Regulation of Substrate Uptake in Nocardia erythropolis

The regulation of uptake of glucose (GLU), glycerol (GLY), mannitol (MTL), and succinate (SUC) has been examined in Nocardia erythropolis 305. The apparent K_m values of the uptake activities of cells subcultured in a medium with the corresponding substrate as the sole carbon source were 205, 48, 8.7, and 36 μM for GLU, GLY, MTL, and SUC, respectively. GLU and GLY uptake activities were constitutive, although there was evidence for an additional inducible component in GLY uptake. Moreover, MTL and SUC uptake activities were inducible. MTL uptake activity was markedly induced by cultivation in MTL medium and partially induced by growth in GLU medium, whereas SUC uptake was induced only by cultivation in SUC medium. SUC added to MTL medium partially repressed the formation of, or inhibited the activity of, MTL uptake. When not induced, uptake of MTL and SUC was proportional to the substrate concentration. The induced uptake of MTL and SUC and the constitutive uptake of GLU were energy dependent and carrier mediated. Uptake of GLY, constitutively or when induced, was also carrier mediated.