13C Fourier transform nuclear magnetic resonance studies of fractionated Candida utilis membranes

13C Fourier transform nuclear magnetic resonance has been used to study the lipid structure and dynamics of fractionated Candida utilis cell membranes. Measurements of the spin-lattice relaxation times indicate the existence of mobility gradients in the direction of increased mobility from the glycerol backbone toward the terminal methyl group of the fatty acid and toward the choline methyls. The temperature dependence of the relaxation times gives activation energies of approximately 4-6 kcal/mol for the rotations about various carbon-carbon bonds which determine the relaxation rates. In general, comparison with data which have been reported for artificial membrane systems indicates that the contributions of protein-lipid interactions to the T1 gradient are of negligible importance in the yeast membrane system. A dynamical model for the motion about bonds near unsaturated bonds which determined the relaxation of the unsaturated carbons is also proposed. Measurements of chemical shifts with temperature also exhibit a correlation with chain position. On the basis of these data a correlation of deltaE, the energy difference between gauche and anti conformations for gamma carboms, with chain position is inferred. In addition, an estimate of 1.2 kcal/mol can be obtained for deltaE for carbons near the end of the fatty acid chain. This value indicates that intermolecular interactions contribute substantially to deltaE since a value of approximately 0.5 kcal/mol can be ascribed to intramolecular interactions.

YATP value in Candida tropicalis grown on n-alkanes, fatty acids, and acetate

The amount of ATP produced during n-alkane, fatty acid, or acetate metabolism in Candida tropicalis has been established from the P/O ratios measured on isolated mitochondria, yield on substrate and carbon balance. For these three kinds of substrates YATP value has been found to be close to 4, although Ysub on acetate is very different from those found with n-alkanes or fatty acids.

The morphology of colony variants of three species of Candida

The colonies of 12 isolates of 3 Candida spp. with variant colony forms were studied by scanning and transmission electron microscopy. Small colonies were formed by 4 isolates each of C. albicans and C. parapsilosis and by 1 of C. tropicalis. These had an abnormally high proportion of degenerate yeast cells with an associated increase in granular cytoplasmic material intercellularly. The increased matrix in these small colonies formed a thick superficial coat over the organisms. Rough colonies were formed by 1 isolate each of C. albicans, C. tropicalis and C. parapsilosis. The convoluted regions of these colonies contained many pseudohyphal cells but few degenerate cells and little granular or fibrillar material in their intercellular matrices. The shape of colonies of Candida spp. may be altered by variations in the viability or the morphology of the organisms.

Alcohol oxidase and catalase in peroxisomes of methanol-grown Candida boidinii

Microbodies, designated as peroxisomes because of their enzyme complement, have been isolated from methanol-grown cells of Candida boidinii. Spheroplast lysates were separated on non-continuous Ficoll density gradients, resulting in a mitochondrial fraction and a peroxisome fraction. Estimates of purity using the mitochondrial enzyme markers suggested that the contamination of mitochondria in the peroxisome fraction was about 2-3%. As shown by electron microscopy the peroxisomes were 0.4-0.6 mum in diameter and contained crystalloid inclusions. Alcohol oxidase and catalase, which catalyse the oxidation of methanol to formaldehyde in Candida boidinii, could be localized within the peroxisomes. Gel-electrophoretic studies of the peroxisome fraction demonstrated that it contained only two predominant protein bands consistent with alcohol oxidase and catalase. No alcohol oxidase and catalase activity was found in mitochondria.

Mitochondrial structure studied by high voltage electron microscopy of thick sections of Candida utilis

Mitochondrial structure in yeast cells under various physiological conditions has been studied by high voltage electron microscopy of sections that are 0-5 to 2-0 mum thick. Such thick sections of the yeast Candida utilis had a small number of long, branched tubular mitochondria per cell. The mitochondria extended into cell buds and unseparated daughter cells. It was apparent from parallel studies with thin sections that most of the rounded mitochondrial profiles viewed in thin sections should not be interpreted as being numerous small individual mitochondria. Attempts to study thick sections of the yeasts Saccharomyces cerevisiae and Schizossaccharomyces pombe were frustrated by poor contrast.

Colloidal gold granules as markers for cell surface receptors in the scanning electron microscope

A rapid method has been developed to visualize cell surface receptors in the SEM. Thus mannan at the surface of Candida utilis cells was localized by stabilized colloidal gold granules coated with either anti-mannan antibodies or Con A.

Evaluation of the Uni-Yeast-Tek kit for the identification of medically important yeasts

The Uni-Yeast-Tek system, a commercially prepared kit and scheme for the rapid identification of medically important yeasts (Corning Medical), was evaluated in comparison with a conventional procedure in the identification of 623 yeasts. The system permitted the presumptive identification of 99.8% of 436 isolates representing 16 common species commonly isolated in the clinical laboratory. Correct biochemical and morphological analyses were obtained with 48 other species, but their specific identification required additional data.

Intercellular matrix in colonies of Candida

The histochemistry and fine structure of typical colonies of six species of Candida were studied, using a total of 31 clinical isolates. The colonies consisted of viable and degenerate cells which lay in an intercellular matrix. This matrix was made up of amorphous, granular, and fibrillar components, the relative proportions and total amount of which varied from species to species. The cells of all species were surrounded by a zone of homogeneous amorphus material, which may be a highly cross-linked carbohydrate. This separated intact cells from irregularly distributed granular debris derived from the cytoplasm of degenerate cells. Focal cellular degeneration and associated granular debris were present within the colonies of all species and were most common in the surface layers of cells of colonies of C. albicans and C. tropicalis. The large amounts of intercellular matrix in this region formed a surface coat on colonies of these two species. Intercellular strands of cell wall material, and to a lesser extent other membranous elements from degenerate cells, formed a prominent fibrillar meshwork in the colonies of C. albicans and C. tropicalis, but were less common in those of C. pseudotropicalis and C. guilliermondii and seldom seen in those of C. parapsilosis and C. krusei.

[Structure of Candida tropicalis K-41 thermotolerant yeasts at various growing temperatures on a mineral medium with hydrocarbons]

In the C. tropicalis K-41 cells fixed by glutaraldehyde and osmium most membranes consisted of two electron-transparent and one electron-dense layer. Morphologo-structural peculiarities of the cell fraction grown at 39 degrees testify to a certain disconnection of energetic and constructive metabolism, inhibition of synthetic processes. Cell division was more active at 29 degrees.

[Primary distribution of n-alkane through the structures of yeast cells]

When n-alkane enters the cells as a result of molecular sorption and diffusion, it is distributed within all membrane structures of the cell (microsomes, mitochondria, membranes, vacuoles, cytoplasmic membranes, and cell walls). Sorption of n-alkane by all these structures in vivo comes at equilibrium after incubation of the cells with n-alkane during 3-4 min. Accumulation of the hydrocarbon in the morphological fractions of the cell depends on its concentration in the incubation medium. Isotherms of the sorption are convex curves. Sorption power, maximum sorption capacity, affinity and strength of the bonds with the hydrocarbon differ among the membrane structures of the cell. The maximum capacity of sorption of n-alkane by the structures does not correlate with the content of lipids and phospholipids in the structures. Sorption of n-alkanes is presumed to depend on the structural organization of lipids in the morphological fractions.

The ultrastructure of Candida krusei

Various methods of chemical fixation and freeze-drying of Candida krusei were compared to determine the most appropriate method for the ultrastructural investigation of the thick walled organisms of this genus. Freeze-drying without chemical fixation was of little value because of insufficient variation in electron density. Potassium permanganate was able to penetrate the intact cell but failed to show cytoplasmic glycogen and lipid and some details of the cell wall. While normal glutaraldehyde, formaldehyde and osmium tetroxide treatment failed to permeate and preserve intracellular structures, several cycles of rapid freezing (- 155 degrees C) and thawing followed by glutaraldehyde fixation and osmium tetroxide post-fixation demonstrated the intracellular details of the majority of cells so treated.

Ultrastructure of methanol-utilizing yeast cells: appearance of microbodies in relation to high catalase activity

Nine strains of methanol-utilizing yeasts belonging to the genera Candida, Hansenula, Kloeckera, Pichia, and Torulopsis were examined with respect to the interrelationship between their catalase content and ultrastructure. Methanol-grown cells of all the yeasts tested showed higher catalase activities than the respective ethanol- and glucose-grown cells. In connection with this, occurrence of a specific organelle surrounded by a single-unit membrane ("microbodies") was observed only in the methanol-grown cells. Several morphological differences were observed between the microbodies of methanol-utilizing yeasts and those of hydrocarbon-utilizing yeasts such as Candida tropicalis. That is, microbodies of methanol utilizers were large in size, existed in closely associated forms, and had crystalloid structures. Localization of catalase activity in these microbodies was demonstrated cytochemically by use of 3,3'-diaminobenzidene. Especially, 3,3'-diaminobenzidine reaction product accumulated heavily in crystalloids of yeast microbodies.

Comparison of the survival and metabolic activity of psychrophilic and mesophilic yeasts subjected to freeze-thaw stress

A mesophilic yeast, Candida utilis, and a psychrophilic yeast, Leucosporidium stokesii, were subjected to freeze-thaw cycling over the range 25 to -60 C. Viability after freeze-thaw stress was directly correlated with the rate of cooling and the physiological age of the cultures. Rates of glucose fermentation and oxidation could be directly correlated with viability. The optimal cooling rate for both yeast strains was 4.5 to 6.5 C/min; however, their levels of survival obtained at this optimal cooling rate varied considerably. In addition, the psychrophile was less resistant to freeze-thaw stress than was the mesophile.

Microbiodies in methanol-grown Candida boidinii

Intracellular structures were observed in Candida boidinii grown in a medium containing methanol as the sole source of carbon and energy; these structures were absent in the same organism grown in the presence of glucose or ethanol. These substrate-specific structures are ultrastructurally similar to microbodies. Studies with sphaeroplast and a mutant lacking alcohol-oxidase activity indicate that the alcohol may be located in these microbodies.

[Sensitivity and resistance of Candida to 5-fluorocytosine. Relationship to the cell wall ultrastructure]

The study of ultrafine sections of the yeasts of Candida show a difference in the cell between sensitive and resistant strains to 5-fluorocytosine (5-FC). The sensitive strains show a thin border of granular material inside of the clear internal layer which is absent for the majority of resistant strains. After trypsinization, the sensitive strains show a resistance which is reversible and the granular layer disappears. These data permit the conclusion that the middle layer of resistant strains is of protein nature and interferes with the metabolization of 5-FC.

[Electron microscopic study of Candida tropicalis yeasts grown on a medium containing selenium]

The yeast Candida tropicalis 303 was cultivated on a medium containing selenium, and studied by electron microscopy. The vacuoles of these cells contained electron-dense granules. The correlation between the increase in the number of the electron-dense granules in the cells of C. tropicalis 303 and the biomass suggests the presence of Se0 in the Granules.

[Comparative study of the ultrastructural characteristics of Torulopsis candida yeasts grown on glucose and hexadecane]

Electron-microscopic examination of the ultrastructure of Torulopsis candida cells grown on glucose and hexadecane revealed a well-developed network of canals in the cell wall of yeasts grown on hexadecane. These canals appeared in the non-adapted cells at the initial hours of the cultivation and completed their formation at the end of the logarithmic phase. The investigation by the freeze-etching showed the exocytosis of "secretory granules" to take place at the periplasma of the cells, and the morphological relationship of the granules to the canals in the cell wall.

Microbodies in methanol-assimilating yeasts

Cells of 3 yeast species capable of assimilating methanol have been examined by electron microscopy. When grown on methanol as the sole source of carbon and energy they contained many microbodies. Cells grown on glucose or ethanol either did not contain such bodies at all, or only to a limited extent.