Hydrolytic enzymes in Paracoccidioides brasiliensis--ecological aspects

Paracoccidioides brasiliensis is a thermally dimorphic fungus that causes paracoccidioidomycosis. The yeast form of this pathogen is found in the animal host whereas the mycelial form is recovered from living and non-living organic material. The sole carbon source available in these habitats is represented by polysaccharides from the plant cell wall. Hydrolytic enzymes are necessary to convert these polymers into simple sugars for fungal metabolism. We report on the presence of ortholog genes of hydrolytic enzymes identified in the P. brasiliensis transcriptome and on hydrolytic activities in supernatants of induced P. brasiliensis cultures of mycelium and yeast cells. Enzymatic assays have shown cellulase and xylanase activities, both being higher in mycelium than in the yeast form. Amylase and chitinase activities were detected only in mycelium. Data so far reinforce the idea that mycelial P. brasiliensis is a saprobe.

General metabolism of the dimorphic and pathogenic fungus Paracoccidioides brasiliensis

Annotation of the transcriptome of the dimorphic fungus Paracoccidioides brasiliensis has set the grounds for a global understanding of its metabolism in both mycelium and yeast forms. This fungus is able to use the main carbohydrate sources, including starch, and it can store reduced carbons in the form of glycogen and trehalose; these provide energy reserves that are relevant for metabolic adaptation, protection against stress and infectivity mechanisms. The glyoxylate cycle, which is also involved in pathogenicity, is present in this fungus. Classical pathways of lipid biosynthesis and degradation, including those of ketone body and sterol production, are well represented in the database of P. brasiliensis. It is able to synthesize de novo all nucleotides and amino acids, with the sole exception of asparagine, which was confirmed by the fungus growth in minimal medium. Sulfur metabolism, as well as the accessory synthetic pathways of vitamins and co-factors, are likely to exist in this fungus.