PT  - JOURNAL ARTICLE
AU  - Heather L. Mead
AU  - Paris S. Hamm
AU  - Isaac N. Shaffer
AU  - Marcus de Melo Teixeira
AU  - Christopher S. Wendel
AU  - Nathan P. Wiederhold
AU  - George R. Thompson III
AU  - Raquel Muñiz-Salazar
AU  - Laura Rosio Castañón-Olivares
AU  - Paul Keim
AU  - Carmel Plude
AU  - Joel Terriquez
AU  - John N. Galgiani
AU  - Marc J. Orbach
AU  - Bridget M. Barker
TI  - Differential thermotolerance adaptation between species of <em>Coccidioides</em>
AID  - 10.1101/2020.08.12.247635
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 2020.08.12.247635
4099  - http://biorxiv.org/content/early/2020/10/16/2020.08.12.247635.short
4100  - http://biorxiv.org/content/early/2020/10/16/2020.08.12.247635.full
AB  - Coccidioidomycosis, or Valley fever, is caused by two species of dimorphic fungi. Based on molecular phylogenetic evidence, the genus Coccidioides contains two reciprocally monophyletic species: C. immitis and C. posadasii. However, phenotypic variation between species has not been deeply investigated. We therefore explored differences in growth rate under various conditions. A collection of 39 C. posadasii and 46 C. immitis isolates, representing the full geographical range of the two species, were screened for mycelial growth rate at 37°C and 28°C on solid media. The radial growth rate was measured over 16 days on yeast extract agar. A linear mixed effect model was used to compare the growth rate of C. posadasii and C. immitis at 37°C and 28°C respectively. C. posadasii grew significantly faster at 37°C, when compared to C. immitis; whereas both species had similar growth rates at 28°C. These results indicate thermotolerance differs between these two species. As the ecological niche has not been well-described for Coccidioides spp., and disease variability between species has not been shown, the evolutionary pressure underlying the adaptation is unclear. However, this research reveals the first significant phenotypic difference between the two species that directly applies to ecological and clinical research.Competing Interest StatementThe authors have declared no competing interest.