Fine Structure of the Spore Sheath in Streptoverticillium Species

Actinomycetes bearing whorls and umbels of short spore chains at regular intervals on their long aerial hyphae and originally included in the genus Streptomyces were later reclassified as a separate genus Streptoverticillium (Baldacci, I 958, Baldacci, Farina & Locci, I 966). However, these two genera share a number of common morphological, developmental and physiological characteristics which have prevented several workers from accepting their separate generic status (e.g. Krasilnikov, I 970). The similarities have also appeared to discourage the further study of streptoverticillia and it has been assumed that other properties are shared. During an extensive scanning electron microscope study of the morphology of Streptoverticillium species (Locci & Petrolini Baldan, 1971) it was noticed that all showed twisted umbel hyphae which later became subdivided into the chains of arthrospores. No true spirals were observed and when viewed in silhouette by means of the transmission electron, microscope the individual spores have appeared smooth (Shirling & Gottlieb, 1968 a, b, 1969) and lack the conspicuous warts, spines and hairs (Kiister, 1955) or knobs (Lyons & Pridham, 1971) which ornament certain Streptomyces species. These surface structures develop from the spore sheath (Arai & Kuroda, 1962; Rancourt & Lechevalier, 1964) which also characteristically bears many short and randomly arranged elements termed fibres or rodlets (Vernon, 1955; Hopwood & Glauert, 1961 ; Dietz & Mathews, 1962; Wildermuth, 1970, 1972 a, b; Enquist & Bradley, 1971 ; Wildermuth, Wehrli & Horne, 1971 ; Williams, Bradshaw, Costerton & Forge, 1972). The fine structure of the Streptoverticillium spore sheath was examined to explain the twisted form of the umbel hyphae and the lack of appendages.