Systematic phenotyping of a large-scale Candida glabrata deletion collection reveals novel antifungal tolerance genes.

Tobias Schwarzmüller,Sascha Brunke,Ilse D Jacobsen,Ken Haynes,Dominique Ferrandon,Walter Glaser,Arnaud Firon,Jessica Quintin,Katja Seider,Biao Ma,Murielle Chauvel,Karl Kuchler,Fabian Istel,Steffen Rupp,Michael Tscherner,Toni Gabaldón,Ute Zeidler,Lauren Ames,Helmut Jungwirth,Bernhard Hube,Ekkehard Hiller,Brian Green,Vitor Cabral,Ingrid E Frohner ,Marina Marcet‐Houben ,Sophie Bachellier‐Bassi ,Christophe D’enfert ,Brendan P Cormack

doi:10.1371/journal.ppat.1004211

Abstract

The opportunistic fungal pathogen Candida glabrata is a frequent cause of candidiasis, causing infections ranging from superficial to life-threatening disseminated disease. The inherent tolerance of C. glabrata to azole drugs makes this pathogen a serious clinical threat. To identify novel genes implicated in antifungal drug tolerance, we have constructed a large-scale C. glabrata deletion library consisting of 619 unique, individually bar-coded mutant strains, each lacking one specific gene, all together representing almost 12% of the genome. Functional analysis of this library in a series of phenotypic and fitness assays identified numerous genes required for growth of C. glabrata under normal or specific stress conditions, as well as a number of novel genes involved in tolerance to clinically important antifungal drugs such as azoles and echinocandins. We identified 38 deletion strains displaying strongly increased susceptibility to caspofungin, 28 of which encoding proteins that have not previously been linked to echinocandin tolerance. Our results demonstrate the potential of the C. glabrata mutant collection as a valuable resource in functional genomics studies of this important fungal pathogen of humans, and to facilitate the identification of putative novel antifungal drug target and virulence genes.

Highlights

Candida glabrata, a small, asexual, haploid yeast, is the second most frequent cause of candidiasis after Candida albicans, accounting for approximately 15%–25% of clinical cases [1,2,3,4]
Clinical infections by the yeast-like pathogen Candida glabrata have been ever-increasing over the past years
Extensive profiling of phenotypes reveals a number of novel genes implicated in tolerance to antifungal drugs that interfere with proper cell wall function, as well as genes affecting fitness of C. glabrata both during normal growth and under environmental stress

Summary

Introduction

A small, asexual, haploid yeast, is the second most frequent cause of candidiasis after Candida albicans, accounting for approximately 15%–25% of clinical cases [1,2,3,4]. C. glabrata forms part of the normal microbial flora in humans, but can cause serious infections in immunocompromised and hospitalized patients; antibiotic exposure and presence of central venous catheter devices, being additional important risk factors for disease development [2]. In contrast to the pleomorphic diploid C. albicans [5], C. glabrata is found clinically, exclusively as monomorphic yeast cells. It lacks several attributes considered key mediators of fungal pathogenicity in other Candida spp, such as secretion of proteases and lipases [6,7]. Despite the apparent absence of these well-known fungal virulence traits, C. glabrata remains highly pathogenic to humans. C. glabrata may rely upon distinct strategies and other virulence attributes to initiate infection, as well as to persist in infected patients

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Conclusion