Structure of the cell surface of the yeast Candida tropicalis and its relation to hydrocarbon transport

The surface structure of the hydrocarbon-utilizing yeast Candida tropicalis was investigated by scanning and transmission electron microscopy (SEM and TEM respectively). The sample preparation technique was based on a rapid cryofixation without any addition of cryoprotectants. In subsequently freeze-dried samples the surface structure was analysed by scanning electron microscopy. Thin sections were prepared from freeze substituted samples. Both techniques revealed hair-like structures at the surface of hydrocarbon-grown cells. The hairy surface structure of the cells was less expressed in glucose-grown cells and it was absent completely after proteolytic digestion of the cells. When cells were incubated with hexadecane prior to cryofixation a contrast-rich region occurred in the hair fringe of thin sections as revealed by TEM. Since these structures were characteristic for hexadecane-grown cells and could not be detected in glucose-grown or protease-treated cells it was concluded that they originate from hexadecane adhering to the cell surface and are functionally related to hexadecane transport. The structure of the surface and its relation to hydrocarbon transport are discussed in view of earlier results on the chemical composition of the surface layer of the cell wall.

[Effect of emulsifiers released by yeasts multiplying on n-alkane media on their growth and microscopic organization]

Bioemulsifiers and ether extracts from the cultural broth of yeast cells were used to study their effect of Candida lipolytica growth and ultrastructural organisation. When the emulsifiers and ether extracts were added to the growth medium, the lag phase was reduced but the growth rate did not change. The ether extracts increased the growth rate of C. lipolytica 374/2 and the final biomass yield of C. lipolytica 704. The ultrastructural organisation of C. lipolytica 374/2 cells changed under the action of the bioemulsifier added to the growth medium.

[Alcohol oxidation by Candida guilliermondii yeasts grown on hexadecanol]

A number of enzyme systems involved in the first steps of hexadecane oxidation can be induced by hexadecanol, an intermediate product of hexadecane degradation. It has also been found that, in Candida guilliermondii cells and in their mitochondrial fraction, an oxidase system is induced when the cells are grown on hexadecanol. This system is similar to that in cells grown on hexadecane; it oxidises higher alcohols at a high rate and is not inhibited by the inhibitors of the man phosphorylating respiration chain. The membrane-bound alcohol dehydrogenase and aldehyde dehydrogenase activities resistant to pyrazole, an inhibitor of cytosol ethanol dehydrogenase, are induced together with the oxidase activity when the cells are grown on hexadecanol as well as on hexadecane. The oxidation of higher alcohols by whole cells is entirely inhibited by azide although their oxidation by mitochondria is resistant to the action of azide; apparently, azide inhibits the transport of alcohols into the cell.

Scanning and transmission electron microscopy of in situ bacterial colonization of intravenous and intraarterial catheters

Intravenous and intraarterial catheters were examined microbiologically and morphologically. Bacteria or yeasts were recovered from 38 of the 63 catheters examined, and Staphylococcus epidermidis was present on 29 of the 38 colonized catheters. Examination of unused Teflon catheters ( Jelco ; Surgikos , Inc., Peterborough , Ontario, Canada) showed surface irregularities, and the examination of colonized intravascular catheters recovered from patients showed very extensive amorphous accretions on both their lumenal and external plastic surfaces. Detailed scanning electron microscope examination of the accretions on vascular catheters from which S. epidermidis had been isolated showed (ca. 0.8 micron) coccoid bacteria within confluent biofilms , in which they were enveloped by amorphous material. Transmission electron microscope examination of these same accretions revealed coccoid cells (ca. 0.8 micron) with a gram-positive cell wall structure living in fibrous matrix-enclosed microcolonies in spaces between squamous epithelial cells. Staphylococcus aureus biofilms were seen to contain coccoid cells (ca. 1 micron) in a very extensive amorphous matrix, and a Candida parapsilosis biofilm contained very large numbers of large coccoid cells (ca. 4.3 microns) in a fibrous matrix resembling fibrin. Cells of a Corynebacterium species appeared to form much less extensive matrix-enclosed microcolonies on the colonized plastic surface. These data indicate bacteria and yeasts colonize intravascular catheters by an adherent biofilm mode of growth on these plastic surfaces.

[Changes in the orientation of the fracture plane of cell membranes during freeze-fracturing as an index of change in membrane structure]

Using freeze-fracture method it is shown that the direction of the fracture plane is a sensitive indicator of the membrane structural organization. A decrease in the proportion of longitudinal fractures is noted upon the membrane rearrangement presumably associated with changes in the lipid phase, and, on the contrary, an increase in the proportion of these fractures is observed upon some actions resulting, presumably, in changes of the protein phase of membranes.

[Structural organization of the cell walls in yeasts of the genus Candida]

The structural organization of the outer layer of cell walls was studied in three species of the Candida genus using a proteolytic digestion followed by an analysis of the resultant cell wall fragments by the techniques of gel filtration and PMR. Differences were found in the thickness of the outer cell wall layer removed by proteases as well as in the structural arrangement of polysaccharide molecules in this layer.

Significance of yeast peroxisomes in the metabolism of choline and ethanolamine

The yeasts Candida utilis and Hansenula polymorpha were able to grow in media containing choline or ethanolamine as the sole nitrogen source. During growth in the presence of these substrates, large peroxisomes developed in the cells, and extracts of choline-grown C. utilis cells contained increased levels of amine oxidase and catalase. Incubation of whole cells with choline in the presence of the amine oxidase inhibitor aminoacetonitrile led to excretion of dimethylamine and methylamine. Cytochemical experiments in which spheroplasts prepared from choline-grown cells were incubated with CeCl3 and choline, trimethylamine, dimethylamine or methylamine revealed positively stained peroxisomes, whereas in the presence of 1 mM aminoacetonitrile staining was not observed. This indicated that choline was degraded via methylated amines and that peroxisomes played a role in its metabolism. A similar involvement of peroxisomes in choline degradation was observed in H. polymorpha. Cell-free extracts of ethanolamine-grown C. utilis and H. polymorpha also contained increased levels of amine oxidase and catalase. Ethanolamine was oxidized by cell-free extracts of both organisms after growth in the presence of ethanolamine or choline. Incubation of spheroplasts of ethanolamine- or choline-grown C. utilis with CeCl3 and ethanolamine resulted in positively stained peroxisomes. In this organism peroxisomes were therefore also involved in ethanolamine degradation.

[Ultrastructure of Candida utilis in continuous culture with various concentrations of the carbon source introduced by different technics]

The object of the work was to study changes in the ultrastructure of Candida utilis cells induced by increasing concentrations of glucose during chemostat cultivation and continuous cultivation with glucose pulse feeding. The results indicate that the cell structure and metabolism change vectorially with an increase of glucose concentration regardless of how glucose was added. An increase of the input glucose concentration is followed by an increase in the periplasmic space, the content of glycogen, the length and diameter of mitochondria, and the size of the nucleus. However, in the case of glucose pulse feeding, the above changes in the cell structure occur at a considerably lower input concentration as compared to the chemostat culture. Under these conditions, microtubuli are assembled in the cytoplasm in response to the glucose stimulus.

[Effect of sulfur-containing compounds on the ultrastructural organization of the cell wall of Candida utilis yeasts]

The effect of sulfur-containing compounds (cysteine, homocysteine, glutathione, cystine, and methionine) on the ultrastructural organization of the cell wall was studied in Candida utilis 295t by electron microscopy with the aid of staining SH groups by HgCl2. Treatment of the cells with cysteine and homocysteine was found to modify the ultrastructure of the cell wall: the capsule was damaged and the porosity increased, which facilitated the penetration of these compounds into the periplasm. Their further conversion in the cell has been studied.

An investigation into the feasibility of using azide-insensitive ATPase and ConA as yeast plasma membrane markers

Cytochemical localization of Concanavalin A binding sites in protoplasts of Candida tropicalis, investigated with glycosylated-ferritin and electron microscopy, showed that the lectin was specifically bound to the external protoplast surface. Thus, the plasma membranes have been labelled with 125I-Concanavalin A and followed through the isolation procedure. Relative distribution of 125I-radioactivity and azide-insensitive ATPase activity in the obtained fractions, suggested that this enzyme was an equivocal plasma membrane marker. Despite the presence of internal Concanavalin A binding sites, Concanavalin A could be used unambiguously as an exogenous plasma membrane marker of intact protoplasts.

Absence of DNA in peroxisomes of Candida tropicalis

Yeast peroxisomes were purified to near homogeneity from cells of Candida tropicalis grown on oleic acid for the purpose of examining the possible presence of DNA in this organelle. The purification procedure includes the effective conversion of cells to spheroplasts with Zymolyase and sodium sulfite and the separation of the organelles at extremely low ionic strength. The mitochondrial contamination was less than 1%, based on several criteria, and the yield of peroxisomes was about 40%. The purified peroxisomal fraction contained a very small amount of DNA, which yielded restriction fragments indistinguishable from those of mitochondrial DNA. The absence of DNA in peroxisomes was also supported by cesium chloride density gradient centrifugation of the organelles lysed with a detergent, staining of the organelles with a fluorescent dye specific to DNA, and labeling of the DNA with [3H]adenine.

Immunological changes after long-term feeding of germfree piglets with protein isolates and yeast cell walls from Candida utilis as food additives

Germfree piglets were fed a diet supplemented with cell walls and a protein isolate from Candida utilis for 54 days. Besides morphological signs of activation of the lymphoid tissue which occurred primarily in the intestine of piglets which had been fed yeast cell walls, even an increased serum immunoglobulin level could be detected. In sera and intestinal content of piglets fed both with cell walls and isolated protein, specific antibodies capable of agglutinating yeasts were present. Even though a limited number of experimental animals was employed it can be concluded that the yeast material added to the diet elicited an immune response.

The effects of naftifine on the ultrastructure of Candida parapsilosis: a freeze fracture study

Naftifine, a new antimycotic drug, was found to induce dose-dependent ultrastructural changes in C. parapsilosis. Increased accumulation of lipid particles in the cytoplasm, thickening of the cell wall and alterations of the plasma membrane by vesicular structures were the most obvious findings. Vesicular inclusions have also been observed in the cell wall. These changes caused a progressive destruction of the cell architecture which is presumed to result from interaction of naftifine with fungal sterol biosynthesis.

[Polysaccharide structure of cell wall preparations from the food protein yeast Candida spec. H]

More than 27% of the cell wall are unstably bound components: Proteophosphomannan as a main polysaccharide of the cell wall, mannose and manno-oligosides which are bound to peptides or phosphate. 19% are glycosidically linked with a phosphate bridge or O-glycosidically (Ser/Thr) linked with the protein which is covalently bound to the cell wall. Besides mannose and glucose, manno-oligosides and gluco-oligosides are involved in this linkage. A preparation consisting of glucan and chitin remains after careful degradation. It contains (1,2)-, (1,3)- and (1,6)- linked glucose, (1, 2, 3)-, (1, 2, 6)- or (1, 3, 6)-glucose-branchpoints and (1,4)-linked N-acetylglucosamine.

[Submicroscopic surface organization of Candida lipolytica cells growing on hexadecane]

The ultrastructure of the cell wall surface was studied in two Candida lipolytica strains, IBPhM-160 (704) and 1, during their growth on hexadecane, using the technique of ultrathin sections. Linear three-layer membranes, membrane vesicles and complicated membrane complexes were shown to appear on the surface of the cell walls when the yeast strains were grown on hexadecane. The rate of membrane formation was greater in the cells of strain 1, and increased in the both strains by the stationary growth phase. Since no cells underwent lysis at any of the growth phases studied, the formation of membrane complexes on the yeast cell wall should reflect the reconstruction of the surface of morphologically intact cells grown on hexadecane.

Ultrastructural alterations at the cell wall and plasma membrane of Candida spec. H induced by n-alkane assimilation

The ultrastructure of n-alkane-grown cells of Candida spec. H was investigated by thin sectioning and freeze-etching techniques. On the plasma membrane shallow depressions could be observed. n-Alkane deposits were localized within the cell wall and at the plasma membrane. Peri-plasmic multilamellar structure appear in connection with n-alkane accumulation. Their participation in hydrocarbon assimilation and the nature of the lamellar structures are discussed.

[Mannan localization with concanavalin A in conjunction with electron microscopy and chemical analysis of differently prepared cell walls of the food protein yeast Candida spec. H]

Regions of different electron densities after concanavalin A-peroxidase-reaction have been observed in cell walls of intact cells as well as in isolated cell walls: In the peripheral region of intact cell walls two mannan layers appear. Treating isolated cell wall with pronase, NaOH, ethylendiamine or citrate buffer, respectively, we find on A binding spots in the inner cell wall regions which appear electron transparent in the untreated cell walls. Apparently the mannan component of the inner cell wall regions is masked by proteins. In correspondence with chemical analysis our results cannot confirm the existence of inner cell wall regions which are free of mannan.

[Cytobiochemical characteristics of Candida boidinii in continuous culture on methanol and HCO3-]

The cytological and biochemical characteristics of the yeast Candida boidinii KDI were studied under the conditions of continuous cultivation in media containing methanol in the presence of exogenous bicarbonate and without it. Bicarbonate addition was found to cause a decrease in the activity of catalase, a reorganization of the peroxisomes, and an increase in the activity of pyruvate and phosphoenolpyruvate carboxylases, the enzymes involved in heterotrophic assimilation of carbon dioxide.

Comparison of the mannan structure from the cell-wall mutant Candida sp. M-7002 and its wild type. I. Characterization of the proteo-mannan from the mutant and the wild-type cells

The cell-wall mutant of a hydrocarbon-assimilating yeast, Candida sp. M-7002 and its wild type have shown a significant difference in mannose content. Each mannan was isolated from the mutant and the wild-type cells by fractionation with Cetavlon and copper reagent. Both mannans contain D-mannose, D-glucose and phosphate. The mutant mannan has a relatively high content of protein (18% in weight bases) whereas the wild-type mannan has a low protein content (5.1%) with a high amount of carbohydrate (greater than 90%). Structural analyses by enzymatic and chemical methods showed that both mannans had a mannosidic (alpha 1--6)-linked back bone substituted at O-2 by side chains of varying length. The side chains of the mutant mannan were shown to consist of single mannose units and disaccharide units whose linkages were predominantly alpha 1--2, while the wild-type mannan had two additional side chains of disaccharides. These additional side chains had alpha 1--3 linkages which were scarcely found in the mutant mannan. beta-Elimination reaction demonstrated that the mannans also contain mannosyl oligosaccharides linked to protein through O-glycosidic linkage. The chemical properties of the mannan of the Candida mutant indicates that the mutation might occur not only in the side chain structure but also in the (alpha 1--6)-linked mannan back bone.