organisms. This lipoidal exterior may protect mycobacteria inside macrophages from attempts that those host cells make to kill them. Such protection could be especially important in M leprae which unusually lacks catalase, an important ‘self-defence’ enzyme. Intracellular mycobacteria must obtain key nutrients from the host. The role of mycobactin and exochelin in acquiring iron, the carbon and nitrogen sources—including metabolic intermediates—used, and control of biosynthetic pathways are discussed. M. tuberculosis is capable of synthesising all its macromolecules but M. leprae depends on the host for purines (precursors of nucleic acids), and maybe other intermediates Pathogenic mycobacteria grow slowly, and the possibilities that permeability of the envelope to nutrients, catabolic or anabolic (particularly DNA, RNA synthesis) reactions are limiting to growth are considered. Some characteristic activities may represent targets for antimycobacterial agents.