Ultrastructure of Nocardia cell growth and development on defined and complex agar media.

The cell growth of Nocardia strain 721-A on Brain Heart Infusion Agar (BHIA), nutrient agar, and chemically defined agar media was studied by light and electron microscopy. Light microscopy revealed a change in cell morphology induced by growth on BHIA. Electron microscopy demonstrated a concurrent change in intracellular complexity. On BHIA, the cells became bulbous and developed irregularly branched filaments which fragmented by multiple and random septation. These fragments appeared to undergo a secondary stage of development similar to that described for Arthrobacter. Cells grown on defined or nutrient agar did not become bulbous and lacked the unusual complexity found in cells grown on BHIA. Intracytoplasmic membranes were altered by the nutritional state of the cell and changed during cell development.