Longitudinal sections of Streptomyces antibioticus ATCC11891 surface cultures obtained using a diluted inoculum (6 × 103 spores per plate). The developmental phases (A'-H') and culture times are indicated. Samples were stained with SYTO 9 and propidium iodide. Arrow in picture A' indicates a group of hyphae in transition from presenting uniform green fluorescence to a variegated appearance, in which live (green) and dead (red) segments alternate in the same hypha. See text for details.