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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.

When Streptomyces roseoflavus var. roseofungini is grown as a submerged culture in a chemically defined medium with stirring, it yields a number of variants in which the capacity to form the aerial mycelium is disturbed. Inoculations of the submerged mycelium of different age into a solid medium give rise to both "tomentose" variants (TV) with the aerial mycelium and "naked" variants (NV) lacking the aerial mycelium. The latter variants comprise Nocardia-like variants (NLV) with the fragmenting mycelium. The following change in the variants occurs in the inoculations of the submerged mycelium in the course of the cultural growth: TV leads to NV leads to NLV or (more rarely) TV leads to NLV. The dynamics of accumulation of the variants depends, to a considerable extent, on the source of carbon in the medium: NLV first appear on the medium containing fructose; NV are detected first on the medium with glucose; NV are rarely found on the medium with mannitol. In aged cultures, the number of NLV can reach 80--90%, the content of TV is 20--10%, and NV are absent. The above results suggest that the formation of NLV from S. roseoflavus var. roseofungini is the result of stepwise selection.

IR spectra of the whole cells of oligosporous actinomycetes were studied. These spectra can be used as an additional criterion during identification of actinomycetes at the generic level, and confirm the heterogeneity of the Micropolyspora genus so that some of its species may be classed as an individual genus (Kalakoutskii et al., 1968; Agre, Dorokhova, 1972).

Morphological, cultural and physiological properties of two strains of soil thermophilic actinomycetes were studied. These strains were compared to the actinomycetes of related genera and were found to be close to Micropolyspora and Actinomadura. However, they differed from both genera by the structure of the sporiferous apparatus, from Micropolyspora by the type of the cell wall, and from Actinomadura by the fatty acid composition of lipids of the mycelium. A new genus of actinomycetes, Excellospora Agre a. Guzeva gen. nov., is suggested on the basis of this study. Two species belonging to the genus Micropolyspora are proposed to assign to the new genus as Excellospora viridinigra and Excellospora rubrobrunea. Since these strains differ from the aforementioned species by the traits used for differentiation of the species of actinomycetes, they are described as a new species of the new genus Excellospora Agre a. Guzeva gen. nov. sp. nov.

Adifferentiated Nocardia-like variants (Nv) of Streptomyces roseoflavus var. roseofungini, similar in their cultural characteristics with the variant 1-68 described elsewhere (Nikitina, 1968; Kalakoutskii a. Nikitina, 1976), can be obtained not only in the course of growth of the parent culture on a solid medium containing fructose in the form of secondary colonies, but also during submerged cultivation with stirring. Interruptions in aeration do not affect accumulation of the cells of such variants in the medium. A direct correlation has been established between the amount of biomass and the number of Nv colonies when submerged mycelium is inoculated into a solid medium.

Passage of cultures of Thermoactinomyces vulgaris on a peptone-maize medium causes their degeneration which is manifested in an impaired formation of the sporulating aerial mycelium, and in an increase of the amount of non-germinating spores in populations. The process of degeneration depends on the following conditions: the location of the inoculated material (spores) on the surface of a solid growth medium, which is determined by the technique of inoculation; the state of the spores (degeneration is accelerated if the spores were not activated with low temperatures); the quality of the growth medium.

Studies of the morphology of Actinomadura spp. have shown that the genus comprises several morphological types of actinomycetes which differ by the presence and structure of the sporophores on the aerial and substrate mycelium. The actinomycetes differ also by the fatty acid composition of lipids in the mycelium, and can be subdivided into three groups: (1) fatty acids with a straight chain prevail; (2) fatty acids with branched chains of the iso- and anteiso structure predominate; and (3) fatty acids with straight and branched chains are contained in almost equal amounts. Therefore the genus separated on the basis of differences in the composition of the cell wall was heterogeneous according to the properties used in the taxonomy of the actinomycetes at the level of genus. These data prove that morphological properties have to be taken into account in the taxonomy of the actinomycetes.

The structure of spore surfaces was studied by electron microscopy in five species of actinomycetes, and two new types of elementary surface structures were discovered. The surface of spores in Streptomyces regensis consists of long flexible, closely interwoven, band-like structures 25 A wide. Ring-like structures 140--150 A in diameter can be observed on spores of Actinomadura verrucosospora; their clusters resemble grapes and the spore silhouette looks like a cone. Rod-like structures of spores in Streptomyces cavourensis and Str. streptomycini which form an ornament resembling the surface of a basket and tubular strucutres in Str. acrimycini of which hair-shaped spore protrusions are made are similar to the elementary structures of spore surfaces in other actinomycetes.

A new species of the Actinomadura genus, A. fastidiosa sp. nov., is described. The ultrastructure of the vegetative mycelium and spores of this organism was studied. The vegetative cells have a multilayered cell wall, often consisting of five layers with different thickness and electron density. The spores are similar to the vegetative cells by their inner structure but have a thicker wall.

The formation of spores was studied with a morphologic type of the Actinomadura genus, Acd. verrucosospora (Nonomura a. Ohara, 1971. Spore formation begins with the division of a hypha by cross-partitions which, as a rule, appear as monolayered on cross-sections, thus differing from sporulation septae found in other actinomycetes. The structure and shape of septae change in the course of spore formation: first, they consist of one layer and have the same thickness as the cell wall; later, they consist of several layers and their thickness is uneven (the shape of dumbbels). In the course of spore maturation, thick regions of the septae are destroyed. Mature spores are characterized by the presence of vacuoles, the thichened cell wall and outer sheath; the latter bears rounded structures arranged in conglomerates which resemble grapes. The process of sporogenesis and the structure of spores in Actinomadura verrucosospora differ from those in other species of the Actinomadura genus (Williams et al., 1974; Soina et al., 1975); therefore, this genus of actinomycetes is heterogenous.

It was shown that adifferentiated nocardioform variants (NV) of Streptomyces roseoflavus var. roseofungini 1128 may appear in mycelial cell suspensions of submerged actinomycete cultures in water, phosphate buffer, and water with fructose (1%) or glucose (1%), as well as in mycelia of old (10-30 days) cultures on different carbon sources. When sugars, alcohols, or amino acids were added to a medium with fructose, NV formation was inhibited, but not completely suppressed. Fructose was shown to be the most potent factor in the appearance of NV.

The fine structure of a fragmenting and sporulating mycelium of cultures of actinomycetes possessing biochemical properties characteristic of the genus Nocardia--a cell wall of type IV and lipid LCN a--was studied. It was found that fragmenting hyphae are similar in structure to the vegetative hyphae of known actinomycetes. Sporulation takes place through the simultaneous division of a sporulating hypha by numerous septa. Spores differ from vegetative cells in the presence of a thickened electron-dense cell wall, dense internal contents, and the presence of vacuoles.

The composition of cell walls was comparatively studied in Streptomyces roseoflavus var. roseofungini 1128 and in its variant 1-68. In the logarithmic phase of growth, the content of teichoic acid in the cell wall of the parent culture was four times as high as in the cell wall of the variant. The cell walls of the parent culture contained 5 to 7 times more O-lysyl residues not only due to a higher content of teichoic acid in the walls but also owing to a lower content of lysyl groups in the teichoic acid of the variant. An additional polysaccharide comprising galactose and glucosamine was found in the cell wall of the variant but not in the parent strain. The peptidoglycan of the both cultures had a structure typical of Streptomyces spp.; its content in the cell walls of the two cultures was identical (ca. 50% of the dry cell wall biomass weight). The results are discussed in connection with the peculiarities of the variant hyphal septation.

A synthetic medium was used to obtain the dormant spores of Thermoactinomyces vulgaris. The fraction of the dormant spores depended on the amino acid composition of the growth medium. The rate of growth and development of the organism on the synthetic medium is lower as compared to the routinely employed complex medium.

Endospores of Streptomyces streptomycini B-16 are considerably more thermostable (by 40degreesC) than it was generally accepted. The bulk of populations of the spores (up to 55%) can be subjected to 100degreesC during 10 min but does not germinate under usual conditions as a result of heat damage which may be repaired at a relative humidity of 100% or in water suspensions at temperatures optimal for growth of the actinomycete. The rate of reparation increase upon washing of the heated spores with stirring, centrifuging and especially after treating the spores with ultrasound. The treatment is supposed to eliminate from the spores growth inhibitors which were formed as a result of heat damage. Characteristics of the process are discussed, which make it different from other reparation systems described elsewhere, in particular its endogenous character.

The structure of teichoic acids was studied in the cell walls of Streptomyces roseoflavus var. roseofungini 1128 and its Nocardia-like variant 1-68 differing from the parent strain in the absence of a spore-forming aerial mycelium as well as by the fragmentation of hyphae in the substrate mycelium. The teichoic acids of the both cultures consist of a 1,3-poly(glycerophosphate) chain containing 11-13 glycerolphosphate residues which have glucosamynl units and lysine groups bound through an ester bond. These teichoic acids contain no O-acetyl groups, in contrast to the glyceroteichoic acids of actinomycetes studied earlier. The teichoic acid from the cell wall of the variant has less lysine and glucosamine then the parent strain. The content of teichoic acid in the cell wall of the parent culture is 4.5 times greater than in the wall of the variant.

Changes in the fine structure of the hyphae were studied in the course of spore formation by Micropolyspora fascifera. Sporulating hyphae differ from vegetative hyphae by a less dense cytoplasm, a large zone of the nucleoid with distinctly fibrillar structure, and a thin layerless cell wall. Spore formation is accompanied with autolysis of the vegetative hyphae, which consists in vacuolization of the hyphae and appearance of a large number of tubular membrane structures within them. Spores are formed, like in Actinomyces spp., by simultaneous division of the hyphae with septa; the structure of sporulating septa is similar to that of the fragmenting mycelium in Nocardia; the structure of mature spores is similar to that in some Actinomyces spp. Therefore, M. fascifera differs from other Micropolyspora spp. not only by the chemical composition of the cells (the presence of nocardiomicolic acids) but also by their structure. Taxonomic position of the species is discussed.