Chitosan Biosynthesis and Virulence in the Human Fungal Pathogen Cryptococcus gattii

ABSTRACT Cryptococcus gattii R265 is a hypervirulent fungal strain responsible for the recent outbreak of cryptococcosis in Vancouver Island of British Columbia in Canada. It differs significantly from Cryptococcus neoformans in its natural environment, its preferred site in the mammalian host, and its pathogenesis. Our previous studies of C. neoformans have shown that the presence of chitosan, the deacetylated form of chitin, in the cell wall attenuates inflammatory responses in the host, while its absence induces robust immune responses, which in turn facilitate clearance of the fungus and induces a protective response. The results of the present investigation reveal that the cell wall of C. gattii R265 contains a two- to threefold larger amount of chitosan than that of C. neoformans. The genes responsible for the biosynthesis of chitosan are highly conserved in the R265 genome; the roles of the three chitin deacetylases (CDAs) have, however, been modified. To deduce their roles, single and double CDA deletion strains and a triple CDA deletion strain were constructed in a R265 background and were subjected to mammalian infection studies. Unlike C. neoformans where Cda1 has a discernible role in fungal pathogenesis, in strain R265, Cda3 is critical for virulence. Deletion of either CDA3 alone or in combination with another CDA (cda1Δ3Δ or cda2Δ3Δ) or both (cda1Δ2Δ3Δ) rendered the fungus avirulent and cleared from the infected host. Moreover, the cda1Δ2Δ3Δ strain of R265 induced a protective response to a subsequent infection with R265. These studies begin to illuminate the regulation of chitosan biosynthesis of C. gattii and its subsequent effect on fungal virulence. IMPORTANCE The fungal cell wall is an essential organelle whose components provide the first line of defense against host-induced antifungal activity. Chitosan is one of the carbohydrate polymers in the cell wall that significantly affects the outcome of host-pathogen interaction. Chitosan-deficient strains are avirulent, implicating chitosan as a critical virulence factor. C. gattii R265 is an important fungal pathogen of concern due to its ability to cause infections in individuals with no apparent immune dysfunction and an increasing geographical distribution. Characterization of the fungal cell wall and understanding the contribution of individual molecules of the cell wall matrix to fungal pathogenesis offer new therapeutic avenues for intervention. In this report, we show that the C. gattii R265 strain has evolved alternate regulation of chitosan biosynthesis under both laboratory growth conditions and during mammalian infection compared to that of C. neoformans.

Download Full-text

Chitosan biosynthesis and virulence in the human fungal pathogen Cryptococcus gattii

10.1101/759050 ◽

2019 ◽

Author(s):

Woei C. Lam ◽

Rajendra Upadhya ◽

Charles A. Specht ◽

Abigail E. Ragsdale ◽

Camaron R Hole ◽

...

Keyword(s):

Cell Wall ◽

Fungal Pathogen ◽

Cryptococcus Gattii ◽

Fungal Cell Wall ◽

Yeast Cells ◽

Fungal Pathogenesis ◽

Protective Response ◽

Fungal Cell ◽

Fungal Virulence ◽

Mammalian Infection

AbstractCryptococcus gattii R265 is a hyper-virulent fungal strain responsible for the major outbreak of cryptococcosis in Vancouver Island of British Columbia in 1999. It differs significantly from C. neoformans in its natural environment, its preferred site in the mammalian host, and in the nature and mode of pathogenesis. Our previous studies in C. neoformans have shown that the presence of chitosan, the deacetylated form of chitin, in the cell wall attenuates inflammatory responses in the host, while its absence induces robust immune responses, which in turn facilitate clearance of the fungus and induces a protective response. The results of the present investigation reveal that the cell wall of C. gattii R265 contains 2-3-fold higher amount of chitosan compared to that of C. neoformans. The genes responsible for the biosynthesis of chitosan are highly conserved in the R265 genome; the roles of the three chitin deacetylases (CDA) have however, been modified. To deduce their roles, single, double and a triple CDA deletion strains were constructed in a R265 background and were subjected to mammalian infection studies. Unlike C. neoformans where Cda1 has a discernible role in fungal pathogenesis, in R265 Cda3 is critical for virulence. Deletion of either CDA3 alone (cda3Δ) or in combination with either CDA1 (cda1Δ3Δ) or CDA2 (cda2Δ3Δ) or both (cda1Δ2Δ3Δ) rendered the yeast cells avirulent and were cleared from the infected host. Moreover, the cda1Δ2Δ3Δ strain of R265 induced a protective response to a subsequent infection with R265. These studies shed more light into the regulation of chitosan biosynthesis of C. gattii and its subsequent effect on fungal virulence.ImportanceThe fungal cell wall is an essential organelle whose components provide the first line of defense against host-induced antifungal activity. Chitosan is one of the carbohydrate polymers in the cell wall that significantly affects the outcome of host-pathogen interaction. Chitosan-deficient strains are avirulent, implicating chitosan as a critical virulence factor. C. gattii R265 is an important fungal pathogen of concern due to its ability to cause infections in individuals with no apparent immune dysfunction and an increasing geographical distribution. Characterization of the fungal cell wall and understanding the contribution of individual molecules of the cell wall matrix to fungal pathogenesis offers new therapeutic avenues for intervention. In this report, we show that the C. gattii R265 strain has evolved alternate regulation of chitosan biosynthesis under both laboratory growth conditions and during mammalian infection compared to that of C. neoformans.

Download Full-text

An Ssd1 Homolog Impacts Trehalose and Chitin Biosynthesis and Contributes to Virulence inAspergillus fumigatus

mSphere ◽

10.1128/msphere.00244-19 ◽

2019 ◽

Vol 4 (3) ◽

Cited By ~ 5

Author(s):

Arsa Thammahong ◽

Sourabh Dhingra ◽

Katherine M. Bultman ◽

Joshua D. Kerkaert ◽

Robert A. Cramer

Keyword(s):

Cell Wall ◽

Aspergillus Fumigatus ◽

Mutant Strain ◽

Filamentous Fungus ◽

Fungal Cell Wall ◽

Cell Wall Biosynthesis ◽

Null Mutant ◽

Fungal Cell ◽

Fungal Virulence ◽

Content Type

ABSTRACTRegulation of fungal cell wall biosynthesis is critical to maintain cell wall integrity in dynamic fungal infection microenvironments. Genes involved in this response that impact fungal fitness and host immune responses remain to be fully defined. In this study, we observed that a yeastssd1homolog,ssdA, in the filamentous fungusAspergillus fumigatusis involved in trehalose and cell wall homeostasis. AnssdAnull mutant strain exhibited an increase in trehalose levels and a reduction in fungal colony growth rate. In contrast, overexpression ofssdAperturbed trehalose biosynthesis and reduced germination of conidia. ThessdAnull mutant strain was more resistant to cell wall-perturbing agents, while overexpression ofssdAincreased sensitivity. Overexpression ofssdAsignificantly increased chitin levels, and both loss and overexpression ofssdAaltered subcellular localization of the class V chitin synthase CsmA. Strikingly, overexpression ofssdAabolished adherence to abiotic surfaces and severely attenuated the virulence ofA. fumigatusin a murine model of invasive pulmonary aspergillosis. Despite the severein vitrofitness defects observed upon loss ofssdA, neither surface adherence nor murine survival was impacted. In conclusion,A. fumigatusSsdA plays a critical role in cell wall homeostasis impactingA. fumigatus-host interactions.IMPORTANCEThe incidence of life-threatening infections caused by the filamentous fungusAspergillus fumigatusis increasing along with an increase in the number of fungal strains resistant to contemporary antifungal therapies. The fungal cell wall and the associated carbohydrates required for its synthesis and maintenance are attractive drug targets given that many genes encoding proteins involved in cell wall biosynthesis and integrity are absent in humans. Importantly, genes and associated cell wall biosynthesis and homeostasis regulatory pathways remain to be fully defined inA. fumigatus. In this report, we identify SsdA as an important component of trehalose and fungal cell wall biosynthesis inA. fumigatusthat consequently impacts the host immune response and fungal virulence in animal models of infection.

Download Full-text

Protein Kinase A and High-Osmolarity Glycerol Response Pathways Cooperatively Control Cell Wall Carbohydrate Mobilization inAspergillus fumigatus

mBio ◽

10.1128/mbio.01952-18 ◽

2018 ◽

Vol 9 (6) ◽

Cited By ~ 16

Author(s):

Leandro José de Assis ◽

Adriana Manfiolli ◽

Eliciane Mattos ◽

João H. T. Marilhano Fabri ◽

Iran Malavazi ◽

...

Keyword(s):

Cell Wall ◽

Protein Kinase ◽

Glycogen Synthesis ◽

Fungal Cell Wall ◽

Cell Wall Biosynthesis ◽

Fungal Cell ◽

Content Type ◽

High Osmolarity ◽

High Osmolarity Glycerol ◽

Kinase A

ABSTRACTAspergillus fumigatusmitogen-activated protein kinases (MAPKs) are involved in maintaining the normal morphology of the cell wall and providing resistance against cell wall-damaging agents. Upon cell wall stress, cell wall-related sugars need to be synthesized from carbohydrate storage compounds. Here we show that this process is dependent on cAMP-dependent protein kinase A (PKA) activity and regulated by the high-osmolarity glycerol response (HOG) MAPKs SakA and MpkC. These protein kinases are necessary for normal accumulation/degradation of trehalose and glycogen, and the lack of these genes reduces glucose uptake and glycogen synthesis. Alterations in glycogen synthesis were observed for thesakAandmpkCdeletion mutants, which also displayed alterations in carbohydrate exposure on the cell wall. Carbohydrate mobilization is controlled by SakA interaction with PkaC1 and PkaR, suggesting a putative mechanism where the PkaR regulatory subunit leaves the complex and releases the SakA-PkaC1 complex for activation of enzymes involved in carbohydrate mobilization. This work reveals the communication between the HOG and PKA pathways for carbohydrate mobilization for cell wall construction.IMPORTANCEAspergillus fumigatusis an opportunistic human pathogen causing allergic reactions or systemic infections such as invasive pulmonary aspergillosis, especially in immunocompromised patients. The fungal cell wall is the main component responsible for recognition by the immune system, due to the specific composition of polysaccharide carbohydrates exposed on the surface of the fungal cell wall called pathogen-associated molecular patterns (PAMPs). Key enzymes in the fungal cell wall biosynthesis are a good target for fungal drug development. This report elucidates the cooperation between the HOG and PKA pathways in the mobilization of carbohydrates for fungal cell wall biosynthesis. We suggest that the reduced mobilization of simple sugars causes defects in the structure of the fungal cell wall. In summary, we propose that SakA is important for PKA activity, therefore regulating the availability and mobilization of monosaccharides for fungal cell wall biosynthesis during cell wall damage and the osmotic stress response.

Download Full-text

Identification of Genes Involved in the Synthesis of the Fungal Cell Wall Component Nigeran and Regulation of Its Polymerization in Aspergillus luchuensis

Applied and Environmental Microbiology ◽

10.1128/aem.01144-21 ◽

2021 ◽

Vol 87 (21) ◽

Author(s):

Keiko Uechi ◽

Hajime Yaguchi ◽

Jikian Tokashiki ◽

Toki Taira ◽

Osamu Mizutani

Keyword(s):

Cell Wall ◽

Fungal Cell Wall ◽

Cell Wall Polysaccharide ◽

Cell Wall Component ◽

Fungal Cell ◽

Content Type ◽

Aspergillus Luchuensis

The fungal cell wall is composed mainly of polysaccharides. Under nitrogen-free conditions, some Aspergillus and Penicillium spp. produce significant levels of nigeran, a fungal cell wall polysaccharide composed of alternating α-1,3/1,4-glucosidic linkages.

Download Full-text

The Glycosylphosphatidylinositol-Anchored DFG Family Is Essential for the Insertion of Galactomannan into the β-(1,3)-Glucan–Chitin Core of the Cell Wall of Aspergillus fumigatus

mSphere ◽

10.1128/msphere.00397-19 ◽

2019 ◽

Vol 4 (4) ◽

Cited By ~ 7

Author(s):

Laetitia Muszkieta ◽

Thierry Fontaine ◽

Rémi Beau ◽

Isabelle Mouyna ◽

Marian Samuel Vogt ◽

...

Keyword(s):

Cell Wall ◽

Aspergillus Fumigatus ◽

Gene Family ◽

Protein Complexes ◽

Growth Conditions ◽

Fungal Cell Wall ◽

Cross Linking ◽

Fungal Cell ◽

Content Type

ABSTRACT The fungal cell wall is a complex and dynamic entity essential for the development of fungi. It is composed mainly of polysaccharides that are synthetized by protein complexes. At the cell wall level, enzyme activities are involved in postsynthesis polysaccharide modifications such as cleavage, elongation, branching, and cross-linking. Glycosylphosphatidylinositol (GPI)-anchored proteins have been shown to participate in cell wall biosynthesis and specifically in polysaccharide remodeling. Among these proteins, the DFG family plays an essential role in controlling polar growth in yeast. In the filamentous fungus and opportunistic human pathogen Aspergillus fumigatus, the DFG gene family contains seven orthologous DFG genes among which only six are expressed under in vitro growth conditions. Deletions of single DFG genes revealed that DFG3 plays the most important morphogenetic role in this gene family. A sextuple-deletion mutant resulting from the deletion of all in vitro expressed DFG genes did not contain galactomannan in the cell wall and has severe growth defects. This study has shown that DFG members are absolutely necessary for the insertion of galactomannan into the cell wall of A. fumigatus and that the proper cell wall localization of the galactomannan is essential for correct fungal morphogenesis in A. fumigatus. IMPORTANCE The fungal cell wall is a complex and dynamic entity essential for the development of fungi. It is composed mainly of polysaccharides that are synthetized by protein complexes. Enzymes involved in postsynthesis polysaccharide modifications, such as cleavage, elongation, branching, and cross-linking, are essential for fungal life. Here, we investigated in Aspergillus fumigatus the role of the members of the Dfg family, one of the 4 GPI-anchored protein families common to yeast and molds involved in cell wall remodeling. Molecular and biochemical approaches showed that DFG members are required for filamentous growth, conidiation, and cell wall organization and are essential for the life of this fungal pathogen.

Download Full-text

Species in the Cryptococcus gattii Complex Differ in Capsule and Cell Size following Growth under Capsule-Inducing Conditions

mSphere ◽

10.1128/msphere.00350-16 ◽

2016 ◽

Vol 1 (6) ◽

Cited By ~ 15

Author(s):

Kenya E. Fernandes ◽

Christine Dwyer ◽

Leona T. Campbell ◽

Dee A. Carter

Keyword(s):

Cell Wall ◽

New Species ◽

Cell Size ◽

Fungal Pathogen ◽

Species Complex ◽

Cryptococcus Gattii ◽

Clinical Infection ◽

Content Type ◽

Diagnosis And Prognosis ◽

Capsule Size

ABSTRACT Infections with the fungal pathogen Cryptococcus gattii have been increasing in recent years. Recently, four different species have been described within C. gattii, which correspond to four previously known molecular genotypes (VGI to VGIV). Examining traits related to infection and disease is important for determining whether these different species have clinical relevance. This study examined variation in attributes that are important for infecting and surviving in the host, including tolerance to various stresses, yeast cell size, and the amount of polysaccharide capsule that covers the cell. The cell size and capsule size were significantly different and inversely correlated across the species. Thermotolerance was highest in C. deuterogattii (VGII), the only species known to cause outbreaks, while most strains of the species C. bacillisporus (VGIII) and C. tetragattii (VGIV) grew poorly at 37°C. These findings argue for increased acceptance of the new species and may be useful for informing diagnosis and prognosis in clinical infection. Cryptococcus gattii causes invasive fungal infections that have been increasing in incidence and global distribution in recent years. The major molecular genotypes of C. gattii that were previously classified as VGI to VGIV have recently been described as four new species: C. gattii (VGI), C. deuterogattii (VGII), C. bacillisporus (VGIII), and C. tetragattii (VGIV). The main driver for their classification has been phylogeny, and phenotypic diversity has not yet been extensively characterized. This study examines variation in attributes related to virulence and pathogenicity, including capsule thickness, cell size, tolerance to temperature, oxidative and osmotic stress, and cell wall integrity. A capsule induction agar using diluted Sabouraud medium revealed significant differences in capsule and cell size across the C. gattii species complex and produced irregularly shaped elongated cells in a number of strains. C. gattii/VGI strains possessed the largest capsules of all species but had smaller cells, while C. deuterogattii/VGII strains possessed the largest cells of all species but had smaller capsules. Overall thermotolerance was highest in C. deuterogattii/VGII strains, while a number of C. bacillisporus/VGIII, and C. tetragattii/VGIV strains had substantially reduced growth at 37°C. There was no significant difference among species in their tolerances to oxidative or osmotic stresses, and there was no evidence for defects in cell wall integrity in strains producing irregular cells. These data support the division of the C. gattii species complex into distinctly identified species and suggest underlying reasons for their differences in virulence, epidemiology, and host preference. IMPORTANCE Infections with the fungal pathogen Cryptococcus gattii have been increasing in recent years. Recently, four different species have been described within C. gattii, which correspond to four previously known molecular genotypes (VGI to VGIV). Examining traits related to infection and disease is important for determining whether these different species have clinical relevance. This study examined variation in attributes that are important for infecting and surviving in the host, including tolerance to various stresses, yeast cell size, and the amount of polysaccharide capsule that covers the cell. The cell size and capsule size were significantly different and inversely correlated across the species. Thermotolerance was highest in C. deuterogattii (VGII), the only species known to cause outbreaks, while most strains of the species C. bacillisporus (VGIII) and C. tetragattii (VGIV) grew poorly at 37°C. These findings argue for increased acceptance of the new species and may be useful for informing diagnosis and prognosis in clinical infection.

Download Full-text

Two KTR Mannosyltransferases Are Responsible for the Biosynthesis of Cell Wall Mannans and Control Polarized Growth inAspergillus fumigatus

mBio ◽

10.1128/mbio.02647-18 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 13

Author(s):

Christine Henry ◽

Jizhou Li ◽

François Danion ◽

Laura Alcazar-Fuoli ◽

Emilia Mellado ◽

...

Keyword(s):

Cell Wall ◽

Invasive Aspergillosis ◽

Aspergillus Fumigatus ◽

Filamentous Fungi ◽

Biosynthetic Pathway ◽

Fungal Cell Wall ◽

Polarized Growth ◽

Biological Functions ◽

Fungal Cell ◽

Content Type

ABSTRACTFungal cell wall mannans are complex carbohydrate polysaccharides with different structures in yeasts and molds. In contrast to yeasts, their biosynthetic pathway has been poorly investigated in filamentous fungi. InAspergillus fumigatus, the major mannan structure is a galactomannan that is cross-linked to the β-1,3-glucan-chitin cell wall core. This polymer is composed of a linear mannan with a repeating unit composed of four α1,6-linked and α1,2-linked mannoses with side chains of galactofuran. Despite its use as a biomarker to diagnose invasive aspergillosis, its biosynthesis and biological function were unknown. Here, we have investigated the function of three members of the Ktr (also named Kre2/Mnt1) family (Ktr1, Ktr4, and Ktr7) inA. fumigatusand show that two of them are required for the biosynthesis of galactomannan. In particular, we describe a newly discovered form of α-1,2-mannosyltransferase activity encoded by theKTR4gene. Biochemical analyses showed that deletion of theKTR4gene or theKTR7gene leads to the absence of cell wall galactomannan. In comparison to parental strains, theΔktr4andΔktr7mutants showed a severe growth phenotype with defects in polarized growth and in conidiation, marked alteration of the conidial viability, and reduced virulence in a mouse model of invasive aspergillosis. In yeast, the KTR proteins are involved in protein 0- and N-glycosylation. This study provided another confirmation that orthologous genes can code for proteins that have very different biological functions in yeasts and filamentous fungi. Moreover, inA. fumigatus, cell wall mannans are as important structurally as β-glucans and chitin.IMPORTANCEThe fungal cell wall is a complex and dynamic entity essential for the development of fungi. It allows fungal pathogens to survive environmental challenge posed by nutrient stress and host defenses, and it also is central to polarized growth. The cell wall is mainly composed of polysaccharides organized in a three-dimensional network.Aspergillus fumigatusproduces a cell wall galactomannan whose biosynthetic pathway and biological functions remain poorly defined. Here, we described two new mannosyltransferases essential to the synthesis of the cell wall galactomannan. Their absence leads to a growth defect with misregulation of polarization and altered conidiation, with conidia which are bigger and more permeable than the conidia of the parental strain. This study showed that in spite of its low concentration in the cell wall, this polysaccharide is absolutely required for cell wall stability, for apical growth, and for the full virulence ofA. fumigatus.

Download Full-text

Cryptococcus neoformansCda1 and Its Chitin Deacetylase Activity Are Required for Fungal Pathogenesis

mBio ◽

10.1128/mbio.02087-18 ◽

2018 ◽

Vol 9 (6) ◽

Cited By ~ 24

Author(s):

Rajendra Upadhya ◽

Lorina G. Baker ◽

Woei C. Lam ◽

Charles A. Specht ◽

Maureen J. Donlin ◽

...

Keyword(s):

Cell Wall ◽

Cryptococcus Neoformans ◽

Fungal Pathogenesis ◽

Mammalian Host ◽

Infection Model ◽

Chitin Deacetylase ◽

Fungal Cell ◽

Content Type ◽

Mutant Strains

ABSTRACTChitin is an essential component of the cell wall ofCryptococcus neoformansconferring structural rigidity and integrity under diverse environmental conditions. Chitin deacetylase genes encode the enyzmes (chitin deacetylases [Cdas]) that deacetylate chitin, converting it to chitosan. The functional role of chitosan in the fungal cell wall is not well defined, but it is an important virulence determinant ofC. neoformans. Mutant strains deficient in chitosan are completely avirulent in a mouse pulmonary infection model.C. neoformanscarries genes that encode three Cdas (Cda1, Cda2, and Cda3) that appear to be functionally redundant in cells grown under vegetative conditions. Here we report thatC. neoformansCda1 is the principal Cda responsible for fungal pathogenesis. Point mutations were introduced in the active site of Cda1 to generate strains in which the enzyme activity of Cda1 was abolished without perturbing either its stability or localization. When used to infect CBA/J mice, Cda1 mutant strains produced less chitosan and were attenuated for virulence. We further demonstrate thatC. neoformansCda genes are transcribed differently during a murine infection from what has been measuredin vitro.IMPORTANCECryptococcus neoformansis unique among fungal pathogens that cause disease in a mammalian host, as it secretes a polysaccharide capsule that hinders recognition by the host to facilitate its survival and proliferation. Even though it causes serious infections in immunocompromised hosts, reports of infection in hosts that are immunocompetent are on the rise. The cell wall of a fungal pathogen, its synthesis, composition, and pathways of remodelling are attractive therapeutic targets for the development of fungicides. Chitosan, a polysaccharide in the cell wall ofC. neoformansis one such target, as it is critical for pathogenesis and absent in the host. The results we present shed light on the importance of one of the chitin deacetylases that synthesize chitosan during infection and further implicates chitosan as being a critical factor for the pathogenesis ofC. neoformans.

Download Full-text

Potential of Chemically Synthesized Oligosaccharides To Define the Carbohydrate Moieties of the Fungal Cell Wall Responsible for the Human Immune Response, Using Aspergillus fumigatus Galactomannan as a Model

mSphere ◽

10.1128/msphere.00688-19 ◽

2020 ◽

Vol 5 (1) ◽

Cited By ~ 8

Author(s):

Sarah Sze Wah Wong ◽

Vadim B. Krylov ◽

Dmitry A. Argunov ◽

Alexander A. Karelin ◽

Jean-Phillipe Bouchara ◽

...

Keyword(s):

Immune Response ◽

Cell Wall ◽

Aspergillus Fumigatus ◽

Fungal Cell Wall ◽

Human Pathogens ◽

Cell Wall Polysaccharides ◽

Fungal Cell ◽

Content Type ◽

Human Immune Response ◽

Synthetic Oligosaccharides

ABSTRACT Methodologies to identify epitopes or ligands of the fungal cell wall polysaccharides influencing the immune response of human pathogens have to date been imperfect. Using the galactomannan (GM) of Aspergillus fumigatus as a model, we have shown that synthetic oligosaccharides of distinct structures representing key fragments of cell wall polysaccharides are the most precise tools to study the serological and immunomodulatory properties of a fungal polysaccharide.

Download Full-text

A Ssd1 homolog impacts trehalose and chitin biosynthesis and contributes to virulence inAspergillus fumigatus

10.1101/594341 ◽

2019 ◽

Author(s):

Arsa Thammahong ◽

Sourabh Dhingra ◽

Katherine M. Bultman ◽

Joshua Kerkaert ◽

Robert A. Cramer

Keyword(s):

Cell Wall ◽

Aspergillus Fumigatus ◽

Mutant Strain ◽

Filamentous Fungus ◽

Fungal Cell Wall ◽

Cell Wall Biosynthesis ◽

Null Mutant ◽

Fungal Cell ◽

Fungal Virulence ◽

Over Expression

AbstractRegulation of fungal cell wall biosynthesis is critical to maintain cell wall integrity in the face of dynamic fungal infection microenvironments. In this study, we observe that a yeastssd1homolog,ssdA,in the filamentous fungusAspergillus fumigatusis involved in trehalose and cell wall homeostasis. AnssdAnull mutant strain exhibited an increase in trehalose levels and a reduction in colony growth rate. Over-expression ofssdAin contrast perturbed trehalose biosynthesis and reduced conidia germination rates. ThessdAnull mutant strain was more resistant to cell wall perturbing agents while over-expression ofssdApromoted increased sensitivity. Over-expression ofssdAsignificantly increased chitin levels and both loss and over-expression ofssdAaltered sub-cellular localization of the class V chitin synthase CsmA. Strikingly, over-expression ofssdAabolished adherence to abiotic surfaces and severely attenuated the virulence ofA. fumigatusin a murine model of invasive pulmonary aspergillosis. In contrast, despite the severein vitrofitness defects observed upon loss ofssdA,neither surface adherence or murine survival was impacted. In conclusion,A. fumigatusSsdA plays a critical role in cell wall homeostasis that alters fungal-host interactions.ImportanceLife threatening infections caused by the filamentous fungusAspergillus fumigatusare increasing along with a rise in fungal strains resistant to contemporary antifungal therapies. The fungal cell wall and the associated carbohydrates required for its synthesis and maintenance are attractive drug targets given that many genes encoding proteins involved in cell wall biosynthesis and integrity are absent in humans. Importantly, genes and associated cell wall biosynthesis and homeostasis regulatory pathways remain to be fully defined inA. fumigatus.In this study, we identify SsdA, a model yeast Ssd1p homolog, as an important component of trehalose and fungal cell wall biosynthesis inA. fumigatusthat consequently impacts fungal virulence in animal models of infection.

Download Full-text