[Actinomycete formation of asporogenic secondary colonies and the properties of their isolated variants].

The frequency at which asporogenic secondary colonies were produced by actinomycetes was studied during their cultivation in media conventionally used for maintaining collections. 500 collection cultures and 200 freshly isolated cultures belonging mainly to the series Cinereus of the genus Streptomyces were screened. Plicate secondary colonies having 1--3 mm in diameter and lacking aerial mycelium and spores were found above the surface of the arterial mycelium very rarely in the studied actinomycetes: these were detected only in 19 cultures growing for 7--14 days. Stable asporogenic (devoid of aerial mycelium and spores) variants were isolated from the secondary colonies of five cultures. The properties of the asporogenic variants were compared with those of the sporulating parent cultures. The asporogenic variants were characterized by the absence of certain pigments, the assimilation of individual carbon sources, and a lower growth rate. Instead of LL-diaminopimelic acid (DAP) contained in the cell wall of the parent culture, meso-DAP was found in the cell wall of the asporogenic variant of Streptomyces galilaeus INA 5888.