Although conversion of rod-shaped or coccal bacterial cells into spheroplasts and protoplasts and the subsequent growth in the L-form state are well-known for many species of different genera (HIJMANS et al. 1969) there are only a few reports about L-forms in Actinomycetales (HORWITZ and CASIDA 1975, BOURGEOIS and BEAMAN 1974, 1976, BEAMAN et al. 1978 and no information about L-forms in Streptomyces strains.I n a previous paper (GUMPERT 1978) we mentioned the induction of L-form growth in Streptomyces hygroscopicus on agar media. I n the following report isolation, growth conditions, and some morphological data will be described.Induction of L-form growth: In contrast to gram-negative and most other grampositive bacteria in which L-forms are induced by penicillin or lysozyme treatment of normal rod-shaped or coccal cells, isolated protoplasts had to be used for L-form induction in 8. hygroscopicus. For obtaining the protoplasts, S. hygroscopicus was grown in a complex glucose-peptone medium supplemented with yeast extract (0.4%) and glycine (lye). After 16-20 hrs shaking at 28 "C mycelial aggregates were harvested by centrifugation and resuspended in a protoplasting medium according to OKANISHI et al. (1954; PM, Tab. 1). Protoplasts formed during a 30-60 min period were purified by ultrafiltration through a glas filter (SCHOTT Jena, pore diameter about 20 pin), centrifuged and inoculated onto an L-induction medium (LIM, Tab. 1). Typical L-colonies are formed during 7 days incubation a t 28 "C under aerobic conditions. Cultivation of L-forms: A subsequent permanent growth in the L-form state could be obtained by transferring L-form colonies onto fresh L-medium (LM, Tab. 1) supplemented with glycine and penicillin or only glycine (1%).L-form growth was also possible in liquid L-medium. Induction of L-form growth and subsequent cultivation are reproducible. Some isolates were cultivated for more than 20 transfers. Until now a stable L-form growing without penicillin and glycine could not be isolated either on plates or in liquid media. Both substances are known as inhibitors of murein biosynthesis, and if they are lowered to a certain concentration (less than I : / , glycine) regeneration to normal filamentously growing hyphal cells takes place.Morphology of L-form colonies: On agar media L-forms grow as characteristic friedegg colonies with a dark centre and a brighter periphery (Fig. 1). The centre consists of L-form cells growing into the agar. I n the peripherical zone there are intact and lysed cells ranging in size from 0.3 to 15 pm in diameter (Fig. 2). L-form cells grow in liquid media as small aggregates consisting of spherical cells often arranged in chains.

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