Changes in the surface layer (sheath) of the cell wall of streptomycetes during sporulation

Fine structural changes of the sheath, occurring during spore formation in strains Streptomyces finlayi ATCC 23 340 and Streptomyces coeruleorubidus FBUA 328 were investigated by means of electron microscopy of air-dried whole mounts and thin sections. The results suggest that in the strains the process of sporulation is not strictly synchronized spatially with the molecular arrangements and re-arrangements (formation of hairy or spiny surface ornaments) occurring outside the wall of the sporulation hyphae, in the sheath. On the contrary, the intensity of transformation induction in the sheath may show a gradually decreasing tendency from the tip of the sporulating hypha towards its sterile basal part, resulting in the formation of both ornamented and smooth spores in the same chain. This suggests that the morphogenetic changes occurring in the sheath during spore formation are probably controlled by a "functional centre", located near the tip of the sporulating hypha, and this centre is perhaps indentical with the cell unit at the tip.