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The cell wall of the yeast form of Histoplasma farciminosum contains 13.2% β-1,3-glucan, 1.0% galactomannan, and 25.8% chitin, whereas the cell wall of mycelial form has 21.8, 4.5, and 40%, respectively, for the same polymers. Also, the cell wall of the yeast form contains α-1,3-glucan (13.5%) and an unidentified polymer (21.5%). Chitin, one of the structural polymers of both yeast and mycelial cell walls, is identified as thin isolated fibers (4 nm wide) or in thick bundles (50 nm wide) of fibers. β-(1-3)-Glucan is also found as thin isolated fibers indistinguishable from isolated fibers of chitin. Fibers 14 nm wide and resembling α-(1-3)-glucan fibers of other fungi are found in the yeast form. The results reported here do not give support to the proposal for a different taxonomic classification.

A comparative study of the mycelial phase ofParacoccidioides brasiliensisandBlastomyces dermatitidisreveals that both fungi are very much alike, containing multiple nuclei and nuclear pores, mitochondria, ribosomes, scarce endoplasmic reticulum, intracytoplasmic membrane systems, glycogen, and vacuoles. Shadowed cell walls show fine fibrillar surfaces that contrast with those in the yeast phase. The intracytoplasmic membrane system is continuous with the plasma membrane and is similar to bacterial mesosomes. Granules with light cores and dark rims are observed in the plasma membrane. Live hyphae growing inside a dead hypha are found much more frequently in immersed cultures than in solid-medium cultures, suggesting that breakage of the hypha could elicit this phenomenon.

Short and thick fibers were observed on the outer surface of the yeast phase of Paracoccidioides brasiliensis , and long and thin fibers were seen on the inner surface. The long fibers disappear with chitinase treatment and are composed of chitin. The short fibers disappear under alkali treatment and are composed of α-glucan. Comparisons with α-(1 → 3)-glucan isolated from Aspergillus niger and Polyporus betulinus and with chitin from fungal origin support our point of view.

The biochemical and morphological changes of the yeastlike (Y) form to the mycelial (M) form of Paracoccidioides brasiliensis were examined. The main polysaccharide of hexoses of the Y-form cell wall was α-glucan, whereas the polysaccharides of the M-form cell wall were β-glucan and galactomannan. The α-glucan of the Y form contained mainly α-(1 → 3)-glycosidic linkage. The β-glucan of the M form contained mainly β-(1 → 3)-glycosidic linkage with a few branches at C-6 position. The incorporation of 14 C-glucose into the cell wall glucans showed that synthesis of α-glucan decreased rapidly after the temperature of the culture was changed from 37 to 20 C. The synthesis of β-glucan was augmented at an early stage of the morphological change. The M-form cell wall contained 12 times more disulfide linkage than the Y form. The cell-free extracts of the whole cell of the Y form had five times more protein disulfide reductase activity than the M form, whereas extracts of the M form contained five to eight times more β-glucanase activity than the Y form. From these results, a hypothesis for the production of the M form from the Y form is proposed.

Glucans were isolated from the cell wall of the yeast (Y) and mycelial (M) forms of Paracoccidioides brasiliensis . The alkali-soluble glucan of the Y form had properties of α-1,3-glucan. The alkali-insoluble glucan of the M form was identified as a β-glucan which contains a β-(1 → 3)-glycosidic linkage by infrared absorption spectrum, by effect of β-1,3-glucanase, and by partial acid hydrolysis. The alkali-soluble glucans of the M form were a mixture of α- and β-glucans and the ratio of α- to β-glucan was variable, depending on the preparations.

The thermally induced changes in the cell wall polysaccharides of Blastomyces dermatitidis strain BD64, which produces a yeastlike form (Y form) at 37 C and a mycelial form (M form) at 20 C, were examined. The cell walls of the Y and M forms contained 36 and 51% of hexoses, respectively. The M-form cell wall contained glucose, galactose, and mannose in a molar ratio of 1:0.1:0.2. The Y-form cell wall contained mainly glucose and a very small amount of galactose and mannose. The glucans of the cell wall of the Y form consisted of about 95% α-glucan and 5% β-glucan, whereas those of the M-form cell wall consisted of about 60% α-glucan and 40% β-glucan.

The difference between the budding process of Paracoccidioides brasiliensis and Blastomyces dermatitidis is reported herein. A characteristic feature in P. brasiliensis is that the optical density of the cell wall increases at the site where budding begins and at the neck of the dividing cell, whereas B. dermatitidis does not undergo this alteration. The neck which is formed between the mother and daughter cell at the site of division is much wider in B. dermatitidis than in P. brasiliensis . The bud scar in P. brasiliensis appears as a truncated cone, the top of which is covered only by the inner layer of the cell wall; in comparison, in B. dermatitidis the bud scar exhibits a flattened surface covered by the cell wall. Both fungi show an increase in the number of mitochondria and infoldings of the cytoplasmic membrane at the site of separation, which indicates that at this site there is an increase of metabolic activity.

Protoplast formation by Histoplasma capsulatum yeasts using high concentrations of MgSO 4 occurs either by lysis of the bud or lysis of the entire cell wall. Both mechanisms may also occur simultaneously. Neither the protoplast emerging through a hole in the cell wall nor the freshly released protoplast has a recognizable cell wall or the remnant of such. The protoplast contains all the organelles of the normal cell except for mesosomes. During protoplast formation the nucleus increases in size and produces several nuclear masses by the invaginations of the internal layer of the nuclear membrane. All these nuclear masses are surrounded by the external layer of the nuclear membrane. Several nuclei with a normal nuclear membrane are formed later.

Kanetsuna, Fuminori (Instituto Venezolano de Investigaciones Cientificas, Caracas, Venezuela), and Luis M. Carbonell . Enzymes in glycolysis and the citric acid cycle in the yeast and mycelial forms of Paracoccidioides brasiliensis . J. Bacteriol. 92: 1315–1320. 1966.—Enzymatic activities in glycolysis, the hexose monophosphate shunt, and the citric acid cycle in cell-free extracts of the yeast and mycelial forms of Paracoccidioides brasiliensis were examined comparatively. Both forms have the enzymes of these pathways. Activities of glucose-6-phosphate dehydrogenase and malic dehydrogenase of the mycelial form were higher than those of the yeast form. Another 15 enzymatic activities of the mycelial form were lower than those of the yeast form. The activity of glyceraldehyde-3-phosphate dehydrogenase showed the most marked difference between the two forms, its activity in the mycelial form being about 20% of that in the yeast form.

The occurrence of a live hypha inside a dead yeast during the transformation from yeast to mycelium ofParacoccidioides brasiliensisis described.