Ultrastructural changes in the yeast Candida lipolytica caused by penetration of hydrocarbons into the cell

Visualization of yeast cells by electron microscopy

In the 1970s, hydrocarbon or methanol utilizable yeasts were considered as a material for foods and ethanol production. During the course of studies into the physiology of yeasts, we found that these systems provide a suitable model for the biogenesis and ultrastructure research of microbodies (peroxisomes). Microbodies of hydrocarbon utilizing Candida tropicalis multiply profusely from the preexisting microbody. β oxidation enzymes in the microbody were determined by means of immunoelectron microscopy. We examined the ultrastructure of Candida boidinii microbodies grown on methanol, and found a composite crystalloid of two enzymes, alcohol oxidase and catalase, by analyzing using the optical diffraction and filtering technique and computer simulation. We established methods for preparing the protoplasts of Schizosaccharomyces pombe and conditions for the complete regeneration of the cell wall. The dynamic process of cell wall formation was clarified through our study of the protoplasts, using an improved ultra high resolution (UHR) FESEM S-900 and an S-900LV. It was found that β-1,3-glucan, β-1,6-glucan and α-1,3-glucan, as well as α-galactomannan, are ingredients of the cell wall. The process of septum formation during cell division was examined after cryo-fixation by high pressure freezing (HPF). It was also found that α-1,3- and β-1,3-glucans were located in the invaginating nascent septum, and later, highly branched β-1,6-glucan also appeared on the second septum. The micro-sampling method, using a focused ion beam (FIB), has been applied to our yeast cell wall research. A combination of FIB and scanning transmission electron microscopy is useful in constructing 3D images and analyzing the molecular architecture of cells, as well as for electron tomography of thick sections of biological specimens.

Effects of compressed unsaturated hydrocarbon gases on yeast growth

The effect of compressed unsaturated hydrocarbon gases on the growth of the yeast Saccharomyces cerevisiae was investigated by microcalorimetry. The growth thermograms showed that unsaturated hydrocarbon gases inhibited yeast growth. As an approach to determining the comparative toxicity of unsaturated hydrocarbon gases, we determined the 50% inhibitory pressure (IP(50)) and the minimum inhibitory pressure (MIP). On the basis of the IP(50) and MIP values, the inhibitory potency of the gases increased in the order ethylene < propylene < 1-butene. Additionally, scanning electron microscopy showed that cells treated with unsaturated hydrocarbon gases were damaged, including invagination of the cell surface.

Fatty acid accumulation in the yeast Sporidiobolus salmonicolor during batch production of gamma-decalactone

This paper provides new information about the metabolism of various fatty acids and gamma-decalactone production by yeast. An analysis of the fatty acid composition of the yeast Sporidiobolus salmonicolor during batch production of lactone with ricinoleic acid methyl ester as a precursor showed an accumulation of the gamma-decalactone precursor inside the cells. Electron microscopy of the yeasts showed the presence of large internal inclusions leading to membrane and organelle lysis and, consequently, death of the yeast. S. salmonicolor cultivated with methyl oleate did not produce gamma-decalactone and is viable during the whole culture. Analysis of the long chain fatty acid fraction showed incorporation of methyl oleate.

Sorption and Metabolism of Metolachlor by a Bacterial Community

A stable bacterial community absorbed and transformed the herbicide metolachlor [2-chloro- N -(2-ethyl- 6-methylphenyl)- N -(2-methoxy-1-methylethyl)-acetamide] from a liquid medium. About 80% of the added ring-[U- 14 C]metolachlor (50 μg/ml) disappeared from the medium and accumulated inside the cells. The ratio of cellular 14 C to 14 C in 1 mg of supernatant reached a value of 1.1 × 10 4 in a 10-day-old culture. 14 C remaining in the medium consisted primarily of two dechlorinated products of metolachlor with m/z 233 and 263 as determined by mass spectrometry. The 14 C-labeled material absorbed by the cells was strongly bound; only 2% of the 14 C was released into deionized water after shaking for 3 h. Approximately 96% of the 14 C associated with the biomass was extracted with acetone, and high-performance liquid chromatographic analysis of this fraction showed six peaks containing radioactivity. Since no metolachlor was detected by chromatographic analysis, it was concluded that the radioactivity recovered from the cells represented transformed products of metolachlor. Pure cultures isolated from the bacterial mixed culture were less effective in transforming and accumulating metolachlor. These results suggest that it may be advantageous to seed an aquatic environment with a mixture of microorganisms, rather than individual microbial species, as a method for removal or detoxification of metolachlor.

Metabolism of n-alkanes by Aspergillus japonicus

Cells of Aspergillus japonicus could degrade n-alkanes as a sole source of carbon. One of the pathways operative during the degradative process was the terminal pathway. Electron micrographs showed that the hydrocarbons were present in the cells as microdroplets.

Influence of oxygen on the microsomal electron transport system in Saccharomyces cerevisiae

The influence of oxygen on the level of microsomal electron transport chain components has been studied during the growth of Saccharomyces cerevisiae. Enzyme activities and cytochrome content were assayed in microsomal fractions prepared from a protoplast lysate free from mitochondrial contamination. It was found that the cytochrome P-450 and cytochrome b5 content, to get her with the NADPH-cytochrome (P-450)-reductase and NADH-cytochrome (b5)-reductase activities, were increased in the cells as the pO2 of the medium was decreasing. At the same time an increase in the membrane surface of the endoplasmic reticulum can be observed.

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.

[Effect of carbon source on the Candida spec. H energy reserve metabolism]

Various aspects of the carbon energy metabolism of Candida spec. H on glucose in comparison to its metabolism on hydrocarbons were studied in this article. In the absence of nitrogen for growth cells undergo several changes in their chemical composition. The content of protein and nuclei acids decreases rapidly. At the same time on the glucose medium glycogen and trehalose were markedly accumulated, whereas lipid accumulation was only slight. On the hydrocarbon substrate both carbohydrates and lipid were increased. Also the difference between the fatty acid composition of Candida spec. H when grown on glucose and on n-alkanes was studied. The results were discussed.

Ultrastructure of methanotrophic yeasts

The cellular structure of two yeast strains capable of growth on methane was investigated by electron microscopy. Microbodies were observed in cells of Sporobolomyces roseus strain Y and Rhodotorula glutinis strain CY when grown on methane but rarely when grown on glucose. The size of the microbodies and the number observed per cell in a thin section did not increase with culture age. No crystalline organization was observed within these organelles. Similar microbodies were also observed in cells of R. glutinis CY grown on hexadecane. The plasma membranes of both methane and hexadecane-grown cells exhibited increased invagination compared to that of glucose-grown cells. Catalase activity was detected in the microbodies of alkane-grown cells by using 3,3'-diaminobenzidine as a cytochemical stain. The data presented suggest that microbodies, and the catalase contained within them, play a role in eucaryotic methane metabolism.

Chemical and structural alterations at the cell surface of Candida tropicalis, induced by hydrocarbon substrate

The surface-localized polysaccharide of alkane-grown cells of Candida tropicalis was identified as mannan containing approximately 4% covalently linked fatty acids. Glucose-grown cells lacked the mannan-fatty acid complex. The surface structure of alkane-grown cells showed a radial arrangement of the wall polymers, with protruding parts. The cell surface of glucose-grown cells was smooth, with a coherent outer limit. The mannan was localized by using concanavalin A. Masking of the mannan with concanavalin A reduced the binding affinity of the surface for alkane, indicating the involvement of the surface-localized mannan-fatty acid complex in the binding of alkanes.

Characterization of intracytoplasmic hydrocarbon inclusions from the hydrocarbon-oxidizing Acinetobacter species HO1-N

The ultrastructure of Acinetobacter sp. strain HO1-N grown on hydrocarbon and nonhydrocarbon substrates was compared using thin sections and freeze-etching. Hydrocarbon-grown cells were characterized by the presence of intracytoplasmic membrane-bound hexadecane inclusions. This membrane did not exhibit a typical unit membrane structure but appeared as a monolayer. The freeze-etch technique revealed the internal structure of the hexadecane inclusions and provided evidence for the presence of a smooth-surfaced limiting membrane. Freeze-etching also revealed intracytoplasmic membranes in the hexadecane-grown cells. These ultrastructural modifications were not present in nonhydrocarbon-grown cells. The hexadecane inclusions were isolated from Acinetobacter. Negative-staining of the inclusions revealed electron-transparent vesicles approximating the size of the inclusions seen in whole cells. Freeze-etching of the purified inclusions revealed membrane-bound vesicles. The purified inclusions exhibited a relatively high value of lipid phosphorus to protein. The lipid composition and the electrophoretic banding pattern of the inclusions on sodium dodecyl sulfate-polyacrylamide gels were determined and compared with other membrane fractions (outer membrane and cytoplasmic membrane) previously isolated from this organism.

Microbial assimilation of hydrocarbons. I. The fine-structure of a hydrocarbon oxidizing Acinetobacter sp

1. The fine-structure analysis of the hydrocarbon oxidizing microorganism, Acinetobacter sp., demonstrated a cytoplasmic modification resulting from growth on paraffinic and olefinic hydrocarbons. 2. Intracytoplasmic hydrocarbon inclusions were documented by electron microscopy with chemical identifications obtained by gas chromatography and X-ray diffraction. 3. These results demonstrate the ability of a microorganism to accumulate hydrocarbon substrates intracellularly which, in turn, indicates the transport across the cell membrane.