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Identify putative volatile biomarkers of Coccidioides spp. grown in vitro

ABSTRACT: Valley fever (coccidioidomycosis) is an endemic fungal pneumonia of the North and South American deserts. The causative agents of Valley fever are the dimorphic fungi Coccidioides immitis and C. posadasii, which grow as mycelia in the environment and spherules within the lungs of vulnerable hosts. The current diagnostics for Valley fever are severely lacking due to poor sensitivity and invasiveness, contributing to a 23-day median time-to-diagnosis, and therefore new diagnostic tools are needed. We are working toward the development of a breath-based diagnostic for coccidioidomycosis, and in this initial study we characterized the volatile metabolomes (or volatilomes) of in vitro cultures of Coccidioides. Using solid-phase microextraction and comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC–TOFMS), we characterized the VOCs produced by six strains of each species during mycelial or spherule growth. We detected a total of 353 VOCs that were at least two-fold more abundant in a Coccidioides culture versus medium controls and found the volatile metabolome of Coccidioides is more dependent on growth phase (spherule versus mycelia) than on the species. The volatile profiles of C. immitis and C. posadasii have strong similarities, indicating that a single suite of Valley fever breath biomarkers can be developed to detect both species.

ORGANISM(S): Fungi Coccidioides Posadasii;coccidioides Immitis Coccidioides Posadasii

TISSUE(S): Fungal Cells

DISEASE(S): Valley Fever

SUBMITTER: Heather Bean

PROVIDER: ST001659 | MetabolomicsWorkbench | Fri Jan 22 00:00:00 GMT 2021

REPOSITORIES: MetabolomicsWorkbench

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Project description:The oomycete P. oligandrum is a soil-inhabiting parasite and predator of both fungi and oomycetes and uses hydrolytic enzymes extensively to penetrate and hydrolyze its host or prey. Other mechanisms have been overlooked, and we investigated whether P. oligandrum-produced volatile organic compounds (VOCs) could also be contributing to antagonism. VOCs have diverse functions, including contributing to antagonism in ecological interactions and potential applications in biocontrol. The growth-inhibiting activity of P. oligandrum VOCs was tested on P. myriotylum – a host or prey of P. oligandrum – coupled with electron microscopy, biochemical assays and transcriptomic analysis. The total VOCs produced by P. oligandrum reduced P. myriotylum growth by 80% and zoospore levels by 60%. GC-MS identified twenty-three VOCs, and methyl heptenone, D-limonene, 2-undecanone and 1-octanal were potent inhibitors of P. myriotylum growth and led to increased production of reactive oxygen species at a concentration that did not inhibit P. oligandrum growth. Exposure to the total VOCs of P. oligandrum led to shrinkage of P. myriotylum hyphae, and lysis of the cellular membranes and organelles. Transcriptomic analysis of P. myriotylum exposed to the P. oligandrum VOCs at increasing levels of growth inhibition showed initially a strong upregulation of putative detoxification related genes that was not maintained later during exposure to the VOCs. The inhibition of P. myriotylum growth continued after the exposure to the VOCs was discontinued and led to reduced leaf lesion size during P. myriotylum infection of its plant host. The VOCs produced by P. oligandrum could be another factor alongside hydrolytic enzymes contributing to its ecological role as a microbial antagonist where the concentration of the VOCs may be inhibitory in particular ecological niches such as in soil. The VOCs analyzed here may also be contributing to the biocontrol of diseases using P. oligandrum commercial preparations.

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Identify putative volatile biomarkers of Coccidioides spp. grown in vitro

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