FIG 4.

Alternative Streptomyces growth modes. (A) Exploratory growth is triggered in response to glucose depletion (e.g., when cells are grown beside yeast). Explorer cells grow as nonbranching vegetative hyphae and expand rapidly across solid surfaces. (B) S-cells are extruded from hyphal tips following exposure to hyperosmotic stress or cell wall-targeting antibiotics. S-cells are vesicle-like structures that lack a cell wall and contain all cellular components to replicate. Both explorer and S-cells are transient cell types that can revert to the classic developmental program (Fig. 1).