Patterns of substrate utilization in species of Capronia and allied black yeasts: ecological and taxonomic implications

Abstract

Forty-one isolates representing 14 members of the ascomycete genus Capronia and 15 black yeasts belonging to the anamorph genera Exophiala, Cladosporium, Ramichloridium and Rhinocladiella were tested for their ability to degrade amylose, casamino acids, casein, cellulose, chitin, gelatin, lignin, lipid, pectin and urea. The results of these tests were compared to assays for the breakdown of the same compounds by eight ascomycetes, basidiomycetes and zygomycetes that served as reference strains. Species of Capronia and black yeasts were unable to degrade amylose, cellulose, chitin, lignin and pectin. The utilization of casein, casamino acids, lipid, gelatin and urea varied among the taxa tested. These results indicate that plant-derived polymers and chitin are inaccessible to the Herpotrichiellaceae in natural systems and support the hypothesis that the members of this family are saprobes of secondary or higher incidence (hypersaprobes). Clinical and nonclinical Herpotrichiellaceae could not be discriminated on the basis of their enzymatic capabilities. Of the 12 substrate utilization tests employed in this study, only those used to assess the hydrolysis of casamino acids, casein and lipid proved valuable for distinguishing members of the genera Capronia, Exophiala and Ramichloridium. A simple method for detecting chitinolytic activity in fungi using chitin azure is described.

Key Words:

• chitin
• ecology
• enzyme
• Exophiala
• Herpotrichiellaceae
• nutrition
• taxonomy