FIG. 3.

Rescue of developmentally blocked mutants by buffer or extracellular complementation. (A) pH control rescues morphological differentiation of the citA and bldJ (bld261) mutants. BZ2 (citA; plates 1 and 2) and HU61 (bldJ; plates 3 and 4) were grown at 30°C either on R2YE plates (plates 2 and 4) or R2YE supplemented with 100 mM TES (plates 1 and 3). (B) Aerial hypha formation of BZ2 (citA; right half of plate) was induced when the strain was grown next to the acidogenic bldA mutant. The pH of both mutant cultures, recorded on pH papers, dropped to less than 5.0 (yellow pH paper) and remained acidic at the edge of the plate, where differentiation was blocked. In closer proximity, interactions between the strains first allowed differentiation of the citA mutant associated with neutralization of the medium (pH 6.0, red pH paper). Several days later, the bldA mutant produced few aerial mycelia in response to differentiating citA mutant mycelium. (C) Developmentally blocked mutants citA (BZ2; center), bldA (A), bldD (D), bldC (C), and bldB (B). All mutants except bldC induced aerial mycelium formation in the citA mutant. (D) Developmentally blocked mutants citA (BZ2; center), bldG (G), bldK (K), bldJ (261), and bld5 (5, a previously undescribed S. coelicolor bald mutant isolated by K. Nguyen). All mutants except bldJ induced aerial mycelium formation in the citA mutant. In contrast, bldJ was induced to form aerial mycelium by the citA mutant.