Abstract
Candida spp. yeast-like fungi are opportunistic pathogens in humans and have been recently found to release extracellular vesicles (EVs) that are involved in many vital biological processes in fungal cells. These include communication between microorganisms and host–pathogen interactions during infection. The production of EVs and their content have been significantly characterized in the most common candidal species Candida albicans, including the identification of numerous virulence factors and cytoplasmic proteins in the EV cargo. We have here conducted the isolation and proteomic characterization of EVs produced by the clinically important non-albicans Candida species C. glabrata, C. tropicalis and C. parapsilosis. With the use of ultracentrifugation of the cell-free culture supernatant, the candidal EVs were collected and found to be a heterogeneous population of particles for each species with sizes ranging from 60–280 nm. The proteinaceous contents of these vesicles were analyzed using LC-MS/MS, with particular attention paid to surface-expressed proteins that would come into immediate and direct contact with host cells. We thereby identified 42 extracellular and surface-connected proteins from C. glabrata, 33 from C. parapsilosis, and 34 from C. tropicalis, including membrane-associated transporters, glycoproteins and enzymes involved in the organization of the fungal cell wall, as well as several cytoplasmic proteins, including alcohol dehydrogenase, enolase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase and pyruvate kinase, for which the vesicular transport is a possible mechanism underlying their non-classical secretion.
Highlights
Polymorphous fungi of the Candida genus are still considered to be the main fungal infectious agents in humans, causing invasive mycoses and bloodstream infections that threaten the health and life of diverse groups of vulnerable patients
The aim of our present study was the isolation and characterization of extracellular vesicles (EVs) produced by C. glabrata, C. tropicalis and C. parapsilosis, with a particular focus on proteomic analysis and the proteins exposed at the surface of EVs that come into immediate and direct contact with host cells
For C. glabrata, the particle number was determined as 2.55 ± 0.17 × 1010 of produced EVs, whereas for C. parapsilosis this was 2.3 ± 0.08 × 1010 particles and for C. tropicalis was 8.88 ± 0.63 × 109 particles
Summary
Polymorphous fungi of the Candida genus are still considered to be the main fungal infectious agents in humans, causing invasive mycoses and bloodstream infections that threaten the health and life of diverse groups of vulnerable patients. Groups that are susceptible to poor outcomes from these infections include infants, the elderly, and individuals with impaired immunity or weakened defense mechanisms due to systemic diseases such as diabetes or cancer, or who have had medical procedures such as surgery or the application of parenteral nutrition or central venous catheters [1,2]. The best-known and the most common species of this genus causing infections in humans is still C. albicans, the global epidemiology of candidiasis is currently changing and other species, collectively called non-albicans Candida (NAC) species and primarily including C. glabrata, C. parapsilosis and C. tropicalis, are increasingly emerging as etiological agents of systemic diseases [8,9,10]. The biology and the virulence mechanisms of NAC species are still not thoroughly understood, which is a important and pressing issue if one takes into account the growing clinical significance of these fungi and the increasing number of serious infections they cause [1]
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