FIG. 6.

Pock formation, indicating the intramycelial plasmid spreading. (A) If spores of a donor strain carrying a self-transmissible plasmid are mixed with an excess of plasmid-free recipient spores, characteristic growth retardation zones (pocks) are formed, indicating the area where the recipient mycelium has acquired a plasmid. The size of the pocks depends on the action of the spd genes. (B) In S. lividans pock formation is also associated with the induction of the red-pigmented antibiotic actinorhodin. (C) A pIJ101-carrying donor was streaked on a lawn of a recipient expressing gfp from Aequorea victoria. Since the aerial mycelium and spores of S. lividans show red autofluorescence, only the pock regions, where morphological differentiation is retarded, light up green.