Aureobasidium pullulans (Pullaria)

[ Aureobasidium pullulans and the Environment ] [ Suggested Reading ]

This yeast-like fungus is commonly found on caulk or damp window frames in bathrooms. Aureobasidium (Pullularia) may be pink or black in color. Although it seldom causes infections, it can be allergenic. This is one type of mold that is a type of mildew. It will grow in cooler climates and along with Cladosporium is commonly found growing on siding. Pullularia occurs indoors in areas of free water, such as condensate pans, or as a primary colonist of broadloom following a flood. Because its growth form is yeast-like (and are not forcibly discharged), its cells/spores only become airborne through mechanical disruption of contaminated materials or aspiration of contaminated water.

Aureobasidium pullulans is not a primary human pathogen nor is it recognized as a producer of significant mycotoxins. High airborne levels of this fungus have been associated with allergic complaints probably due to respiratory irritation mediated by cell-wall components (e. g. beta glucans, glycoproteins), it has also been known as an irritant, and to cause pulmonary problems (small airway).

Aureobasidium pullulans and the Environment

Polyhydroxy compounds from Aureobasidium pullulans exposed to stress treatments of heat, salt, and simultaneous heat and salt were isolated, identified, and quantified. Results from both thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC) showed that concentrations of trehalose, mannitol, and glycerol increased under stress conditions that induce osmotic- and thermotolerance in A. pullulans. The cellular concentration of trehalose increased in heat-stressed and in simultaneously heat- and salt-stressed cells but not in cells subjected to salt stress alone. Mannitol increased under all stress conditions examined, while an increase in intracellular glycerol was apparent only in salt-stressed cells. The significance of these findings in relation to stress tolerance in salt marsh environments is discussed.

When A. pullulans cells grown at 25 C for 40 h were exposed to sublethal stress conditions (35 C, 4. 5% NaCl, or concurrent treatments of both), the intracellular levels of certain polyhyroxy compounds increased compared to the controls as shown by both TLC and HPLC. Thin-layer chromatograms of cell extracts that were heat shocked at 35 C for 45 min showed a marked increase in trehalose levels compared with controls (data not shown). This represented a near doubling of the mean cell concentration of trehalose compared with untreated controls ( ) as determined by HPLC (compare the results for control cells in  with those for heat-shocked cells in).

Although changes in mannitol were not obvious by TLC analysis (due to the overlapping migration of glucose and mannitol and perhaps other sugars in the extracts) HPLC clearly showed a nearly two-fold increase in mannitol as a result of heat shock (). The low level of glycerol in untreated cells did not increase in heat-shocked cells ( ) and glycerol was not detected by TLC. The peak with a retention time of approximately 5 min that appeared in all the HPLC chromatograms appears to be a product of the polysaccharide pullulan which is produced by this fungus. The pullulan "halos" that form around cell pellets during centrifugation produce peaks with a retention time of approximately 5 min when subjected to HPLC.

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Suggested Reading / Abstract

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