Biochemical Studies on the Thermal Dimorphism of <i>Paracoccidioides brasiliensis</i>

Abstract

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 alpha-glucan, whereas the polysaccharides of the M-form cell wall were beta-glucan and galactomannan. The alpha-glucan of the Y form contained mainly alpha-(1 --> 3)-glycosidic linkage. The beta-glucan of the M form contained mainly beta-(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 alpha-glucan decreased rapidly after the temperature of the culture was changed from 37 to 20 C. The synthesis of beta-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 beta-glucanase activity than the Y form. From these results, a hypothesis for the production of the M form from the Y form is proposed.