The fine structure of Streptomyces coelicolor. II. The nuclear material

Ultrastructure of Exospore Formation in Streptomyces Revealed by Cryo-Electron Tomography

Many bacteria form spores in response to adverse environmental conditions. Several sporulation pathways have evolved independently and occur through distinctive mechanisms. Here, using cryo-electron tomography (cryo-ET), we examine all stages of growth and exospore formation in the model organism Streptomyces albus. Our data reveal the native ultrastructure of vegetative hyphae, including the likely structures of the polarisome and cytoskeletal filaments. In addition, we observed septal junctions in vegetative septa, predicted to be involved in protein and DNA translocation between neighboring cells. During sporulation, the cell envelope undergoes dramatic remodeling, including the formation of a spore wall and two protective proteinaceous layers. Mature spores reveal the presence of a continuous spore coat and an irregular rodlet sheet. Together, these results provide an unprecedented examination of the ultrastructure in Streptomyces and further our understanding of the structural complexity of exospore formation.

The fine structure of the nuclear material of a blue-green alga, Anabaena cylindrica Lemm

The chromatinic material of the blue-green alga Anabaena cylindrica has complex configurations in the central regions of the cells. The distribution of the chromatin within the cells varies in different filaments, probably in response to variations in the disposition of other cellular components. In electron micrographs of thin sections of organisms fixed by the method of Kellenberger, Ryter, and Séchaud (1958) the centroplasm contains fibrillar and possibly granular components which can be identified as the nuclear material by comparison with stained preparations viewed in the light microscope. The fibrils in the nuclear regions have diameters in the range of 5 to 7 mmicro and are embedded in a matrix of lower density. The nuclear regions are not greatly different from the cytoplasm in their electron density. Reducing the calcium content of the fixative results in coagulation of the fibrils to form coarser structures. The significance of the observations is discussed in relation to observations on the fine structure of other classes of algae and of bacteria.

Observations on the chromatinic bodies of Streptomyces coelicolor

Colonies of Streptomyces coelicolor growing on cellophane and impression preparations from sporing colonies were stained for chromatin by the methods of Feulgen, DeLamater (1951), and Piéchaud (1954). The chromatinic bodies of the substrate hyphae have a great variety of configurations. During the development of the spores, elongated chromatinic structures in the young aerial hyphae separate into a number of subunits and a single round chromatinic body is included in each spore.

Cytological aspects of antimicrobial antibiosis. I. Cytological changes associated with the exposure of Escherichia coli to colistin sulfate

Chapman, George B. (Cornell University Medical College, New York, N.Y.). Cytological aspects of antimicrobial antibiosis. I. Cytological changes associated with the exposure of Escherichia coli to colistin sulfate. J. Bacteriol. 84:169-179. 1962-Broth cultures of Escherichia coli were exposed to different concentrations of the antibiotic colistin sulfate for various lengths of time. Control (untreated) and treated cells were fixed, dehydrated, and embedded in methacrylate or Epon. Ultrathin sections were examined in an RCA EMU2-D electron microscope. Two conspicuous cytological changes were noted. First, the nuclear material disappeared from its normal sites and was no longer demonstrable. Second, the cytoplasm lost its granularity and became homogeneous. Cells which showed these changes were nonviable.

Observations with the electron microscope on the fine structure of the nuclei of two spherical bacteria

The nuclei of two spherical bacteria have been examined in electron micrographs of thin sections of specimens prepared by the method of Ryter and Kellenberger (1958). The nuclei appear to consist of the same fine fibers in a matrix of low density which have already been seen in many other bacteria prepared by the same procedure. They are worth a separate description because their constituent fibers are arranged in patterns of uncommon orderliness. In the nuclei of one of the two bacteria this is seen at all times, in the nuclei of the other one only at the beginning of the growth cycle. In some places the diameter of the nuclear fibers is close to that of the DNA molecule in the model of Watson and Crick (1953).

Fine structure of the photosynthetic bacterium Rhodomicrobium vannielii

The fine structure of the photosynthetic bacterium Rhodomicrobium vannielii was studied by the ultra thin sectioning technique. Cells were fixed in buffered osmium tetroxide and embedded in Epoxy resin. The feature most common to nearly all cells was an array of intracellular membranes situated in a concentric manner at the periphery of the cell. The membranes were mostly paired and quite often five pairs were seen aligned together. Calculations from densitometric tracings showed the average width of a "unit" membrane to be 65 A. Sections of material from disrupted cells after passage through a sucrose gradient revealed vesicular forms composed of membranes similar in width to those in the intact cell. Absorption spectra of both intact cells and isolated membranes were very similar in the bacteriochlorophyll regions. Septa and membranes were demonstrated in the filaments that join mature cells. No evidence for chromatophores was obtained although the methods used were adequate for their demonstration in Rhodospirillum rubrum.

The fine structure of Streptomyces violaceoruber (S. coelicolor). III. The walls of the mycelium and spores

A study of thin sections of hyphae of Streptomyces violaceoruber in the electron microscope showed that the structure of the walls and the mode of formation of cross-walls are similar to those of Gram-positive bacteria. A beaded structure was seen in some regions of the wall, and the significance of this observation is discussed in relation to previous studies of the fine structure of bacterial cell walls. Elements of the intracytoplasmic membrane system appear to be involved in the process of cross-wall formation. The walls of the hyphae of the aerial mycelium divide into two layers before the spores are formed, and only the inner component of the wall grows inwards to form the cross-walls and so delimit the spores. The outer component remains intact for a time and acts as a sheath around the developing spores. Finally the sheath breaks and the spores are liberated. This process is contrasted with the formation of endospores in eubacteria. When the spores germinate, the walls of the germ tubes are continuous with those of the spores.

Cytological aspects of antimicrobial antibiosis. I. Cytological changes associated with the exposure of Escherichia coli to colistin sulfate

Chapman, George B. (Cornell University Medical College, New York, N.Y.). Cytological aspects of antimicrobial antibiosis. I. Cytological changes associated with the exposure of Escherichia coli to colistin sulfate. J. Bacteriol. 84:169-179. 1962-Broth cultures of Escherichia coli were exposed to different concentrations of the antibiotic colistin sulfate for various lengths of time. Control (untreated) and treated cells were fixed, dehydrated, and embedded in methacrylate or Epon. Ultrathin sections were examined in an RCA EMU2-D electron microscope. Two conspicuous cytological changes were noted. First, the nuclear material disappeared from its normal sites and was no longer demonstrable. Second, the cytoplasm lost its granularity and became homogeneous. Cells which showed these changes were nonviable.

Influences of developmental genes on localized glycogen deposition in colonies of a mycelial prokaryote, Streptomyces coelicolor A3(2): a possible interface between metabolism and morphogenesis

Two spatially localized phases of glycogen accumulation were detected by electron microscopy after cytological staining of thin sections of Streptomyces coelicolor A3 (2) colonies. In phase I, glycogen granules were present in hyphae in the air—agar interface region of colonies that were undergoing aerial mycelium formation, though absent from aerial hyphae themselves. With one exception (a bldF mutant, which contained abundant glycogen), the absence of aerial mycelium caused by various developmental mutations ( bldA, bldB, bldC, bldD, bldG and bldH mutations) was associated with a virtual absence of detectable glycogen. Mutations that allow aerial hyphae to form but prevent or interfere with the septation needed for spore formation ( whiA,whiB, whiG, whiH and whil mutations) did not impair phase I deposition. In phase II, abundant glycogen granules were present in aerial hyphal tips during intermediate stages of sporulation, but disappeared as spores matured. Phase II glycogen accumulation was observed with bldA, bldC, bldD and bldG mutants grown with mannitol as carbon source — conditions that allowed normal aerial mycelium development and sporulation; but phase I deposition was still at a very low level in these colonies. Glycogen was also deposited in the coiling tips of aerial hyphae of whiA , whiB, whiH and whil mutants, and sporadic clusters of granules were present throughout whiG colonies. Significantly, glycogen was deposited in spore chains that developed ectopically in the normally sporeand glycogen-free substrate mycelium when multiple copies of whiG were present. Overall, the two phases of glycogen synthesis (and degradation) appear to be under separate developmental control rather than being mainly responsive to external growth conditions. Phase II glycogen levels were particularly high in a whiE mutant defective in spore pigment biosynthesis, and particularly low when hyper-pigmentation was induced by additional copies of the whiE genes. Spore pigment may therefore be a major sink for carbon stored as glycogen during sporulation. The possibility is discussed that, in addition to supplying carbon and energy at particular locations, glycogen synthesis and degradation may also play a part in morphogenesis by influencing turgor pressure.

TYROSINASE INHERITANCE IN STREPTOMYCES SCABIES. I. GENETIC RECOMBINATION

Gregory, Kenneth F. (Ontario Agricultural College, Guelph, Ontario, Canada), and Jay C. C. Huang. Tyrosinase inheritance in Streptomyces scabies. I. Genetic recombination. J. Bacteriol. 87:1281-1286. 1964.-Mutants derived from Streptomyces scabies strain A26 recombined with other derivatives of A26, but not with nine other strains of S. scabies nor with eight strains of other streptomycetes. Most of the spore progeny of heterogenomic mycelia formed from complementary diauxotrophic strains of S. scabies A26 were capable of forming tyrosinase (tye(+)), provided either of the parents was tye(+). About 99.8% of these spores carried the nutritional markers of either one or the other of the two parents. All recombinant classes between nutritional and streptomycin susceptibility markers were like-wise predominantly tye(+). We suggest that the tye(+) characteristic is carried in a small genetic unit, which is unlinked to most other genes and capable of replicating faster than the rest of the S. scabies genome.

FINE STRUCTURE OF LISTERIA MONOCYTOGENES

Edwards, Mercedes R. (New York State Department of Health, Albany) and Roy W. Stevens. Fine structure of Listeria monocytogenes. J. Bacteriol. 86:414-428. 1963.-Cells of Listeria monocytogenes, at different stages of growth, were fixed with osmium tetroxide and treated with uranyl acetate. The material was dehydrated in alcohol, embedded in prepolymerized methacrylate, and studied in thin sections. In most of the micrographs, the plasmalemma (or plasma membrane) showed a pattern of three dense lines, each ca. 25 A thick, alternating with two light zones, each ca. 30 A thick. The outer light zone was regularly bridged by strands of dense material, and the inner one was not. The dense line at the edge of the cytoplasm was not always discernible because of its similarity in density with the ground cytoplasm, although it could be easily demonstrated in lysed cells and in protoplasts. The latter were found to be limited by a pair of dense lines, each ca. 25 A thick, bounding a light core ca. 30 A thick. This structure corresponds to a "unit" membrane, but it represents only a part of the plasmalemma of the intact cell; it was therefore interpreted as being more complex than a single unit membrane. Intracytoplasmic membranes of various configurations were clearly shown to be extensions of the plasmalemma. They may branch repeatedly and anastomose to form a complicated honeycomb-like organelle or organelles of different appearances, sometimes lamellate. The lamellar bodies are envisioned as resulting from spiraled ingrowths. The various kinds of ingrowths of the plasmalemma were designated "plasmalemmosomes" to indicate their origin; however, some of these organelles in Listeria were similar to those described in different bacteria by other authors. Plasmalemmosomes have been found in both aerobically and anaerobically grown cells. Another outstanding feature in many micrographs was the nucleoid, which contains dense fibrils measuring 25 to 50 A in diameter. These fibrils frequently appeared to be coiled and were of the order of magnitude ascribed to deoxyribonucleic acid molecules.

An unusual symbiont from the gut of surgeonfishes may be the largest known prokaryote

Symbionts first reported from the gut of a Red Sea surgeonfish, Acanthurus nigrofuscus (family Acanthuridae), were subsequently described as Epulopiscium fishelsoni. The taxonomic position of this very large (up to 576 microns in length) microorganism has previously been designated in the literature as either uncertain or eukaryotic. We suggest that similar symbionts from Great Barrier Reef surgeonfish may be prokaryotes, which together with E. fishelsoni from the Red Sea may represent the largest known forms of this cell type. Features identifying the symbionts as prokaryotes include the presence of bacterial-type flagella and a bacterial nucleoid and the absence of a nucleus or any other membrane-bound organelle.

Growth mechanisms and growth kinetics of filamentous microorganisms

Filamentous microorganisms are of major biotechnological importance, being responsible for production of the majority of secondary metabolites, particularly antibiotics. Two main groups are involved, filamentous fungi and filamentous actinomycetes, particularly the streptomycetes. In terms of cellular growth mechanisms, these groups differ greatly. Eukaryotic fungi possess subcellular organelles and cytoskeletal structures directing growth while prokaryotic streptomycetes have no such cellular organization. Despite these fundamental differences, both groups exhibit similar morphologies, growth patterns, growth forms, and hyphal and mycelial growth kinetics on solid media and in liquid culture both grow as dispersed mycelia and pellets. The article therefore discusses the relationship between cellular growth mechanisms and vegetative growth in both filamentous fungi and actinomycetes, the conceptual and theoretical models applicable to both groups, and the significance of such models in industrial fermentation processes.

Mesosomes: membranous bacterial organelles

Images

Corynebacterium diphtheriae and its relatives

Images

Composition and ultrastructure of Streptomyces venezuelae

Streptomyces venezuelae is a filamentous bacterium with branching vegetative hyphae embedded in the substrate and aerial hyphae bearing spores. The exterior of the spore is inlaid with myriads of tiny rods which can be removed with xylene. The spore wall is approximately 30 nanometers thick. Occasionally, it can be seen that the plasma membrane and the membranous bodies within a spore are connected. The spore's germ plasm is not separated from the cytoplasm by a nuclear envelope. The cell walls of the vegetative hyphae, which are about 15 nanometers thick, are structurally and chemically similar to those of gram-positive bacteria. The numerous internal membranous bodies, some of which arise from the plasma membrane of the vegetative hypha, may be vesicular, whirled, or convoluted. Membranous bodies are usually prominent at the hyphal apices and are associated with septum formation. The germ plasm is an elongate, contorted, centrally placed area of lower electron density than the hyphal cytoplasm. The spores differ from the vegetative hyphae, not only in fine structure, but also in the arginine and leucine contents of their total cellular proteins.

Formation of intracytoplasmic membrane system of mycobacteria related to cell division

Imaeda, Tamotsu (Instituto Venezolano de Investigaciones Científicas, Caracas, Venezuela) and Mitua Ogura. Formation of intracytoplasmic membrane system of mycobacteria related to cell division. J. Bacteriol. 85:150-163. 1963.-Mycobacterium leprae, M. lepraemurium, and a Mycobacterium sp. were observed with an electron microscope. In these bacilli, the three-dimensional structure of the intracytoplasmic membrane system consists of tubular infoldings of the invaginated plasma membrane. The moderately dense substance, presumably representing the cell-wall precursor, is found in the membranous system, especially in the rapid growth phase of mycobacteria. This system always shows an intimate relationship with cell division. A low-density zone, probably corresponding to the low-density substance which coats the cell wall, appears in the connecting regions of the system and in the longitudinal portion of the cell wall. These zones extend centripetally, and the separation of the cell wall occurs after the two zones meet. Based on these results, we hypothesize that the intracytoplasmic membrane system may produce cell-wall material during cell division of mycobacteria.