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Carbon Catabolite Repression in Filamentous Fungi Is Regulated by Phosphorylation of the Transcription Factor CreA.
FungiNet total, A1, Z2

Abstract (Expand)

Filamentous fungi of the genus Aspergillus are of particular interest for biotechnological applications due to their natural capacity to secrete carbohydrate-active enzymes (CAZy) that target plant … biomass. The presence of easily metabolizable sugars such as glucose, whose concentrations increase during plant biomass hydrolysis, results in the repression of CAZy-encoding genes in a process known as carbon catabolite repression (CCR), which is undesired for the purpose of large-scale enzyme production. To date, the C2H2 transcription factor CreA has been described as the major CC repressor in Aspergillus spp., although little is known about the role of posttranslational modifications in this process. In this work, phosphorylation sites were identified by mass spectrometry on Aspergillus nidulans CreA, and subsequently, the previously identified but uncharacterized site S262, the characterized site S319, and the newly identified sites S268 and T308 were chosen to be mutated to nonphosphorylatable residues before their effect on CCR was investigated. Sites S262, S268, and T308 are important for CreA protein accumulation and cellular localization, DNA binding, and repression of enzyme activities. In agreement with a previous study, site S319 was not important for several here-tested phenotypes but is key for CreA degradation and induction of enzyme activities. All sites were shown to be important for glycogen and trehalose metabolism. This study highlights the importance of CreA phosphorylation sites for the regulation of CCR. These sites are interesting targets for biotechnological strain engineering without the need to delete essential genes, which could result in undesired side effects.IMPORTANCE In filamentous fungi, the transcription factor CreA controls carbohydrate metabolism through the regulation of genes encoding enzymes required for the use of alternative carbon sources. In this work, phosphorylation sites were identified on Aspergillus nidulans CreA, and subsequently, the two newly identified sites S268 and T308, the previously identified but uncharacterized site S262, and the previously characterized site S319 were chosen to be mutated to nonphosphorylatable residues before their effect on CCR was characterized. Sites S262, S268, and T308 are important for CreA protein accumulation and cellular localization, DNA binding, and repression of enzyme activities. In agreement with a previous study, site S319 is not important for several here-tested phenotypes but is key for CreA degradation and induction of enzyme activities. This work characterized novel CreA phosphorylation sites under carbon catabolite-repressing conditions and showed that they are crucial for CreA protein turnover, control of carbohydrate utilization, and biotechnologically relevant enzyme production.

Authors: L. J. de Assis, L. P. Silva, O. Bayram, P. Dowling, Olaf Kniemeyer, Thomas Krüger, Axel Brakhage, Y. Chen, L. Dong, K. Tan, K. H. Wong, L. N. A. Ries, G. H. Goldman

Date Published: 5th Jan 2021

Journal: mBio

Comparison of the central human and mouse platelet signaling cascade by systems biological analysis.
B2

Abstract (Expand)

BACKGROUND: Understanding the molecular mechanisms of platelet activation and aggregation is of high interest for basic and clinical hemostasis and thrombosis research. The central platelet protein … interaction network is involved in major responses to exogenous factors. This is defined by systemsbiological pathway analysis as the central regulating signaling cascade of platelets (CC). RESULTS: The CC is systematically compared here between mouse and human and major differences were found. Genetic differences were analysed comparing orthologous human and mouse genes. We next analyzed different expression levels of mRNAs. Considering 4 mouse and 7 human high-quality proteome data sets, we identified then those major mRNA expression differences (81%) which were supported by proteome data. CC is conserved regarding genetic completeness, but we observed major differences in mRNA and protein levels between both species. Looking at central interactors, human PLCB2, MMP9, BDNF, ITPR3 and SLC25A6 (always Entrez notation) show absence in all murine datasets. CC interactors GNG12, PRKCE and ADCY9 occur only in mice. Looking at the common proteins, TLN1, CALM3, PRKCB, APP, SOD2 and TIMP1 are higher abundant in human, whereas RASGRP2, ITGB2, MYL9, EIF4EBP1, ADAM17, ARRB2, CD9 and ZYX are higher abundant in mouse. Pivotal kinase SRC shows different regulation on mRNA and protein level as well as ADP receptor P2RY12. CONCLUSIONS: Our results highlight species-specific differences in platelet signaling and points of specific fine-tuning in human platelets as well as murine-specific signaling differences.

Authors: J. Balkenhol, K. V. Kaltdorf, E. Mammadova-Bach, A. Braun, B. Nieswandt, M. Dittrich, T. Dandekar

Date Published: 22nd Dec 2020

Journal: BMC Genomics

Comparative Transcriptomic Analysis of Rhinovirus and Influenza Virus Infection.
INF, B5

Abstract (Expand)

Rhinovirus (RV) and influenza virus are the most frequently detected respiratory viruses among adult patients with community acquired pneumonia. Previous clinical studies have identified major differences … in the clinical presentations and inflammatory or immune response during these infections. A systematic transcriptomic analysis directly comparing influenza and RV is lacking. Here, we sought to compare the transcriptomic response to these viral infections. Human airway epithelial Calu-3 cells were infected with contemporary clinical isolates of RV, influenza A virus (IAV), or influenza B virus (IBV). Host gene expression was determined using RNA-seq. Differentially expressed genes (DEGs) with respect to mock-infected cells were identified using the overlapping gene-set of four different statistical models. Transcriptomic analysis showed that RV-infected cells have a more blunted host response with fewer DEGs than IAV or IBV-infected cells. IFNL1 and CXCL10 were among the most upregulated DEGs during RV, IAV, and IBV infection. Other DEGs that were highly expressed for all 3 viruses were mainly genes related to type I or type III interferons (RSAD2, IDO1) and chemokines (CXCL11). Notably, ICAM5, a known receptor for enterovirus D68, was highly expressed during RV infection only. Gene Set Enrichment Analysis (GSEA) confirmed that pathways associated with interferon response, innate immunity, or regulation of inflammatory response, were most perturbed for all three viruses. Network analysis showed that steroid-related pathways were enriched. Taken together, our data using contemporary virus strains suggests that genes related to interferon and chemokine predominated the host response associated with RV, IAV, and IBV infection. Several highly expressed genes, especially ICAM5 which is preferentially-induced during RV infection, deserve further investigation.

Authors: T. K. Dissanayake, Sascha Schäuble, Mohammad Mirhakkak, W. L. Wu, A. C. Ng, C. C. Y. Yip, A. G. Lopez, Thomas Wolf, M. L. Yeung, K. H. Chan, K. Y. Yuen, Gianni Panagiotou, K. K. To

Date Published: 28th Aug 2020

Journal: Front Microbiol

Catch the wave: Metabolomic analyses in human pathogenic fungi.
C2

Abstract

Not specified

Authors: Philipp Brandt, E. Garbe, Slavena Vylkova

Date Published: 21st Aug 2020

Journal: PLoS Pathog

Clinical Candida albicans Vaginal Isolates and a Laboratory Strain Show Divergent Behaviors during Macrophage Interactions.
FungiNet C - Candida projects

Abstract (Expand)

Typically, established lab strains are widely used to study host-pathogen interactions. However, to better reflect the infection process, the experimental use of clinical isolates has come more into … focus. Here, we analyzed the interaction of multiple vaginal isolates of the opportunistic fungal pathogen Candida albicans, the most common cause of vulvovaginal candidiasis in women, with key players of the host immune system: macrophages. We tested several strains isolated from asymptomatic or symptomatic women with acute and recurrent infections. While all clinical strains showed a response similar to the commonly used lab strain SC5314 in various in vitro assays, they displayed remarkable differences during interaction with macrophages. This coincided with significantly reduced beta-glucan exposure on the cell surface, which appeared to be a shared property among the tested vaginal strains for yeast extract/peptone/dextrose-grown cells, which is partly lost when the isolates faced vaginal niche-like nutrient conditions. However, macrophage damage, survival of phagocytosis, and filamentation capacities were highly strain-specific. These results highlight the high heterogeneity of C. albicans strains in host-pathogen interactions, which have to be taken into account to bridge the gap between laboratory-gained data and disease-related outcomes in an actual patient.IMPORTANCE Vulvovaginal candidiasis is one of the most common fungal infections in humans with Candida albicans as the major causative agent. This study is the first to compare clinical vaginal isolates of defined patient groups in their interaction with macrophages, highlighting the vastly different outcomes in comparison to a laboratory strain using commonly applied virulence-determining assays.

Authors: F. Gerwien, C. Dunker, Philipp Brandt, E. Garbe, Ilse Jacobsen, Slavena Vylkova

Date Published: 19th Aug 2020

Journal: mSphere

Candida Species-Dependent Release of IL-12 by Dendritic Cells Induces Different Levels of NK Cell Stimulation.
A2, B4, C3

Abstract (Expand)

BACKGROUND: Candida albicans and Candida glabrata are the 2 most prevalent Candida species causing bloodstream infections. Patterns of innate immune activation triggered by the 2 fungi differ considerably. … METHODS: To analyze human natural killer (NK) cell activation by both species, we performed ex vivo whole-blood infection assays and confrontation assays with primary human NK cells. RESULTS: C. albicans was a stronger activator for isolated human NK cells than C. glabrata. In contrast, activation of blood NK cells, characterized by an upregulated surface exposure of early activation antigen CD69 and death receptor ligand TRAIL, as well as interferon-gamma (IFN-gamma) secretion, was more pronounced during C. glabrata infection. NK cell activation in blood is mediated by humoral mediators released by other immune cells and does not depend on direct activation by fungal cells. Cross-talk between Candida-confronted monocyte-derived dendritic cells (moDC) and NK cells resulted in the same NK activation phenotype as NK cells in human blood. Blocking experiments and cytokine substitution identified interleukin-12 as a critical mediator in regulation of primary NK cells by moDC. CONCLUSIONS: Activation of human NK cells in response to Candida in human blood mainly occurs indirectly by mediators released from monocytic cells.

Authors: A. Marolda, Kerstin Hünniger, S. Bottcher, W. Vivas, Jürgen Löffler, Marc Thilo Figge, Oliver Kurzai

Date Published: 11th Jun 2020

Journal: J Infect Dis

covRNA: discovering covariate associations in large-scale gene expression data.
B2

Abstract (Expand)

OBJECTIVE: The biological interpretation of gene expression measurements is a challenging task. While ordination methods are routinely used to identify clusters of samples or co-expressed genes, these … methods do not take sample or gene annotations into account. We aim to provide a tool that allows users of all backgrounds to assess and visualize the intrinsic correlation structure of complex annotated gene expression data and discover the covariates that jointly affect expression patterns. RESULTS: The Bioconductor package covRNA provides a convenient and fast interface for testing and visualizing complex relationships between sample and gene covariates mediated by gene expression data in an entirely unsupervised setting. The relationships between sample and gene covariates are tested by statistical permutation tests and visualized by ordination. The methods are inspired by the fourthcorner and RLQ analyses used in ecological research for the analysis of species abundance data, that we modified to make them suitable for the distributional characteristics of both, RNA-Seq read counts and microarray intensities, and to provide a high-performance parallelized implementation for the analysis of large-scale gene expression data on multi-core computational systems. CovRNA provides additional modules for unsupervised gene filtering and plotting functions to ensure a smooth and coherent analysis workflow.

Authors: L. Urban, Christian Remmele, Marcus Dittrich, R. F. Schwarz, Tobias Müller

Date Published: 24th Feb 2020

Journal: BMC Res Notes

Comparative Assessment of Aspergillosis by Virtual Infection Modeling in Murine and Human Lung.
B4

Abstract (Expand)

Aspergillus fumigatus is a ubiquitous opportunistic fungal pathogen that can cause severe infections in immunocompromised patients. Conidia that reach the lower respiratory tract are confronted with … alveolar macrophages, which are the resident phagocytic cells, constituting the first line of defense. If not efficiently removed in time, A. fumigatus conidia can germinate causing severe infections associated with high mortality rates. Mice are the most extensively used model organism in research on A. fumigatus infections. However, in addition to structural differences in the lung physiology of mice and the human host, applied infection doses in animal experiments are typically orders of magnitude larger compared to the daily inhalation doses of humans. The influence of these factors, which must be taken into account in a quantitative comparison and knowledge transfer from mice to humans, is difficult to measure since in vivo live cell imaging of the infection dynamics under physiological conditions is currently not possible. In the present study, we compare A. fumigatus infection in mice and humans by virtual infection modeling using a hybrid agent-based model that accounts for the respective lung physiology and the impact of a wide range of infection doses on the spatial infection dynamics. Our computer simulations enable comparative quantification of A. fumigatus infection clearance in the two hosts to elucidate (i) the complex interplay between alveolar morphometry and the fungal burden and (ii) the dynamics of infection clearance, which for realistic fungal burdens is found to be more efficiently realized in mice compared to humans.

Authors: M. Blickensdorf, Sandra Timme, Marc Thilo Figge

Date Published: 27th Feb 2019

Journal: Front Immunol

Coding of Experimental Conditions in Microfluidic Droplet Assays Using Colored Beads and Machine Learning Supported Image Analysis.
B4

Abstract (Expand)

To efficiently exploit the potential of several millions of droplets that can be considered as individual bioreactors in microfluidic experiments, methods to encode different experimental conditions … in droplets are needed. The approach presented here is based on coencapsulation of colored polystyrene beads with biological samples. The decoding of the droplets, as well as content quantification, are performed by automated analysis of triggered images of individual droplets in-flow using bright-field microscopy. The decoding strategy combines bead classification using a random forest classifier and Bayesian inference to identify different codes and thus experimental conditions. Antibiotic susceptibility testing of nine different antibiotics and the determination of the minimal inhibitory concentration of a specific antibiotic against a laboratory strain of Escherichia coli are presented as a proof-of-principle. It is demonstrated that this method allows successful encoding and decoding of 20 different experimental conditions within a large droplet population of more than 10(5) droplets per condition. The decoding strategy correctly assigns 99.6% of droplets to the correct condition and a method for the determination of minimal inhibitory concentration using droplet microfluidics is established. The current encoding and decoding pipeline can readily be extended to more codes by adding more bead colors or color combinations.

Authors: Carl-Magnus Svensson, O. Shvydkiv, Stefanie Dietrich, L. Mahler, T. Weber, M. Choudhary, M. Tovar, Marc Thilo Figge, M. Roth

Date Published: 15th Dec 2018

Journal: Small

Comparative Study on Alternative Splicing in Human Fungal Pathogens Suggests Its Involvement During Host Invasion.
INF, B1

Abstract (Expand)

Alternative splicing (AS) is an important regulatory mechanism in eukaryotes but only little is known about its impact in fungi. Human fungal pathogens are of high clinical interest causing recurrent … or life-threatening infections. AS can be well-investigated genome-wide and quantitatively with the powerful technology of RNA-Seq. Here, we systematically studied AS in human fungal pathogens based on RNA-Seq data. To do so, we investigated its effect in seven fungi during conditions simulating ex vivo infection processes and during in vitro stress. Genes undergoing AS are species-specific and act independently from differentially expressed genes pointing to an independent mechanism to change abundance and functionality. Candida species stand out with a low number of introns with higher and more varying lengths and more alternative splice sites. Moreover, we identified a functional difference between response to host and other stress conditions: During stress, AS affects more genes and is involved in diverse regulatory functions. In contrast, during response-to-host conditions, genes undergoing AS have membrane functionalities and might be involved in the interaction with the host. We assume that AS plays a crucial regulatory role in pathogenic fungi and is important in both response to host and stress conditions.

Authors: Patricia Sieber, Kerstin Voigt, P. Kammer, S. Brunke, Stefan Schuster, Jörg Linde

Date Published: 19th Oct 2018

Journal: Front Microbiol

Candida albicans-Induced Epithelial Damage Mediates Translocation through Intestinal Barriers.
B4

Abstract (Expand)

Life-threatening systemic infections often occur due to the translocation of pathogens across the gut barrier and into the bloodstream. While the microbial and host mechanisms permitting bacterial gut … translocation are well characterized, these mechanisms are still unclear for fungal pathogens such as Candida albicans, a leading cause of nosocomial fungal bloodstream infections. In this study, we dissected the cellular mechanisms of translocation of C. albicans across intestinal epithelia in vitro and identified fungal genes associated with this process. We show that fungal translocation is a dynamic process initiated by invasion and followed by cellular damage and loss of epithelial integrity. A screen of >2,000 C. albicans deletion mutants identified genes required for cellular damage of and translocation across enterocytes. Correlation analysis suggests that hypha formation, barrier damage above a minimum threshold level, and a decreased epithelial integrity are required for efficient fungal translocation. Translocation occurs predominantly via a transcellular route, which is associated with fungus-induced necrotic epithelial damage, but not apoptotic cell death. The cytolytic peptide toxin of C. albicans, candidalysin, was found to be essential for damage of enterocytes and was a key factor in subsequent fungal translocation, suggesting that transcellular translocation of C. albicans through intestinal layers is mediated by candidalysin. However, fungal invasion and low-level translocation can also occur via non-transcellular routes in a candidalysin-independent manner. This is the first study showing translocation of a human-pathogenic fungus across the intestinal barrier being mediated by a peptide toxin.IMPORTANCECandida albicans, usually a harmless fungus colonizing human mucosae, can cause lethal bloodstream infections when it manages to translocate across the intestinal epithelium. This can result from antibiotic treatment, immune dysfunction, or intestinal damage (e.g., during surgery). However, fungal processes may also contribute. In this study, we investigated the translocation process of C. albicans using in vitro cell culture models. Translocation occurs as a stepwise process starting with invasion, followed by epithelial damage and loss of epithelial integrity. The ability to secrete candidalysin, a peptide toxin deriving from the hyphal protein Ece1, is key: C. albicans hyphae, secreting candidalysin, take advantage of a necrotic weakened epithelium to translocate through the intestinal layer.

Authors: Stefanie Allert, Toni Förster, Carl-Magnus Svensson, J. P. Richardson, T. Pawlik, B. Hebecker, Sven Rudolphi, M. Juraschitz, M. Schaller, M. Blagojevic, Joachim Morschhäuser, Marc Thilo Figge, Ilse Jacobsen, J. R. Naglik, Lydia Kasper, Selene Mogavero, Bernhard Hube

Date Published: 5th Jun 2018

Journal: mBio

Candida albicans Induces Metabolic Reprogramming in Human NK Cells and Responds to Perforin with a Zinc Depletion Response
FungiNet A - Aspergillus projects, FungiNet C - Candida projects

Abstract (Expand)

As part of the innate immune system, natural killer (NK) cells are directly involved in the response to fungal infections. Perforin has been identified as the major effector molecule acting against … many fungal pathogens. While several studies have shown that perforin mediated fungicidal effects can contribute to fungal clearance, neither the activation of NK cells by fungal pathogens nor the effects of perforin on fungal cells are well-understood. In a dual approach, we have studied the global gene expression pattern of primary and cytokine activated NK cells after co-incubation with Candida albicans and the transcriptomic adaptation of C. albicans to perforin exposure. NK cells responded to the fungal pathogen with an up-regulation of genes involved in immune signaling and release of cytokines. Furthermore, we observed a pronounced increase of genes involved in glycolysis and glycolysis inhibitor 2-deoxy-D-glucose impaired C. albicans induced NK cell activation. This strongly indicates that metabolic adaptation is a major part of the NK cell response to C. albicans infections. In the fungal pathogen, perforin induced a strong up-regulation of several fungal genes involved in the zinc depletion response, such as PRA1 and ZRT1. These data suggest that fungal zinc homeostasis is linked to the reaction to perforin secreted by NK cells. However, deletion mutants in PRA1 and ZRT1 did not show altered susceptibility to perforin.

Authors: Dragana Slavkovic Lukic, J. Voigt, M. Bouzani, Jürgen Löffler, Daniela Albrecht-Eckardt, Michael Weber, Stefanie Allert, R. Martin, Oliver Kurzai, Kerstin Hünniger

Date Published: 19th May 2016

Journal: Front Microbiol

Candidalysin is a fungal peptide toxin critical for mucosal infection
FungiNet C - Candida projects

Abstract (Expand)

Cytolytic proteins and peptide toxins are classical virulence factors of several bacterial pathogens which disrupt epithelial barrier function, damage cells and activate or modulate host immune responses. … Such toxins have not been identified previously in human pathogenic fungi. Here we identify the first, to our knowledge, fungal cytolytic peptide toxin in the opportunistic pathogen Candida albicans. This secreted toxin directly damages epithelial membranes, triggers a danger response signalling pathway and activates epithelial immunity. Membrane permeabilization is enhanced by a positive charge at the carboxy terminus of the peptide, which triggers an inward current concomitant with calcium influx. C. albicans strains lacking this toxin do not activate or damage epithelial cells and are avirulent in animal models of mucosal infection. We propose the name 'Candidalysin' for this cytolytic peptide toxin; a newly identified, critical molecular determinant of epithelial damage and host recognition of the clinically important fungus, C. albicans.

Authors: D. L. Moyes, D. Wilson, J. P. Richardson, S. Mogavero, S. X. Tang, J. Wernecke, S. Hofs, R. L. Gratacap, J. Robbins, M. Runglall, C. Murciano, M. Blagojevic, S. Thavaraj, Toni Förster, B. Hebecker, Lydia Kasper, G. Vizcay, S. I. Iancu, N. Kichik, A. Hader, Oliver Kurzai, T. Luo, T. Kruger, O. Kniemeyer, E. Cota, O. Bader, R. T. Wheeler, T. Gutsmann, Bernhard Hube, J. R. Naglik

Date Published: 30th Mar 2016

Journal: Nature

Candida albicans infection leads to barrier breakdown and a MAPK/NF-kappaB mediated stress response in the intestinal epithelial cell line C2BBe1
FungiNet B - Bioinformatics projects, INF

Abstract (Expand)

Intestinal epithelial cells (IEC) form a tight barrier to the gut lumen. Paracellular permeability of the intestinal barrier is regulated by tight junction proteins and can be modulated by microorganisms … and other stimuli. The polymorphic fungus Candida albicans, a frequent commensal of the human mucosa has the capacity of traversing this barrier and establishing systemic disease within the host. Infection of polarized C2BBe1 IEC with wild-type C. albicans led to a transient increase of transepithelial electric resistance (TEER) before subsequent barrier disruption, accompanied by a strong decline of junctional protein levels and substantial, but considerably delayed cytotoxicity. Time-resolved microarray-based transcriptome analysis of C. albicans challenged IEC revealed a prominent role of NF-kappaB and MAPK signaling pathways in the response to infection. Hence, we inferred a gene regulatory network based on differentially expressed NF-kappaB and MAPK pathway components and their predicted transcriptional targets. The network model predicted activation of GDF15 by NF-kappaB was experimentally validated. Furthermore, inhibition of NF-kappaB activation in C. albicans infected C2BBe1 cells led to enhanced cytotoxicity in the epithelial cells. Taken together our study identifies NF-kappaB activation as an important protective signaling pathway in the response of epithelial cells to C. albicans. This article is protected by copyright. All rights reserved.

Authors: M. Bohringer, S. Pohlers, Sylvie Schulze, Daniela Albrecht-Eckardt, J. Piegsa, M. Weber, R. Martin, Kerstin Hünniger, Jörg Linde, Reinhard Guthke, Oliver Kurzai

Date Published: 12th Jan 2016

Journal: Cell Microbiol

Computing the various pathways of penicillin synthesis and their molar yields
FungiNet B - Bioinformatics projects

Abstract (Expand)

More than 80 years after its discovery, penicillin is still a widely used and commercially highly important antibiotic. Here, we analyse the metabolic network of penicillin synthesis in Penicillium … chrysogenum based on the concept of elementary flux modes. In particular, we consider the synthesis of the invariant molecular core of the various subtypes of penicillin and the two major ways of incorporating sulfur: transsulfuration and direct sulfhydrylation. 66 elementary modes producing this invariant core are obtained. These show four different yields with respect to glucose, notably (1/2), 2/5, 1/3, and 2/7, with the highest yield of (1/2) occurring only when direct sulfhydrylation is used and alpha-aminoadipate is completely recycled. In the case of no recycling of this intermediate, we find the maximum yield to be 2/7. We compare these values with earlier literature values. Our analysis provides a systematic overview of the redundancy in penicillin synthesis and a detailed insight into the corresponding routes. Moreover, we derive suggestions for potential knockouts that could increase the average yield.

Authors: M. T. Prausse, S. Schauble, Reinhard Guthke, Stefan Schuster

Date Published: 19th Aug 2015

Journal: Biotechnol Bioeng

Comparative proteomics of a tor inducible Aspergillus fumigatus mutant reveals involvement of the Tor kinase in iron regulation
FungiNet A - Aspergillus projects

Abstract (Expand)

The Tor (target of rapamycin) kinase is one of the major regulatory nodes in eukaryotes. Here, we analyzed the Tor kinase in Aspergillus fumigatus, which is the most important airborne fungal pathogen … of humans. Because deletion of the single tor gene was apparently lethal, we generated a conditional lethal tor mutant by replacing the endogenous tor gene by the inducible xylp-tor gene cassette. By both 2DE and gel-free LC-MS/MS, we found that Tor controls a variety of proteins involved in nutrient sensing, stress response, cell cycle progression, protein biosynthesis and degradation, but also processes in mitochondria, such as respiration and ornithine metabolism, which is required for siderophore formation. qRT-PCR analyses indicated that mRNA levels of ornithine biosynthesis genes were increased under iron limitation. When tor was repressed, iron regulation was lost. In a deletion mutant of the iron regulator HapX also carrying the xylp-tor cassette, the regulation upon iron deprivation was similar to that of the single tor inducible mutant strain. In line, hapX expression was significantly reduced when tor was repressed. Thus, Tor acts either upstream of HapX or independently of HapX as a repressor of the ornithine biosynthesis genes and thereby regulates the production of siderophores.

Authors: C. Baldin, V. Valiante, T. Kruger, L. Schafferer, H. Haas, O. Kniemeyer, Axel Brakhage

Date Published: 26th May 2015

Journal: Proteomics

Candida survival strategies
FungiNet C - Candida projects

Abstract (Expand)

Only few Candida species, e.g., Candida albicans, Candida glabrata, Candida dubliniensis, and Candida parapsilosis, are successful colonizers of a human host. Under certain circumstances these species … can cause infections ranging from superficial to life-threatening disseminated candidiasis. The success of C. albicans, the most prevalent and best studied Candida species, as both commensal and human pathogen depends on its genetic, biochemical, and morphological flexibility which facilitates adaptation to a wide range of host niches. In addition, formation of biofilms provides additional protection from adverse environmental conditions. Furthermore, in many host niches Candida cells coexist with members of the human microbiome. The resulting fungal-bacterial interactions have a major influence on the success of C. albicans as commensal and also influence disease development and outcome. In this chapter, we review the current knowledge of important survival strategies of Candida spp., focusing on fundamental fitness and virulence traits of C. albicans.

Authors: M. Polke, Bernhard Hube, Ilse Jacobsen

Date Published: 24th Feb 2015

Journal: Adv Appl Microbiol

Computational prediction of molecular pathogen-host interactions based on dual transcriptome data
FungiNet B - Bioinformatics projects, INF

Abstract (Expand)

Inference of inter-species gene regulatory networks based on gene expression data is an important computational method to predict pathogen-host interactions (PHIs). Both the experimental setup and the … nature of PHIs exhibit certain characteristics. First, besides an environmental change, the battle between pathogen and host leads to a constantly changing environment and thus complex gene expression patterns. Second, there might be a delay until one of the organisms reacts. Third, toward later time points only one organism may survive leading to missing gene expression data of the other organism. Here, we account for PHI characteristics by extending NetGenerator, a network inference tool that predicts gene regulatory networks from gene expression time series data. We tested multiple modeling scenarios regarding the stimuli functions of the interaction network based on a benchmark example. We show that modeling perturbation of a PHI network by multiple stimuli better represents the underlying biological phenomena. Furthermore, we utilized the benchmark example to test the influence of missing data points on the inference performance. Our results suggest that PHI network inference with missing data is possible, but we recommend to provide complete time series data. Finally, we extended the NetGenerator tool to incorporate gene- and time point specific variances, because complex PHIs may lead to high variance in expression data. Sample variances are directly considered in the objective function of NetGenerator and indirectly by testing the robustness of interactions based on variance dependent disturbance of gene expression values. We evaluated the method of variance incorporation on dual RNA sequencing (RNA-Seq) data of Mus musculus dendritic cells incubated with Candida albicans and proofed our method by predicting previously verified PHIs as robust interactions.

Authors: S. Schulze, S. G. Henkel, D. Driesch, R. Guthke, J. Linde

Date Published: 6th Feb 2015

Journal: Front Microbiol

Characterization of the Aspergillus fumigatus detoxification systems for reactive nitrogen intermediates and their impact on virulence
FungiNet A - Aspergillus projects

Abstract (Expand)

Aspergillus fumigatus is a saprophytic mold that can cause life-threatening infections in immunocompromised patients. In the lung, inhaled conidia are confronted with immune effector cells that attack … the fungus by various mechanisms such as phagocytosis, production of antimicrobial proteins or generation of reactive oxygen intermediates. Macrophages and neutrophils can also form nitric oxide (NO) and other reactive nitrogen intermediates (RNI) that potentially also contribute to killing of the fungus. However, fungi can produce several enzymes involved in RNI detoxification. Based on genome analysis of A. fumigatus, we identified two genes encoding flavohemoglobins, FhpA, and FhpB, which have been shown to convert NO to nitrate in other fungi, and a gene encoding S-nitrosoglutathione reductase GnoA reducing S-nitrosoglutathione to ammonium and glutathione disulphide. To elucidate the role of these enzymes in detoxification of RNI, single and double deletion mutants of FhpA, FhpB, and GnoA encoding genes were generated. The analysis of mutant strains using the NO donor DETA-NO indicated that FhpA and GnoA play the major role in defense against RNI. By generating fusions with the green fluorescence protein, we showed that both FhpA-eGFP and GnoA-eGFP were located in the cytoplasm of all A. fumigatus morphotypes, from conidia to hyphae, whereas FhpB-eGFP was localized in mitochondria. Because fhpA and gnoA mRNA was also detected in the lungs of infected mice, we investigated the role of these genes in fungal pathogenicity by using a murine infection model for invasive pulmonary aspergillosis. Remarkably, all mutant strains tested displayed wild-type pathogenicity, indicating that the ability to detoxify host-derived RNI is not essential for virulence of A. fumigatus in the applied mouse infection model. Consistently, no significant differences in killing of DeltafhpA, DeltafhpB, or DeltagnoA conidia by cells of the macrophage cell line MH-S were observed when compared to the wild type.

Authors: K. Lapp, M. Vodisch, K. Kroll, M. Strassburger, O. Kniemeyer, T. Heinekamp, Axel Brakhage

Date Published: 11th Sep 2014

Journal: Front Microbiol

Clotrimazole dampens vaginal inflammation and neutrophil infiltration in response to Candida albicans infection
FungiNet C - Candida projects

Abstract (Expand)

The pathology of vulvovaginal candidiasis (VVC) caused by Candida albicans is associated with a nonprotective inflammatory response and is frequently treated with clotrimazole. We investigated the … mechanisms by which clotrimazole resolves VVC. Low levels of clotrimazole, which do not block fungal growth, inhibit expression of a "danger response" transcription factor, c-Fos, block production of proinflammatory cytokines, and inhibit neutrophil infiltration to the site of infection.

Authors: D. Wilson, B. Hebecker, D. L. Moyes, P. Miramon, N. Jablonowski, S. Wisgott, S. Allert, J. R. Naglik, Bernhard Hube

Date Published: 29th Jul 2013

Journal: Antimicrob Agents Chemother

Comparison of transcriptome technologies in the pathogenic fungus Aspergillus fumigatus reveals novel insights into the genome and MpkA dependent gene expression
FungiNet A - Aspergillus projects, FungiNet B - Bioinformatics projects

Abstract

ABSTRACT:

Authors: Sebastian Müller, Clara Baldin, Marco Groth, Reinhard Guthke, Olaf Kniemeyer, Axel A Brakhage, Vito Valiante

Date Published: 2nd Oct 2012

Journal: BMC Genomics

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