Morphogenetic Effect of L-cysteine on Pseudogymnoascus destructans and Related Species

Abstract

The addition of L-cysteine to culture media is shown to cause a morphogenetic effect on Pseudogymnoascus (Geomyces) destructans, the causal agent of bat white-nose syndrome, and on several North American Pseudogymnoascus species in vitro. Under elevated levels of L-cysteine, seven P. destructans isolates from various geographical localities produced yeast-like cells on amended Sabouraud’s dextrose agar within 30 days at 7–10 °C. The yeast-like cells appear in semisolid, black, pigmented masses composed of ellipsoidal to obtuse cells that average 13 × 5.5 µm and demonstrate blastic development easily differentiating them from the typical curved conidia which average 6 × 3 µm. The yeast-like cells were shown to revert to filamentous form when cultured on non-amended Sabouraud’s dextrose agar. No yeast-like cells were visualized in four other isolates within the Pseudogymnoascus roseus complex or in two additional, distantly-related Pseudogymnoascus isolates when exposed to the same elevated levels of L-cysteine. The sensitivity of P. destructans to L-cysteine is believed to be a response to the reduced oxidation-reduction potential of the amended medium, but further research is needed to understand the biochemical mechanisms.