Trauma-related necrotizing myocutaneous
mucormycosis (NMM) has a high morbidity and mortality in victims of combat-related
injuries, geometeorological disasters, and severe
burns. Inspired by the observation that several recent clusters of NMM have been associated with extreme mechanical forces (e.g., during tornados), we studied the impact of mechanical stress on Mucoralean biology and virulence in a Drosophila melanogaster
infection model. In contrast to other experimental procedures to exert mechanical stress, tornadic shear challenge (
TSC) by magnetic stirring induced a hypervirulent phenotype in several clinically relevant Mucorales species but not in Aspergillus or Fusarium Whereas fungal growth rates, morphogenesis, and susceptibility to noxious environments or phagocytes were not altered by
TSC, soluble factors released in the supernatant of shear-challenged R. arrhizus spores rendered static spores hypervirulent. Consistent with a rapid decay of
TSC-induced hypervirulence, minimal transcriptional changes were revealed by comparative
RNA sequencing analysis of static and shear-challenged Rhizopus arrhizus However, inhibition of the
calcineurin/
heat shock protein 90 (hsp90) stress response circuitry by
cyclosporine and
tanespimycin abrogated the increased pathogenicity of R. arrhizus spores following
TSC. Similarly,
calcineurin loss-of-function mutants of Mucor circinelloides displayed no increased virulence capacity in flies after undergoing
TSC. Collectively, these results establish that
TSC induces hypervirulence specifically in Mucorales and point out the
calcineurin/hsp90 pathway as a key orchestrator of this phenotype. Our findings invite future studies of topical
calcineurin inhibitor treatment of
wounds as an adjunct mitigation strategy for NMM following high-energy
trauma.IMPORTANCE Given the limited efficacy of current medical treatments in
trauma-related necrotizing
mucormycosis, there is a dire need to better understand the Mucoralean pathophysiology in order to develop novel strategies to counteract fungal tissue invasion following severe
trauma. Here, we describe that tornadic shear stress challenge transiently induces a hypervirulent phenotype in various pathogenic Mucorales species but not in other molds known to cause
wound infections. Pharmacological and genetic inhibition of
calcineurin signaling abrogated hypervirulence in shear stress-challenged Mucorales, encouraging further evaluation of (topical)
calcineurin inhibitors to improve therapeutic outcomes of NMM after combat-related
blast injuries or violent storms.