Aureobasidium pullulans
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Aureobasidium pullulans is a ubiquitous yeast-like fungus that can be found in different environments (e.g. soil, water, air and limestone). It is well known as a naturally occurring epiphyte or endophyte of a wide range of plant species (e.g. apple, grape, cucumber, green beans, cabbage) without causing any symptoms of disease. A. pullulans has a high importance in biotechnology for the production of different enzymes, siderophores and pullulan. Furthermore A. pullulans is used in biological control of plant diseases, especially storage diseases. In addition to the beneficial aspects, A. pullulans is in a few cases associated with plant disease (e.g. stigmatomycosis on cotton). It can be cultivated on potato dextrose agar, where it produces smooth, faint pink, yeast-like colonies covered with a slimy mass of spores. Older colonies change to black due to chlamydospore production. Primary conidia are hyaline, smooth, ellipsoidal, one-celled, and variable in shape and size; secondary conidia are smaller. Conidiophores are undifferentiated, intercalary or terminal, or arising as short lateral branches. Endoconidia are produced in an intercalary cell and released into a neighboring empty cell. Hyphae are hyaline, smooth, and thinwalled, with transverse septa. The fungus grows at 10–35°C with optimum growth at 30°C.
Chronic human exposure via humidifiers or air conditioners can lead to hypersensitivity pneumonitis (extrinsic allergic alveolitis) or "humidifier lung". This condition is characterized acutely by dyspnea, cough, fever, chest infiltrates, and acute inflammatory reaction. The condition can also be chronic, and lymphocyte-mediated. The chronic condition is characterized radiographically by reticulonodular infiltrates in the lung, with apical sparing.
A. pullulans is notable for its phenotypic plasticity. Colony morphology may be affected by carbon source, colony age, temperature, light and substrate, with colonies ranging from homogeneous to sectored, yeast-like to filamentous growth, and from small to large. These changes, potentially influenced by epigenetic factors, and the particular developmental sequences that the colonies proceed through may be observed with the naked eye.