Streptomyces coelicolor is characterized by a complex
life cycle and serves as a model system for bacterial
development. After a feeding substrate mycelium has
been formed, this filamentous bacterium differentiates
by forming aerial hyphae that septate into spores. The
bld cascade regulates initiation of aerial growth,
whereas the whi genes control spore formation. Recent
findings indicate the existence of another regulatory
pathway that operates after aerial hyphae have started
to grow into the air, which we call the sky pathway. This
pathway controls the expression of the chaplin and
rodlin genes. These genes encode proteins that
assemble into a rodlet layer that provides surface
hydrophobicity to aerial hyphae and spores.