Alteration of interaction with virulent bacteriophage Ta1 during differentiation of Thermoactinomyces vulgaris.

During its life cycle Thermoactinomyces vulgaris 1227 and 1261 substrate mycelium showed three modes of interaction with the virulent phage Ta1, each expressed at a distinct morphological stage. Primary mycelium arising from spores 50 min after start of germination was the only stage which propagated phages upon infection. However, infection of growing secondary mycelium or of late sporulation stages resulted in a loss of phage. The lack of phage production upon infection of growing secondary mycelium was not related to sporogenesis, since it appeared already 3.5 hours before the beginning of sporulation. If phages were added to the secondary mycelium at the beginning of spore formation, the phage genome became integrated in the developing spores in a heat-stable state. Allowing outgrowth of these prophage-carrier spores, phages were produced similarly as in germ tubes arising from normal spores infected at the time of inoculation. The growing secondary substrate mycelium was characterized by competence for the uptake of exogenous DNA. Since at the stage of competence phages were neither produced nor was phage DNA trapped, the earlier reported lack of transfection in undisturbed differentiating T. vulgaris is now understandable.