Abstract
Candida species are a leading cause of opportunistic, hospital-associated bloodstream infections with high mortality rates, typically in immunocompromised patients. Several species, including Candida albicans, the most prevalent cause of infection, belong to the monophyletic CUG clade of yeasts. Innate immune cells such as macrophages are crucial for controlling infection, and C. albicans responds to phagocytosis by a coordinated induction of pathways involved in catabolism of nonglucose carbon sources, termed alternative carbon metabolism, which together are essential for virulence. However, the interactions of other CUG clade species with macrophages have not been characterized. Here, we analyzed transcriptional responses to macrophage phagocytosis by six Candida species across a range of virulence and clinical importance. We define a core induced response common to pathogenic and nonpathogenic species alike, heavily weighted to alternative carbon metabolism. One prominent pathogen, Candida parapsilosis, showed species-specific expansion of phagocytosis-responsive genes, particularly metabolite transporters. C. albicans and Candida tropicalis, the other prominent pathogens, also had species-specific responses, but these were largely comprised of functionally uncharacterized genes. Transcriptional analysis of macrophages also demonstrated highly correlated proinflammatory transcriptional responses to different Candida species that were largely independent of fungal viability, suggesting that this response is driven by recognition of conserved cell wall components. This study significantly broadens our understanding of host interactions in CUG clade species, demonstrating that although metabolic plasticity is crucial for virulence in Candida, it alone is not sufficient to confer pathogenicity. Instead, we identify sets of mostly uncharacterized genes that may explain the evolution of pathogenicity. IMPORTANCE Candidiasis is a major fungal infection by Candida species, causing life-threatening invasive disease in immunocompromised patients. C. albicans, which is adapted to commensalism of human mucosae, is the most common cause. While several other species cause infection, most are less prevalent or less virulent. As innate immune cells are the primary defense against Candida infection, we compared the transcriptional responses of C. albicans and related species to phagocytosis by macrophages, to understand the basis of variation in pathogenesis. This response, including the metabolic remodeling required for virulence in C. albicans, was strikingly conserved across the virulence spectrum. Macrophage responses to different species were also highly similar. This study indicates that important elements of host-pathogen interactions in C. albicans are not driven by adaptation to the mammalian host and improves our understanding of pathogenicity in opportunistic fungal species that are understudied but collectively impose a significant threat of their own.