Disruption of the Transcriptional Regulator Cas5 Results in Enhanced Killing of Candida albicans by Fluconazole

ABSTRACTAzole antifungal agents such as fluconazole exhibit fungistatic activity againstCandida albicans. Strategies to enhance azole antifungal activity would be therapeutically appealing. In an effort to identify transcriptional pathways that influence the killing activity of fluconazole, we sought to identify transcription factors (TFs) involved in this process. From a collection ofC. albicansstrains disrupted for genes encoding TFs (O. R. Homann, J. Dea, S. M. Noble, and A. D. Johnson, PLoS Genet. 5:e1000783, 2009,http://dx.doi.org/10.1371/journal.pgen.1000783), four strains exhibited marked reductions in minimum fungicidal concentration (MFCs) in both RPMI and yeast extract-peptone-dextrose (YPD) media. One of these genes,UPC2, was previously characterized with regard to its role in azole susceptibility. Of mutants representing the three remaining TF genes of interest, one (CAS5) was unable to recover from fluconazole exposure at concentrations as low as 2 μg/ml after 72 h in YPD medium. This mutant also showed reduced susceptibility and a clear zone of inhibition by Etest, was unable to grow on solid medium containing 10 μg/ml fluconazole, and exhibited increased susceptibility by time-kill analysis.CAS5disruption in highly azole-resistant clinical isolates exhibiting multiple resistance mechanisms did not alter susceptibility. However,CAS5disruption in strains with specific resistance mutations resulted in moderate reductions in MICs and MFCs. Genome-wide transcriptional analysis was performed in the presence of fluconazole and was consistent with the suggested role ofCAS5in cell wall organization while also suggesting a role in iron transport and homeostasis. These findings suggest that Cas5 regulates a transcriptional network that influences the response ofC. albicansto fluconazole. Further delineation of this transcriptional network may identify targets for potential cotherapeutic strategies to enhance the activity of the azole class of antifungals.

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Paradoxical Effect of Caspofungin: Reduced Activity against Candida albicans at High Drug Concentrations

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.48.9.3407-3411.2004 ◽

2004 ◽

Vol 48 (9) ◽

pp. 3407-3411 ◽

Cited By ~ 167

Author(s):

David A. Stevens ◽

Marife Espiritu ◽

Rachana Parmar

Keyword(s):

Candida Albicans ◽

Resistance Mechanisms ◽

Paradoxical Effect ◽

Fungal Cell ◽

High Drug ◽

Minimum Fungicidal Concentration ◽

Drug Concentrations ◽

High Concentrations ◽

Glucan Synthesis

ABSTRACT Resistance problems with caspofungin, an echinocandin inhibitor of fungal cell wall glucan synthesis, have been rare. We noted paradoxical turbid growth of Candida albicans isolates in broth in some high (supra-MIC) concentrations. Among isolates submitted for susceptibility testing and screened at drug concentrations up to 12.5 μg/ml, the frequency was 16%. Analysis of the turbid growth indicated slowing of growth in the presence of drug but with numbers of CFU up to 72% those of drug-free controls. Clearing of growth again by the highest drug concentrations produced a quadriphasic pattern in a tube dilution series. Cells growing at high drug concentrations were not resistant on retesting but showed the paradoxical effect of the parent. Among a selected series of isolates tested at concentrations up to 50 μg/ml, an additional 53% showed a “mini-paradoxical effect”: no turbid growth but incomplete killing at high concentrations (supra-minimum fungicidal concentration). These effects were reproducible; medium dependent in extent; noted in macro- and microdilution, in the presence or absence of serum, and on agar containing drug (but not when drug concentrations were not constant, as in agar diffusion); not seen with other echinocandins and less commonly in other Candida species; and not due to destruction of drug in tubes showing the effect. Cooperative enhancement of inhibition by a second drug could eradicate the effect. We postulate that high drug concentrations derepress or activate resistance mechanisms. The abilities of subpopulations to survive at high drug concentrations could have in vivo consequences.

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Novel Genes Related to Ceftriaxone Resistance Found among Ceftriaxone-Resistant Neisseria gonorrhoeae Strains SelectedIn Vitro

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00149-15 ◽

2016 ◽

Vol 60 (4) ◽

pp. 2043-2051 ◽

Cited By ~ 15

Author(s):

Zijian Gong ◽

Wei Lai ◽

Min Liu ◽

Zhengshuang Hua ◽

Yayin Sun ◽

...

Keyword(s):

Neisseria Gonorrhoeae ◽

Resistance Mechanisms ◽

Health Concern ◽

Cross Resistance ◽

Growth Time ◽

Single Mutation ◽

Global Public Health ◽

Differential Analysis ◽

Content Type ◽

Genes Encoding

ABSTRACTThe emergence of ceftriaxone-resistantNeisseria gonorrhoeaeis currently a global public health concern. However, the mechanism of ceftriaxone resistance is not yet fully understood. To investigate the potential genes related to ceftriaxone resistance inNeisseria gonorrhoeae, we subcultured six gonococcal strains with increasing concentrations of ceftriaxone and isolated the strains that became resistant. After analyzing several frequently reported genes involved in ceftriaxone resistance, we found only a single mutation inpenA(A501V). However, differential analysis of the genomes and transcriptomes between pre- and postselection strains revealed many other mutated genes as well as up- and downregulated genes. Transformation of the mutatedpenAgene into nonresistant strains increased the MIC between 2.0- and 5.3-fold, and transformation of mutatedftsXincreased the MIC between 3.3- and 13.3-fold. Genes encoding the ABC transporters FarB, Tfq, Hfq, and ExbB were overexpressed, whilepilM,pilN, andpilQwere downregulated. Furthermore, the resistant strain developed cross-resistance to penicillin and cefuroxime, had an increased biochemical metabolic rate, and presented fitness defects such as prolonged growth time and downregulated PilMNQ. In conclusion, antimicrobial pressure could result in the emergence of ceftriaxone resistance, and the evolution of resistance ofNeisseria gonorrhoeaeto ceftriaxone is a complicated process at both the pretranscriptional and posttranscriptional levels, involving several resistance mechanisms of increased efflux and decreased entry.

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Involvement of PatE, a Prophage-Encoded AraC-Like Regulator, in the Transcriptional Activation of Acid Resistance Pathways of Enterohemorrhagic Escherichia coli Strain EDL933

Applied and Environmental Microbiology ◽

10.1128/aem.00617-12 ◽

2012 ◽

Vol 78 (15) ◽

pp. 5083-5092 ◽

Cited By ~ 7

Author(s):

Jennifer K. Bender ◽

Judyta Praszkier ◽

Matthew J. Wakefield ◽

Kathryn Holt ◽

Marija Tauschek ◽

...

Keyword(s):

Escherichia Coli ◽

Transcriptional Activation ◽

Regulatory Protein ◽

Acid Resistance ◽

Enterohemorrhagic Escherichia Coli ◽

Transcriptional Analysis ◽

Mobility Shift ◽

Content Type ◽

Infectious Dose ◽

Genes Encoding

ABSTRACTEnterohemorrhagicEscherichia coli(EHEC) O157:H7 is a lethal human intestinal pathogen that causes hemorrhagic colitis and the hemolytic-uremic syndrome. EHEC is transmitted by the fecal-oral route and has a lower infectious dose than most other enteric bacterial pathogens in that fewer than 100 CFU are able to cause disease. This low infectious dose has been attributed to the ability of EHEC to survive in the acidic environment of the human stomach.In silicoanalysis of the genome of EHEC O157:H7 strain EDL933 revealed a gene,patE, for a putative AraC-like regulatory protein within the prophage island, CP-933H. Transcriptional analysis inE. colishowed that the expression ofpatEis induced during stationary phase. Data from microarray assays demonstrated that PatE activates the transcription of genes encoding proteins of acid resistance pathways. In addition, PatE downregulated the expression of a number of genes encoding heat shock proteins and the type III secretion pathway of EDL933. Transcriptional analysis and electrophoretic mobility shift assays suggested that PatE also activates the transcription of the gene for the acid stress chaperonehdeAby binding to its promoter region. Finally, assays of acid tolerance showed that increasing the expression of PatE in EHEC greatly enhanced the ability of the bacteria to survive in different acidic environments. Together, these findings indicate that EHEC strain EDL933 carries a prophage-encoded regulatory system that contributes to acid resistance.

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Gain-of-Function Mutations inUPC2Are a Frequent Cause ofERG11Upregulation in Azole-Resistant Clinical Isolates of Candida albicans

Eukaryotic Cell ◽

10.1128/ec.00215-12 ◽

2012 ◽

Vol 11 (10) ◽

pp. 1289-1299 ◽

Cited By ~ 105

Author(s):

Stephanie A. Flowers ◽

Katherine S. Barker ◽

Elizabeth L. Berkow ◽

Geoffrey Toner ◽

Sean G. Chadwick ◽

...

Keyword(s):

Candida Albicans ◽

Amino Acid ◽

Clinical Isolates ◽

Transcriptional Analysis ◽

Single Amino Acid ◽

Ergosterol Biosynthesis ◽

Amino Acid Substitutions ◽

Gain Of Function ◽

Content Type ◽

Zinc Cluster

ABSTRACTInCandida albicans, Upc2 is a zinc-cluster transcription factor that targets genes, including those of the ergosterol biosynthesis pathway. To date, three documentedUPC2gain-of-function (GOF) mutations have been recovered from fluconazole-resistant clinical isolates that contribute to an increase inERG11expression and decreased fluconazole susceptibility. In a group of 63 isolates with reduced susceptibility to fluconazole, we found that 47 overexpressedERG11by at least 2-fold over the average expression levels in 3 unrelated fluconazole-susceptible strains. Of those 47 isolates, 29 contained a mutation inUPC2, whereas the remaining 18 isolates did not. Among the isolates containing mutations inUPC2, we recovered eight distinct mutations resulting in putative single amino acid substitutions: G648D, G648S, A643T, A643V, Y642F, G304R, A646V, and W478C. Seven of these resulted in increasedERG11expression, increased cellular ergosterol, and decreased susceptibility to fluconazole compared to the results for the wild-type strain. Genome-wide transcriptional analysis was performed for the four strongest Upc2 amino acid substitutions (A643V, G648D, G648S, and Y642F). Genes commonly upregulated by all four mutations included those involved in ergosterol biosynthesis, in oxidoreductase activity, the major facilitator efflux pump encoded by theMDR1gene, and the uncharacterized ATP binding cassette transporterCDR11. These findings demonstrate that gain-of-function mutations inUPC2are more prevalent among clinical isolates than previously thought and make a significant contribution to azole antifungal resistance, but the findings do not account forERG11overexpression in all such isolates ofC. albicans.

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The Genomic Landscape of the Fungus-Specific SWI/SNF Complex Subunit, Snf6, in Candida albicans

mSphere ◽

10.1128/msphere.00497-17 ◽

2017 ◽

Vol 2 (6) ◽

Cited By ~ 10

Author(s):

Faiza Tebbji ◽

Yaolin Chen ◽

Adnane Sellam ◽

Malcolm Whiteway

Keyword(s):

Candida Albicans ◽

Chromatin Remodeling ◽

Opportunistic Pathogen ◽

Resistance Mechanisms ◽

Phenotypic Data ◽

Content Type ◽

Chromatin Remodeling Complex ◽

Clinical Resistance ◽

Immunosuppressed Patients

ABSTRACT Candida albicans is a natural component of the human microbiota but also an opportunistic pathogen that causes life-threatening infections in immunosuppressed patients. Current therapeutics include a limited number of molecules that suffer from limitations, including growing clinical resistance and toxicity. New molecules are being clinically investigated; however, the majority of these potential antifungals target the same processes as do the standard antifungals and might confront the same problems of toxicity and loss of efficiency due to the common resistance mechanisms. Here, we characterized the role of Snf6, a fungus-specific subunit of the chromatin-remodeling complex SWI/SNF. Our genomic and phenotypic data demonstrated a central role of Snf6 in biological processes that are critical for a fungal pathogen to colonize its host and cause disease, suggesting Snf6 as a possible antifungal target. SWI/SNF is an ATP-dependent chromatin-remodeling complex that is required for the regulation of gene expression in eukaryotes. While most of the fungal SWI/SNF components are evolutionarily conserved with those of the metazoan SWI/SNF, subunits such as Snf6 are specific to certain fungi and thus represent potential antifungal targets. We have characterized the role of the Snf6 protein in Candida albicans. Our data showed that although there was low conservation of its protein sequence with other fungal orthologs, Snf6 was copurified with bona fide SWI/SNF complex subunits. The role of Snf6 in C. albicans was investigated by determining its genome-wide occupancy using chromatin immunoprecipitation coupled to tiling arrays in addition to transcriptional profiling of the snf6 conditional mutant. Snf6 directs targets that were enriched in functions related to carbohydrate and amino acid metabolic circuits, to cellular transport, and to heat stress responses. Under hypha-promoting conditions, Snf6 expanded its set of targets to include promoters of genes related to respiration, ribosome biogenesis, mating, and vesicle transport. In accordance with the genomic occupancy data, an snf6 doxycycline-repressible mutant exhibited growth defects in response to heat stress and also when grown in the presence of different fermentable and nonfermentable carbon sources. Snf6 was also required to differentiate invasive hyphae in response to different cues. This study represents the first comprehensive characterization, at the genomic level, of the role of SWI/SNF in the pathogenic yeast C. albicans and uncovers functions that are essential for fungal morphogenesis and metabolic flexibility. IMPORTANCE Candida albicans is a natural component of the human microbiota but also an opportunistic pathogen that causes life-threatening infections in immunosuppressed patients. Current therapeutics include a limited number of molecules that suffer from limitations, including growing clinical resistance and toxicity. New molecules are being clinically investigated; however, the majority of these potential antifungals target the same processes as do the standard antifungals and might confront the same problems of toxicity and loss of efficiency due to the common resistance mechanisms. Here, we characterized the role of Snf6, a fungus-specific subunit of the chromatin-remodeling complex SWI/SNF. Our genomic and phenotypic data demonstrated a central role of Snf6 in biological processes that are critical for a fungal pathogen to colonize its host and cause disease, suggesting Snf6 as a possible antifungal target.

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Pathogenicity Genomic Island-Associated CrpP-Like Fluoroquinolone-Modifying Enzymes among Pseudomonas aeruginosa Clinical Isolates in Europe

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00489-20 ◽

2020 ◽

Vol 64 (7) ◽

Cited By ~ 1

Author(s):

José Manuel Ortiz de la Rosa ◽

Patrice Nordmann ◽

Laurent Poirel

Keyword(s):

Pseudomonas Aeruginosa ◽

Genomic Island ◽

Multidrug Resistant ◽

Resistance Mechanisms ◽

Genomic Islands ◽

Clinical Isolates ◽

Gram Negative Bacteria ◽

Gram Negative ◽

Content Type ◽

Genes Encoding

ABSTRACT Many transferable quinolone resistance mechanisms have been identified in Gram-negative bacteria. The plasmid-encoded 65-amino-acid-long ciprofloxacin-modifying enzyme CrpP was recently identified in Pseudomonas aeruginosa isolates. We analyzed a collection of 100 clonally unrelated and multidrug-resistant P. aeruginosa clinical isolates, among which 46 were positive for crpP-like genes, encoding five CrpP variants conferring variable levels of reduced susceptibility to fluoroquinolones. These crpP-like genes were chromosomally located as part of pathogenicity genomic islands.

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Human IgM Inhibits the Formation of Titan-Like Cells in Cryptococcus neoformans

Infection and Immunity ◽

10.1128/iai.00046-20 ◽

2020 ◽

Vol 88 (4) ◽

Cited By ~ 2

Author(s):

Nuria Trevijano-Contador ◽

Kaila M. Pianalto ◽

Connie B. Nichols ◽

Oscar Zaragoza ◽

J. Andrew Alspaugh ◽

...

Keyword(s):

Cell Wall ◽

Stress Response ◽

B Cell ◽

Cryptococcus Neoformans ◽

Cell Formation ◽

Transcriptional Analysis ◽

Content Type ◽

Human Immunoglobulins ◽

Genes Encoding

ABSTRACT Human studies have shown associations between cryptococcal meningitis and reduced IgM memory B cell levels, and studies in IgM- and/or B cell-deficient mice have demonstrated increased Cryptococcus neoformans dissemination from lungs to brain. Since immunoglobulins are part of the immune milieu that C. neoformans confronts in a human host, and its ability to form titan cells is an important virulence mechanism, we determined the effect of human immunoglobulins on C. neoformans titan cell formation in vitro. (i) Fluorescence microscopy showed normal human IgG and IgM bind C. neoformans. (ii) C. neoformans grown in titan cell-inducing medium with IgM, not IgG, inhibited titan-like cell formation. (iii) Absorption of IgM with laminarin or curdlan (branched and linear 1-3-beta-d-glucans, respectively) decreased this effect. (iv) Transmission electron microscopy revealed that cells grown with IgM had small capsules and unique features not seen with cells grown with IgG. (v) Comparative transcriptional analysis of cell wall, capsule, and stress response genes showed that C. neoformans grown with IgM, not IgG or phosphate-buffered saline (PBS), had decreased expression of chitin synthetase, CHS1, CHS2, and CHS8, and genes encoding cell wall carbohydrate synthetases α-1-3-glucan (AGS1) and β-1,3-glucan (FKS1). IgM also decreased expression of RIM101 and HOG1, genes encoding central regulators of C. neoformans stress response pathways and cell morphogenesis. Our data show human IgM affects C. neoformans morphology in vitro and suggest that the hypothesis that human immunoglobulins may affect C. neoformans virulence in vivo warrants further investigation.

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The Ndr/LATS Kinase Cbk1 Regulates a Specific Subset of Ace2 Functions and Suppresses the Hypha-to-Yeast Transition in Candida albicans

mBio ◽

10.1128/mbio.01900-20 ◽

2020 ◽

Vol 11 (4) ◽

Author(s):

Rohan S. Wakade ◽

Laura C. Ristow ◽

Mark A. Stamnes ◽

Anuj Kumar ◽

Damian J. Krysan

Keyword(s):

Candida Albicans ◽

Regulatory Network ◽

Transcriptional Analysis ◽

Large Set ◽

Phase Growth ◽

Content Type ◽

Hyphal Morphogenesis ◽

Specific Subset ◽

Wide Range ◽

Yeast Phase

ABSTRACT The regulation of Ace2 and morphogenesis (RAM) pathway is an important regulatory network in the human fungal pathogen Candida albicans. The RAM pathway’s two most well-studied components, the NDR/Lats kinase Cbk1 and its putative substrate, the transcription factor Ace2, have a wide range of phenotypes and functions. It is not clear, however, which of these functions are specifically due to the phosphorylation of Ace2 by Cbk1. To address this question, we first compared the transcriptional profiles of CBK1 and ACE2 deletion mutants. This analysis indicates that, of the large number of genes whose expression is affected by deletion of CBK1 and ACE2, only 5.5% of those genes are concordantly regulated. Our data also suggest that Ace2 directly or indirectly represses a large set of genes during hyphal morphogenesis. Second, we generated strains containing ACE2 alleles with alanine mutations at the Cbk1 phosphorylation sites. Phenotypic and transcriptional analysis of these ace2 mutants indicates that, as in Saccharomyces cerevisiae, Cbk1 regulation is important for daughter cell localization of Ace2 and cell separation during yeast-phase growth. In contrast, Cbk1 phosphorylation of Ace2 plays a minor role in C. albicans yeast-to-hypha transition. We have, however, discovered a new function for the Cbk1-Ace2 axis. Specifically, Cbk1 phosphorylation of Ace2 prevents the hypha-to-yeast transition. To our knowledge, this is one of the first regulators of the C. albicans hypha-to-yeast transition to be described. Finally, we present an integrated model for the role of Cbk1 in the regulation of hyphal morphogenesis in C. albicans. IMPORTANCE The regulation of Ace2 and morphogenesis (RAM) pathway is a key regulatory network that plays a role in many aspects of C. albicans pathobiology. In addition to characterizing the transcriptional effects of this pathway, we discovered that Cbk1 and Ace2, a key RAM pathway regulator-effector pair, mediate a specific set of the overall functions of the RAM pathway. We have also discovered a new function for the Cbk1-Ace2 axis: suppression of the hypha-to-yeast transition. Very few regulators of this transition have been described, and our data indicate that maintenance of hyphal morphogenesis requires suppression of yeast phase growth by Cbk1-regulated Ace2.

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Sch9 Kinase Integrates Hypoxia and CO2Sensing To Suppress Hyphal Morphogenesis in Candida albicans

Eukaryotic Cell ◽

10.1128/ec.00289-10 ◽

2011 ◽

Vol 10 (4) ◽

pp. 502-511 ◽

Cited By ~ 32

Author(s):

Catrin Stichternoth ◽

Alida Fraund ◽

Eleonora Setiadi ◽

Luc Giasson ◽

Anna Vecchiarelli ◽

...

Keyword(s):

Candida Albicans ◽

Wild Type Strain ◽

Cell Wall Proteins ◽

Content Type ◽

Chronological Aging ◽

Hyphal Morphogenesis ◽

Hypha Formation ◽

Virulence Trait ◽

Genes Encoding ◽

A Minor

ABSTRACTThe yeast-hypha transition is an important virulence trait ofCandida albicans. We report that the AGC kinase Sch9 prevents hypha formation specifically under hypoxia at high CO2levels.sch9mutants showed no major defects in growth and stress resistance but a striking hyperfilamentous phenotype under hypoxia (<10% O2), although only in the presence of elevated CO2levels (>1%) and at temperatures of <37°C during surface growth. Thesch9hyperfilamentous phenotype was independent of Rim15 kinase and was recreated by inhibition of Tor1 kinase by rapamycin or caffeine in a wild-type strain, suggesting that Sch9 suppression requires Tor1. Caffeine inhibition also revealed that both protein kinase A isoforms, as well as transcription factors Czf1 and Ace2, are required to generate thesch9mutant phenotype. Transcriptomal analyses showed that Sch9 regulates most genes solely under hypoxia and in the presence of elevated CO2. In this environment, Sch9 downregulates genes encoding cell wall proteins and nutrient transporters, while under normoxia Sch9 and Tor1 coregulate a minor fraction of Sch9-regulated genes, e.g., by inducing glycolytic genes. Other than inSaccharomyces cerevisiae, bothsch9andrim15mutants showed decreased chronological aging under normoxia but not under hypoxia, indicating significant rewiring of the Tor1-Sch9-Rim15 pathway inC. albicans. The results stress the importance of environmental conditions on Sch9 function and establish a novel response circuitry to both hypoxia and CO2inC. albicans, which suppresses hypha formation but also allows efficient nutrient uptake, metabolism, and virulence.

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Evolution of Fluconazole-ResistantCandida albicansStrains by Drug-Induced Mating Competence and Parasexual Recombination

mBio ◽

10.1128/mbio.02740-18 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 12

Author(s):

Christina Popp ◽

Bernardo Ramírez-Zavala ◽

Sonja Schwanfelder ◽

Ines Krüger ◽

Joachim Morschhäuser

Keyword(s):

Drug Resistance ◽

Mating Type ◽

Acquired Resistance ◽

Resistance Mechanisms ◽

Drug Resistant ◽

Resistance Mutations ◽

Type Locus ◽

Content Type ◽

Mating Type Locus ◽

Resistant Progeny

ABSTRACTThe clonal population structure ofCandida albicanssuggests that (para)sexual recombination does not play an important role in the lifestyle of this opportunistic fungal pathogen, an assumption that is strengthened by the fact that mostC. albicansstrains are heterozygous at the mating type locus (MTL) and therefore mating-incompetent. On the other hand, mating might occur within clonal populations and allow the combination of advantageous traits that were acquired by individual cells to adapt to adverse conditions. We have investigated if parasexual recombination may be involved in the evolution of highly drug-resistant strains exhibiting multiple resistance mechanisms against fluconazole, an antifungal drug that is commonly used to treat infections byC. albicans. Growth of strains that were heterozygous forMTLand different fluconazole resistance mutations in the presence of the drug resulted in the emergence of derivatives that had become homozygous for the mutated allele and the mating type locus and exhibited increased drug resistance. WhenMTLa/aandMTLα/α cells of these strains were mixed in all possible combinations, we could isolate mating products containing the genetic material from both parents. The initial mating products did not exhibit higher drug resistance than their parental strains, but further propagation under selective pressure resulted in the loss of the wild-type alleles and increased fluconazole resistance. Therefore, fluconazole treatment not only selects for resistance mutations but also promotes genomic alterations that confer mating competence, which allows cells in an originally clonal population to exchange individually acquired resistance mechanisms and generate highly drug-resistant progeny.IMPORTANCESexual reproduction is an important mechanism in the evolution of species, since it allows the combination of advantageous traits of individual members in a population. The pathogenic yeastCandida albicansis a diploid organism that normally propagates in a clonal fashion, because heterozygosity at the mating type locus (MTL) inhibits mating between cells. Here we show thatC. albicanscells that have acquired drug resistance mutations during treatment with the commonly used antifungal agent fluconazole rapidly develop further increased resistance by genome rearrangements that result in simultaneous loss of heterozygosity for the mutated allele and the mating type locus. This enables the drug-resistant cells of a population to switch to the mating-competent opaque morphology and mate with each other to combine different individually acquired resistance mechanisms. The tetraploid mating products reassort their merged genomes and, under selective pressure by the drug, generate highly resistant progeny that have retained the advantageous mutated alleles. Parasexual propagation, promoted by stress-induced genome rearrangements that result in the acquisition of mating competence in cells with adaptive mutations, may therefore be an important mechanism in the evolution ofC. albicanspopulations.

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