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Mold of the month May: Purpureocillium lilacinum
13.6.2022

Mold of the month June: Purpureocillium lilacinum

Molecular studies resulted in a new taxonomic classification of Purpureocillium lilacinum into a separate genus (Luangsa-ard et al. 2011). In older literature, this mold is occasionally still described as Paecilomyces lilacinum or also Penicillium lilacinum (Domsch et al. 2007 Sec. Ed.).

Detailed measurements of water demand (aW value) are not known (Mold Guide from the German Federal Environmental Agency 2017), but since most of the findings of this globally distributed species are from water-associated substrates (Food and Indoor Fungi Sec. Ed. 2019), it can be assumed that elevated detection of Purpureocillium lilacinum indoors may indicate increased humidity.

The species often occurs in biofilms with other molds and bacteria, which can make it comparatively resistant to chemical disinfectants.

Picture: Spore carrier of Purpureocillium lilacinum at 400x magnification under light microscope. Phialides with elongated bottle neck in typical clusters of 2 - 4 phialides per metulae. Spores in long chains roundish with tapering ends (in the picture no longer on the phialides -> preparation artifact). Spore carrier elongated with septa and poorly colored base (little blue). Preparation stained with cotton blue.

Purpureocillium lilacinum is used economically as a biological control agent against certain nematodes (threadworms) and insects. Thermotolerant strains can grow at temperatures as low as 38°C and thus can cause infections in humans in very rare cases (Atlas of Clinical Fungi 4th Ed. 2020).

In the environment, Purpureocillium lilacinum likely occurs as a decomposer of dead organic material and does not appear to differentiate between plant or animal remains (Food and Indoor Fungi Sec. Ed. 2019).

Purpureocillium lilacinum from pure culture

Purpureocillium lilacinum from pure culture

Shown on the left: Incubated for seven days at 25 °C on MEA agar. Three colonies with the characteristic purple coloration. Some with white aerial mycelium in the center of the colonies.
Shown on the right: Incubated for seven days at 25 °C on DG18 agar. Two colonies with whitish-gray margins and slightly purple colored center (light brown tint present in some cases). Colonies grow significantly slower under the osmotic stress of DG18 agar (compared to MEA agar).

6100x magnification under the SEM

6100x magnification under the SEM

Spore carriers around mycelium of Purpureocillium lilacinum sputtered with gold under vacuum at 6100x magnification under scanning electron microscope (SEM). Spore carriers with phialides and spore chains starting from mycelium. Spore carriers occurring in bundles (Penicillium-like) and single (Acremonium-like). Dents in the spores and spore carriers correspond to preparation artifacts caused by vacuum sputtering.

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