Abstract
Candida albicans and Candida dubliniensis are pathogenic fungi that are highly related but differ in virulence and in some phenotypic traits. During in vitro growth on certain nutrient-poor media, C. albicans and C. dubliniensis are the only yeast species which are able to produce chlamydospores, large thick-walled cells of unknown function. Interestingly, only C. dubliniensis forms pseudohyphae with abundant chlamydospores when grown on Staib medium, while C. albicans grows exclusively as a budding yeast. In order to further our understanding of chlamydospore development and assembly, we compared the global transcriptional profile of both species during growth in liquid Staib medium by RNA sequencing. We also included a C. albicans mutant in our study which lacks the morphogenetic transcriptional repressor Nrg1. This strain, which is characterized by its constitutive pseudohyphal growth, specifically produces masses of chlamydospores in Staib medium, similar to C. dubliniensis. This comparative approach identified a set of putatively chlamydospore-related genes. Two of the homologous C. albicans and C. dubliniensis genes (CSP1 and CSP2) which were most strongly upregulated during chlamydospore development were analysed in more detail. By use of the green fluorescent protein as a reporter, the encoded putative cell wall related proteins were found to exclusively localize to C. albicans and C. dubliniensis chlamydospores. Our findings uncover the first chlamydospore specific markers in Candida species and provide novel insights in the complex morphogenetic development of these important fungal pathogens.
Highlights
The pathogenic yeast Candida albicans represents the clinically most important member of the genus Candida [1]
We found an incubation for 28 h at 25uC optimal for chlamydospore analysis in Staib liquid medium. Both the C. dubliniensis wild type as well as the C. albicans nrg1D mutant exclusively grew in form of pseudohyphae, almost all of which produced chlamydospores at their terminal ends (Figure 1)
The formation of chlamydospores by C. albicans nrg1D pseudohyphae is induced in Staib medium, allowing the identification of putative chlamydospore related genes by comparative gene expression analysis
Summary
The pathogenic yeast Candida albicans represents the clinically most important member of the genus Candida [1]. C. albicans has been differentiated for a long time from other yeast-like fungi by a species-specific, morphogenetic characteristic, i.e. the formation of chlamydospores. These large, thick-walled, spherical cells are produced by C. albicans on specific nutrient-poor media such as rice-extract or corn meal agar at room temperature, typically from suspensor cells at the end of pseudohyphae [2,3,4,5,6]. The question remains why have these species retained the capacity to produce these complex and unusual structures and what exactly is their purpose in the Candida life cycle?
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