Aureobasidium

Aureobasidium is a genus of melanized, yeast-like fungi in the phylum Ascomycota. Members are found worldwide in soils, on plant surfaces, wood, and indoor environments, often on leaves and fruit as epiphytes or saprophytes. The best studied species is Aureobasidium pullulans, which is notable for producing the extracellular polysaccharide pullulan.

Morphology and life cycle: Aureobasidium species are typically dimorphic, forming yeast-like cells and, under certain conditions, filamentous hyphae. Colonies are usually pigmented dark brown to black due to melanin, though some isolates appear light. Reproduction occurs by budding of yeast-like cells and by formation of spores in hyphal structures.

Ecology and applications: They are common on plant surfaces, wood, dust, and in damp indoor environments. A. pullulans is exploited commercially for pullulan production, which is used in food, pharmaceutical, and packaging applications. The genus has been investigated for biocontrol properties against plant pathogens and for its enzyme activities and pigment production.

Medical relevance: Aureobasidium species are generally environmental saprobes and only rarely cause human infection. In severely immunocompromised patients, A. pullulans and related species have been reported to contaminate blood cultures or cause localized infections such as keratitis or skin lesions. Identification relies on culture and molecular methods; treatment depends on antifungal susceptibility.

Taxonomy: Aureobasidium belongs to the Ascomycota and comprises several species, including A. pullulans, A. melanogenum, and A. nigricans. The taxonomy and species delineation have undergone revisions as molecular data accumulate.