Differential Thermotolerance Adaptation between Species of Coccidioides.

Heather L Mead,Raquel Muñiz-Salazar,George R Thompson,Laura Rosio Castañón-Olivares,Paris S Hamm,Marc J Orbach,Christopher S Wendel,Paul Keim,Marcus De Melo Teixeira,Carmel Plude,Isaac N Shaffer,John N Galgiani,Nathan P Wiederhold,Bridget M Barker,Joel Terriquez

doi:10.3390/jof6040366

Abstract

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, was screened for mycelial growth rate at 37 °C and 28 °C on solid media. The radial growth rate was measured for 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 research.

Highlights

Coccidioidomycosis, or Valley fever, is an environmentally acquired disease caused by inhalation of arthroconidia of dimorphic fungi belonging to the genus Coccidioides
To define variability of one phenotypic trait between two Coccidioides species, we examined the ability of Coccidioides spp. to grow in filamentous form at 37 ◦ C and 28 ◦ C on Yeast Extract (YE) agar
Initial investigations occurred at the University of Arizona, and subsequent studies occurred at Northern Arizona University (Table 1)

Summary

Introduction

Coccidioidomycosis, or Valley fever, is an environmentally acquired disease caused by inhalation of arthroconidia of dimorphic fungi belonging to the genus Coccidioides. The fungi grow as filamentous mycelia, alternate cells of which autolyze and become fragile, leaving intact asexual arthroconidia that may disperse via wind or soil disruption. If inhaled by a susceptible host, an arthroconidium switches to a host-associated lifecycle and develops into a specialized infectious structure called a spherule. The host’s immune system either represses spherule replication or the host succumbs to the illness [1,2]. There are 146,000 new symptomatic U.S coccidioidal infections each year [4] the reported cases are substantially lower [5]

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Conclusion