**4.5 Cell wall, membrane, and transport**

The cell wall and inner plasma membrane are components of the complex cell envelope of mycobacteria. The inner plasma membrane contains a lot of transport systems. Some genes of these systems were observed to be upregulated, among them the *irtA/B* genes encoding carboxymycobactin transporters (Li et al., 2010; Schnappinger et al., 2003; Tailleux et al., 2008), the *sugI*, *Rv2040c* and *Rv2041c* genes of carbohydrate transporters (Azhikina et al., 2010; Schnappinger et al., 2003; Tailleux et al., 2008), and the *narK2* gene of the nitrate transporter protein (Azhikina et al., 2010; Garton et al., 2008; Tailleux et al., 2008; Talaat et al., 2007).

Enhanced expression of the genes of siderophore-synthesis enzymes, mycobactin and carboxymycobactin (*mbtA-J*, *mbtL-N*), could be explained by limited access to iron (Azhikina et al., 2010; Schnappinger et al., 2003; Tailleux et al., 2008).
