Electron microscopy of Rhodotorula glutinis

FINE STRUCTURE OF MYCOTA : 4. The Occurrence of the Golgi Dictyosome in the Fungus Neobulgaria pura (Fr.) Petrak

Though the dictyosome of the Golgi apparatus appears to be generally distributed in plant and animal cells, it is here described for the first time in the fungi. The present report illustrates, in electron micrographs of thin sections, the characteristic structure of the Golgi dictyosome in a special cell type of a supporting pseudo-tissue (the inner ectal excipulum) of a highly evolved Ascomycete, Neobulgaria pura (Fr.) Petrak, a monotypic discomycete. This organelle may secrete the gelatinous matrix filling the cup formed by the inner ectal excipulum. All the other cells in this species appear more typical of fungal cells; i.e., they have no dictyosome and, unlike the cup-forming cells, they show characteristic continuities of the plasma membrane with the perinuclear cisternae. The dictyosome, in those cells in which it appears in this fungus, is formed by a series of vesiculations of the outer component of the nuclear envelope that align to form a stack of sacs. The sacs near the nucleus are flattened (by what appears to be an intermembrane cement) while those near the plasma membrane are more distended. These observations suggest three possibilities: first, fungi may be more closely related to other eukaryotic cells than previously suspected from electron microscopic studies; second, the outer nuclear membrane may have been the primitive precursor of the dictyosome; and third, the inverse relationship of the occurrence of the nuclear membrane plasma membrane continuities and the dictyosome suggests that the latter may have evolved as a means of removing from the cell the products of reactions occurring on a discontinuous membrane system.

CYTOLOGY OF CANDIDA ALBICANS AS INFLUENCED BY DRUGS ACTING ON THE CYTOPLASMIC MEMBRANE

Gale, Glen R. (Veterans Administration Hospital, Durham, N.C.) Cytology of Candida albicans as influenced by drugs acting on the cytoplasmic membrane. J. Bacteriol. 86:151-157. 1963.-An electron microscopic comparison was made of the cytological responses of Candida albicans to benzalkonium chloride, amphotericin B, and filipin, all of which are thought to exert their primary pharmacological actions on the cytoplasmic membrane of susceptible microorganisms. After 5 to 15 min of exposure to benzalkonium chloride, most of the cytoplasm became less dense, and intact nuclei, mitochondria, or intracytoplasmic membranes were not observed. The remaining dense cytoplasm contained numerous small holes. The polyene antifungal agents, amphotericin B and filipin, caused a reduction in cytoplasmic density, but had no observable effect on nuclei or mitochondria. The intervals before onset of changes induced by the polyene agents correlated with the known time-dependent binding of these drugs by cells, and the decreased electron scattering induced by all three agents was compatible with their known abilities to cause a loss of integrity of the cytoplasmic membrane with resultant leakage of cytoplasmic components. No consistent morphological effect of any of these drugs on the cytoplasmic membrane could be shown.

ELECTRON MICROSCOPY OF CELL FUSION IN CONJUGATING HANSENULA WINGEI

Conti, S. F. (Dartmouth Medical School, Hanover, N.H.), and T. D. Brock. Electron microscopy of cell fusion in conjugating Hansenula wingei. J. Bacteriol. 90:524-533. 1965.-The heterothallic yeast Hansenula wingei is a favorable organism for the study of the process of cell fusion, since strong agglutination of cells of the two mating types ensures a high percentage of cell fusions. The initial agglutination reaction results in cell-wall deformation, so that the walls in the region of contact are tightly appressed over an extensive area. The fusion process is initiated when the walls of two cells elongate, and this elongation seems to be restricted to the region where the cells touch. Occasionally, one cell is seen to push in the wall of the other, but in many cases both cells elongate equally, as would be expected in an isogamous organism. The precise disposition of the elongating wall probably reflects the manner in which the cells initially become associated in the agglutinated cell clump. Soon after wall elongation begins, cell-wall fusion occurs along the margin of contact. Only after fusion is complete is the wall separating the two cells dissolved away. If wall dissolution begins at one edge of the conjugation tube, a flap is formed in which can be seen the remnants of the fused walls. Alternatively, dissolution can begin at the center of the conjugation tube, proceeding towards the outside. Conjugating cells are uninucleate, and the nuclei are large and frequently lobed or elongated. After the conjugation tube is formed, the nuclei migrate towards the center, and fusion occurs only over a small region where the nuclear membranes come in contact. After nuclear fusion, the first diploid bud forms from the conjugation tube and at right angles to the tube axis. The diploid nucleus then migrates into this bud. Frequently, in the later stages of conjugation, a large vacuole develops in each of the original cells. All of the above events will occur in a medium devoid of a nitrogen source and in which vegetative budding will not occur.

Apical vesicles in growing bud cells of heterobasidiomycetous yeasts

Clusters of cytoplasmic vesicles resembling those in growing hyphal apices of mycelial fungi are found near the tips of buds in three heterobasidiomycetous yeasts, Rhodotorula glutinis, Candida scottii, and Sporobolomyces salmonicolor.

Surface structure of yeast protoplasts

The fine structure of the yeast cell wall during protoplast formation was studied by means of phase-contrast microscopy and the freeze-etching technique. The freeze-etching results indicated that at least in some cases the entire wall substance was not removed from the surface of the protoplasts. After a treatment of 30 min to 3 hr with 2% snail enzymes, an innermost thin wall layer as well as remnants of the fibrillar middle layer sometimes could be demonstrated.

Membranes of Saccharomyces cerevisiae

A crude small particle pellet, obtained from postmitochondrial supernatant fractions of Saccharomyces cerevisiae, contains about half the ergosterol and phospholipid of crude cell homogenates. Most of the phospholipid of this pellet is in a "heavy" fraction which, with the aid of electron microscopy, shows membranous elements in addition to discrete particles. The "heavy" fraction, upon treatment with deoxycholate, can be freed of membranes, or, with ribonuclease treatment, ribosomes can be removed, leaving relatively clean membranes. The "heavy" fraction resembles the microsomes of animal cells, but contains considerably less lipids, including phospholipids, thus suggesting a less well-developed intracellular membrane system.

MITOCHONDRIA FROM LIPOMYCES LIPOFER

Protoplasts of Lipomyces lipofer were ruptured by decompression in a French pressure cell. A particulate fraction sedimenting at 17,000 × g in saline or sucrose media contained the bulk of the substrate-dependent oxidative activity and was capable of phosphorylation. Particle fractions isolated in sucrose required supplementation with ATP and Mg2+while fractions from saline isolations required, in addition, NAD and cytochrome c. NADP and thiamine pyrophosphate had small or negligible effects in the presence of the other cofactors. Oxidative phosphorylation occurred most efficiently in particles isolated in sucrose, but in no case did the P/O ratio exceed 1.6. Electron microscopic examination of the sucrose-isolated fraction showed it to be a relatively homogeneous preparation of mitochondria which appear more "native" after incubation with substrate than immediately after isolation.

PREPARATION AND PROPERTIES OF PROTOPLASTS FROM LIPOMYCES LIPOFER

Lipomyces lipofer was grown aerobically in chemically defined liquid media containing glucose or citrate as a carbon source. Protoplasts were prepared by digestion of young cells with the intestinal secretions from Helix pomatia in the presence of 10% (w/v) mannitol. Differences in substrate utilization between citrate- and glucose-grown cells were noted and compared with the substrate utilization of the corresponding protoplasts. Examination of protoplasts derived from glucose- and citrate-grown cells showed that the citrate-grown organisms yielded morphologically and metabolically more stable protoplasts. The effects of hypotonic conditions on the metabolic activity of protoplasts as well as the consequences of supplementation of these protoplasts with cofactors have been described.

FINE STRUCTURE OF WHEAT STEM RUST UREDOSPORES

The fine structure of uredospores and germ tubes of Puccinia graminis f. sp. trilici is described from electron micrographs of cells fixed in KMnO4. In terms of their principal cytoplasmic structures (nuclei, mitochondria, endoplasmic reticulum, and protoplasmic and vacuolar membranes) these cells bear a general resemblance to other fungi and higher plants but differences between resting cells and germ tubes were noted in the size of oil bodies and the structure and extent of the endoplasmic reticulum.

EFFECTS OF SODIUM CAPRYLATE ON CANDIDA ALBICANS I

Adams , J. N. (University of Georgia, Athens), Barbara G. Painter, and W. J. Payne . Effects of sodium caprylate on Candida albicans . I. Influence of concentration on ultrastructure. J. Bacteriol. 86: 548–557. 1963.—Morphological effects of exposure to various concentrations of sodium caprylate were studied in living cells and ultrathin sections of Candida albicans . Budding was inhibited when cells were cultured in 0.0025 m sodium caprylate. Cells relieved from treatment at this concentration initiated reproductive processes at a much-stimulated rate. Momentary or 30-min exposures to 0.1 m caprylate affected cells in much the same manner as those treated at the lower concentration. Alteration of ultrastructure was brought about by treating with 0.0025 and 0.005 m concentrations prior to embedding and sectioning. Condensation of vacuolar material, change in size and number of mitochondria, loss of mitochondrial cristae, and increased electron density of the cytoplasm were observed. Cellular integrity was progressively lost as a result of treatment at levels up to 0.1 m . The highly electron-dense cytoplasm of cells cultured in media containing 0.025 m or higher inhibitor appeared to break into irregular masses, but the nucleus and vacuole sometimes could be identified. Cells treated at the 0.1 m level contained a condensed mass of opaque and unidentifiable cytoplasmic constituents within the skeletal cell wall. Cytological observations were correlated with physiological studies.

FINE STRUCTURE OF MICROSCLEROTIA OF VERTICILLIUM ALBO-ATRUM REINKE & BERTH

The fine structure of microsclerotia of Verticillium albo-atrum Reinke & Berth. is described. Fixing and embedding procedures are given. Microsclerotial units are composed of thin- and thick-walled cells in close association with each other. The larger thick-walled cells contain different cytoplasmic inclusions and food vacuoles, while the smaller thin-walled cells contain nuclei or look empty. Only the thin-walled cells are found to germinate. The thick-walled cells, with their stored food, appear to serve a double role of protection of, and as a source of, food for the thin-walled cells.