Scanning Electron Microscopy of a True Cellulolytic Strain of Aureobasidium Grown on Crystalline Cellulose

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Abstract
This paper reports the presence of extracellular true cellulolytic activity in a brick-colored strain of Aureobasidium sp. isolated from soil of a sugar cane field of the State of Morelos, Mexico. Using scanning electron-microscopy (SEM), development of this strain on microcrystalline cellulose (a minimal medium) and potato-dextrose agar (PDA) was compared and related to its production of cellulases. On microcrystalline cellulose, on which other yeast-like fungi tested did not grow, our strain of Aureobasidium sp. grew well and showed good cellulolytic activity measured on filter paper, producing a maximum of 2.3 mg of reducing sugars ml/h-1. Swollen cells and spicules were rarely present and no blastospores were observed; chlamydospores and septa were the most conspicuous features. When grown on PDA, large numbers of blastospores were observed in the colony center but not at the periphery. The hyphae were well developed and covered with mucilaginous material; neither developing blastospores nor newly germinated blastospores had this material. No chlamydospores, swollen cells, or well-developed septa were observed on colonies grown on PDA. Our strain is morphologically similar to A. pullulans but differs from it because of its high, true cellulolytic activity on filter paper.