Deletion of the fungus specific protein phosphatase Z1 exaggerates the oxidative stress response in Candida albicans

Comparative Small RNA and Degradome Sequencing Provides Insights into Antagonistic Interactions in the Biocontrol Fungus Clonostachys rosea

Necrotrophic mycoparasitism is an intricate process involving recognition, physical mycelial contact, and killing of host fungi (mycohosts). During such interactions, mycoparasites undergo a complex developmental process involving massive regulatory changes of gene expression to produce a range of chemical compounds and proteins that contribute to the parasitism of the mycohosts. Small RNAs (sRNAs) are vital components of posttranscriptional gene regulation, although their role in gene expression regulation during mycoparasitisms remain understudied. Here, we investigated the role of sRNA-mediated gene regulation in mycoparasitism by performing sRNA and degradome tag sequencing of the mycoparasitic fungus Clonostachys rosea interacting with the plant-pathogenic mycohosts Botrytis cinerea and Fusarium graminearum at two time points. The majority of differentially expressed sRNAs were downregulated during the interactions with the mycohosts compared to a C. rosea self-interaction control, thus allowing desuppression (upregulation) of mycohost-responsive genes. Degradome analysis showed a positive correlation between high degradome counts and antisense sRNA mapping and led to the identification of 201 sRNA-mediated potential gene targets for 282 differentially expressed sRNAs. Analysis of sRNA potential gene targets revealed that the regulation of genes coding for membrane proteins was a common response against both mycohosts. The regulation of genes involved in oxidative stress tolerance and cellular metabolic and biosynthetic processes was exclusive against F. graminearum, highlighting common and mycohost-specific gene regulation of C. rosea. By combining these results with transcriptome data collected during a previous study, we expand the understanding of the role of sRNA in regulating interspecific fungal interactions and mycoparasitism.

IMPORTANCE Small RNAs (sRNAs) are emerging as key players in pathogenic and mutualistic fungus-plant interactions; however, their role in fungus-fungus interactions remains elusive. In this study, we employed the necrotrophic mycoparasite Clonostachys rosea and the plant-pathogenic mycohosts Botrytis cinerea and Fusarium graminearum and investigated the sRNA-mediated gene regulation in mycoparasitic interactions. The combined approach of sRNA and degradome tag sequencing identified 201 sRNA-mediated putative gene targets for 282 differentially expressed sRNAs, highlighting the role of sRNA-mediated regulation of mycoparasitism in C. rosea. We also identified 36 known and 13 novel microRNAs (miRNAs) and their potential gene targets at the endogenous level and at a cross-species level in B. cinerea and F. graminearum, indicating a role of cross-species RNA interference (RNAi) in mycoparasitism, representing a novel mechanism in biocontrol interactions. Furthermore, we showed that C. rosea adapts its transcriptional response, and thereby its interaction mechanisms, based on the interaction stages and identity of the mycohost.

Biophysical experiments reveal a protective role of protein phosphatase Z1 against oxidative damage of the cell membrane in Candida albicans

Protein phosphatase Z1 (Ppz1) has been shown to take part in important physiological functions in fungi including a contribution to virulence of Candida albicans. Although its involvement in the oxidative stress response has also been documented, the exact mechanism of action of its protective effect against oxidative damage remains unknown. By developing a pipeline to analyze the biophysical properties of the cell membrane in fungi, we demonstrate that the plasma membrane of Ppz1-KO Candida albicans displays increased sensitivity to tert-butyl-hydroperoxide-induced oxidative damage. In particular, the response to the oxidizing agent, characterized by increased lipid peroxidation, reduced lipid order, and inhibited lateral mobility of plasma membrane components, is significantly more pronounced in the Ppz1-KO C. albicans strain than in the wild-type counterpart. Remarkably, membrane constituents became almost completely immobile in the phosphatase deletion mutant exposed to oxidative stress. Furthermore, moderately elevated membrane lipid peroxidation accompanied by the aforementioned changes in the biophysical characteristics of the plasma membrane are already detectable in untreated Ppz1-KO cells indicating latent membrane damage even in the absence of oxidative stress. In conclusion, the hypersensitivity of cells lacking Ppz1 to oxidative damage establishes that potential Ppz1 inhibitors may synergize with oxidizing agents in prospective anti-fungal combination therapies.

Transcriptional Profiling of the Candida auris Response to Exogenous Farnesol Exposure

The antifungal resistance threat posed by Candida auris necessitates bold and innovative therapeutic options. Farnesol is a quorum-sensing molecule with a potential antifungal and/or adjuvant effect; it may be a promising candidate in alternative treatment regimens. To gain further insights into the farnesol-related effect on C. auris, genome-wide gene transcription analysis was performed using transcriptome sequencing (RNA-Seq). Farnesol exposure resulted in 1,766 differentially expressed genes. Of these genes, 447 and 304 genes with at least 1.5-fold increase or decrease in transcription, respectively, were selected for further investigation. Genes involved in morphogenesis, biofilm events (maturation and dispersion), gluconeogenesis, iron metabolism, and regulation of RNA biosynthesis showed downregulation, whereas those related to antioxidative defense, transmembrane transport, glyoxylate cycle, fatty acid β-oxidation, and peroxisome processes were upregulated. In addition, farnesol treatment increased the transcription of certain efflux pump genes, including MDR1, CDR1, and CDR2. Growth, measured by the change in the number of CFU, was significantly inhibited within 2 h of the addition of farnesol (5.8 × 10⁷ ± 1.1 × 10⁷ and 1.1 × 10⁷ ± 0.3 × 10⁷ CFU/ml for untreated control and farnesol-exposed cells, respectively) (P < 0.001). In addition, farnesol treatment caused a significant reduction in intracellular iron (152.2 ± 21.1 versus 116.0 ± 10.0 mg/kg), manganese (67.9 ± 5.1 versus 18.6 ± 1.8 mg/kg), and zinc (787.8 ± 22.2 versus 245.8 ± 34.4 mg/kg) (P < 0.05 to 0.001) compared to untreated control cells, whereas the level of cooper was significantly increased (274.6 ± 15.7 versus 828.8 ± 106.4 mg/kg) (P < 0.001). Our data demonstrate that farnesol significantly influences the growth, intracellular metal ion contents, and gene transcription related to fatty acid metabolism, which could open new directions in developing alternative therapies against C. auris.

IMPORTANCECandida auris is a dangerous fungal pathogen that causes outbreaks in health care facilities, with infections associated with a high mortality rate. As conventional antifungal drugs have limited effects against the majority of clinical isolates, new and innovative therapies are urgently needed. Farnesol is a key regulator molecule of fungal morphogenesis, inducing phenotypic adaptations and influencing biofilm formation as well as virulence. Alongside these physiological modulations, it has a potent antifungal effect alone or in combination with traditional antifungals, especially at supraphysiological concentrations. However, our knowledge about the mechanisms underlying this antifungal effect against C. auris is limited. This study has demonstrated that farnesol enhances the oxidative stress and reduces the fungal survival strategies. Furthermore, it inhibits manganese, zinc transport, and iron metabolism as well as increases fungal intracellular copper content. In addition, metabolism was modulated toward β-oxidation. These results provide definitive explanations for the observed antifungal effects.

The Negative Effect of Protein Phosphatase Z1 Deletion on the Oxidative Stress Tolerance of Candida albicans Is Synergistic with Betamethasone Exposure

The glucocorticoid betamethasone (BM) has potent anti-inflammatory and immunosuppressive effects; however, it increases the susceptibility of patients to superficial Candida infections. Previously we found that this disadvantageous side effect can be counteracted by menadione sodium bisulfite (MSB) induced oxidative stress treatment. The fungus specific protein phosphatase Z1 (CaPpz1) has a pivotal role in oxidative stress response of Candida albicans and was proposed as a potential antifungal drug target. The aim of this study was to investigate the combined effects of CaPPZ1 gene deletion and MSB treatment in BM pre-treated C. albicans cultures. We found that the combined treatment increased redox imbalance, enhanced the specific activities of antioxidant enzymes, and reduced the growth in cappz1 mutant (KO) strain. RNASeq data demonstrated that the presence of BM markedly elevated the number of differentially expressed genes in the MSB treated KO cultures. Accumulation of reactive oxygen species, increased iron content and fatty acid oxidation, as well as the inhibiting ergosterol biosynthesis and RNA metabolic processes explain, at least in part, the fungistatic effect caused by the combined stress exposure. We suggest that the synergism between MSB treatment and CaPpz1 inhibition could be considered in developing of a novel combinatorial antifungal strategy accompanying steroid therapy.

Prospecting Biomarkers for Diagnostic and Therapeutic Approaches in Pythiosis

Pythiosis, whose etiological agent is the oomycete Pythium insidiosum, is a life-threatening disease that occurs mainly in tropical and subtropical countries, affecting several animal species. It is frequently found in horses in Brazil and humans in Thailand. The disease is difficult to diagnose because the pathogen’s hyphae are often misdiagnosed as mucoromycete fungi in histological sections. Additionally, there is no specific antigen to use for rapid diagnosis, the availability of which could improve the prognosis in different animal species. In this scenario, we investigated which P. insidiosum antigens are recognized by circulating antibodies in horses and humans with pythiosis from Brazil and Thailand, respectively, using 2D immunoblotting followed by mass spectrometry for the identification of antigens. We identified 23 protein spots, 14 recognized by pooled serum from horses and humans. Seven antigens were commonly recognized by both species, such as the heat-shock cognate 70 KDa protein, the heat-shock 70 KDa protein, glucan 1,3-beta-glucosidase, fructose-bisphosphate aldolase, serine/threonine-protein phosphatase, aconitate hydratase, and 14-3-3 protein epsilon. These results demonstrate that there are common antigens recognized by the immune responses of horses and humans, and these antigens may be studied as biomarkers for improving diagnosis and treatment.

Intraspecies Transcriptional Profiling Reveals Key Regulators of Candida albicans Pathogenic Traits

The human commensal and opportunistic fungal pathogen Candida albicans displays extensive genetic and phenotypic variation across clinical isolates. Here, we performed RNA sequencing on 21 well-characterized isolates to examine how genetic variation contributes to gene expression differences and to link these differences to phenotypic traits. C. albicans adapts primarily through clonal evolution, and yet hierarchical clustering of gene expression profiles in this set of isolates did not reproduce their phylogenetic relationship. Strikingly, strain-specific gene expression was prevalent in some strain backgrounds. Association of gene expression with phenotypic data by differential analysis, linear correlation, and assembly of gene networks connected both previously characterized and novel genes with 23 C. albicans traits. Construction of de novo gene modules produced a gene atlas incorporating 67% of C. albicans genes and revealed correlations between expression modules and important phenotypes such as systemic virulence. Furthermore, targeted investigation of two modules that have novel roles in growth and filamentation supported our bioinformatic predictions. Together, these studies reveal widespread transcriptional variation across C. albicans isolates and identify genetic and epigenetic links to phenotypic variation based on coexpression network analysis.IMPORTANCE Infectious fungal species are often treated uniformly despite clear evidence of genotypic and phenotypic heterogeneity being widespread across strains. Identifying the genetic basis for this phenotypic diversity is extremely challenging because of the tens or hundreds of thousands of variants that may distinguish two strains. Here, we use transcriptional profiling to determine differences in gene expression that can be linked to phenotypic variation among a set of 21 Candida albicans isolates. Analysis of this transcriptional data set uncovered clear trends in gene expression characteristics for this species and new genes and pathways that were associated with variation in pathogenic processes. Direct investigation confirmed functional predictions for a number of new regulators associated with growth and filamentation, demonstrating the utility of these approaches in linking genes to important phenotypes.