Cell Wall-Associated Virulence Factors Contribute to Increased Resilience of Old Cryptococcus neoformans Cells

ABSTRACTBacteria interact with each other in nature and often compete for limited nutrient and space resources. However, it is largely unknown whether and how bacteria also interact with human fungal pathogens naturally found in the environment. Here, we identified a soil bacterium,Bacillus safensis, which potently blocked several keyCryptococcus neoformansvirulence factors, including formation of the antioxidant pigment melanin and production of the antiphagocytic polysaccharide capsule. The bacterium also inhibitedde novocryptococcal biofilm formation but had only modest inhibitory effects on already formed biofilms or planktonic cell growth. The inhibition of fungal melanization was dependent on direct cell contact and live bacteria.B. safensisalso had anti-virulence factor activity against another major human-associated fungal pathogen,Candida albicans. Specifically, dual-species interaction studies revealed that the bacterium strongly inhibitedC. albicansfilamentation and biofilm formation. In particular,B. safensisphysically attached to and degraded candidal filaments. Through genetic and phenotypic analyses, we demonstrated that bacterial chitinase activity against fungal cell wall chitin is a factor contributing to the antipathogen effect ofB. safensis.IMPORTANCEPathogenic fungi are estimated to contribute to as many human deaths as tuberculosis or malaria. Two of the most common fungal pathogens,Cryptococcus neoformansandCandida albicans, account for up to 1.4 million infections per year with very high mortality rates. Few antifungal drugs are available for treatment, and development of novel therapies is complicated by the need for pathogen-specific targets. Therefore, there is an urgent need to identify novel drug targets and new drugs. Pathogens use virulence factors during infection, and it has recently been proposed that targeting these factors instead of the pathogen itself may represent a new approach to develop antimicrobials. Here, we identified a soil bacterium that specifically blocked virulence factor production and biofilm formation byC. neoformansandC. albicans. We demonstrate that the bacterial antipathogen mechanism is based in part on targeting the fungal cell wall, a structure not found in human cells.

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UGD1, Encoding the Cryptococcus neoformans UDP-Glucose Dehydrogenase, Is Essential for Growth at 37°C and for Capsule Biosynthesis

Eukaryotic Cell ◽

10.1128/ec.3.6.1601-1608.2004 ◽

2004 ◽

Vol 3 (6) ◽

pp. 1601-1608 ◽

Cited By ~ 49

Author(s):

Frédérique Moyrand ◽

Guilhem Janbon

Keyword(s):

Cell Wall ◽

Sodium Dodecyl Sulfate ◽

Cryptococcus Neoformans ◽

Virulence Factors ◽

Biosynthetic Pathway ◽

Glucuronic Acid ◽

Glucose Dehydrogenase ◽

Sodium Dodecyl ◽

Gene Encoding ◽

Common Cell

ABSTRACT We report the identification and disruption of the Cryptococcus neoformans var. grubii UGD1 gene encoding the UDP-glucose dehydrogenase, which catalyzes the conversion of UDP-glucose into UDP-glucuronic acid. Deletion of UGD1 led to modifications in the cell wall, as revealed by changes in the sensitivity of ugd1Δ cells to sodium dodecyl sulfate, NaCl, and sorbitol. Moreover, two of the yeast's major virulence factors—capsule biosynthesis and the ability to grow at 37°C—were impaired in ugd1Δ strains. These results suggest that the UDP-dehydrogenase represents the major, and maybe only, biosynthetic pathway for UDP-glucuronic acid in C. neoformans. Consequently, deletion of UGD1 blocked not only the synthesis of UDP-glucuronic acid but also that of UDP-xylose. To differentiate the phenotype(s) associated with the UDP-glucuronic acid defect alone from those linked to the UDP-xylose defect, ugd1Δ mutants were phenotypically compared to strains from which the gene encoding UDP-xylose synthase (i.e., that required for synthesis of UDP-xylose) had been deleted. Finally, studies of strains from which one of the four CAP genes (CAP10, CAP59, CAP60, or CAP64) had been deleted revealed common cell wall phenotypes associated with the acapsular state.

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Faculty Opinions recommendation of Vesicular polysaccharide export in Cryptococcus neoformans is a eukaryotic solution to the problem of fungal trans-cell wall transport.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1057947.509889 ◽

2007 ◽

Author(s):

Herb Arst

Keyword(s):

Cell Wall ◽

Cryptococcus Neoformans

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Faculty Opinions recommendation of Cryptococcus neoformans Rim101 is associated with cell wall remodeling and evasion of the host immune responses.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.717972259.793469838 ◽

2013 ◽

Author(s):

June Kwon-Chung

Keyword(s):

Cell Wall ◽

Immune Responses ◽

Cryptococcus Neoformans ◽

Host Immune Responses ◽

Cell Wall Remodeling

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Bacterial Quorum-Quenching Lactonase Hydrolyzes Fungal Mycotoxin and Reduces Pathogenicity of Penicillium expansum—Suggesting a Mechanism of Bacterial Antagonism

Journal of Fungi ◽

10.3390/jof7100826 ◽

2021 ◽

Vol 7 (10) ◽

pp. 826

Author(s):

Shlomit Dor ◽

Dov Prusky ◽

Livnat Afriat-Jurnou

Keyword(s):

Cell Wall ◽

Quorum Sensing ◽

Virulence Factors ◽

Molecular Mechanisms ◽

Recombinant Expression ◽

Bacterial Species ◽

Quorum Quenching ◽

Host Cells ◽

Penicillium Expansum ◽

Fungal Colonization

Penicillium expansum is a necrotrophic wound fungal pathogen that secrets virulence factors to kill host cells including cell wall degrading enzymes (CWDEs), proteases, and mycotoxins such as patulin. During the interaction between P. expansum and its fruit host, these virulence factors are strictly modulated by intrinsic regulators and extrinsic environmental factors. In recent years, there has been a rapid increase in research on the molecular mechanisms of pathogenicity in P. expansum; however, less is known regarding the bacteria–fungal communication in the fruit environment that may affect pathogenicity. Many bacterial species use quorum-sensing (QS), a population density-dependent regulatory mechanism, to modulate the secretion of quorum-sensing signaling molecules (QSMs) as a method to control pathogenicity. N-acyl homoserine lactones (AHLs) are Gram-negative QSMs. Therefore, QS is considered an antivirulence target, and enzymes degrading these QSMs, named quorum-quenching enzymes, have potential antimicrobial properties. Here, we demonstrate that a bacterial AHL lactonase can also efficiently degrade a fungal mycotoxin. The mycotoxin is a lactone, patulin secreted by fungi such as P. expansum. The bacterial lactonase hydrolyzed patulin at high catalytic efficiency, with a kcat value of 0.724 ± 0.077 s−1 and KM value of 116 ± 33.98 μM. The calculated specific activity (kcat/KM) showed a value of 6.21 × 103 s−1M−1. While the incubation of P. expansum spores with the purified lactonase did not inhibit spore germination, it inhibited colonization by the pathogen in apples. Furthermore, adding the purified enzyme to P. expansum culture before infecting apples resulted in reduced expression of genes involved in patulin biosynthesis and fungal cell wall biosynthesis. Some AHL-secreting bacteria also express AHL lactonase. Here, phylogenetic and structural analysis was used to identify putative lactonase in P. expansum. Furthermore, following recombinant expression and purification of the newly identified fungal enzyme, its activity with patulin was verified. These results indicate a possible role for patulin and lactonases in inter-kingdom communication between fungi and bacteria involved in fungal colonization and antagonism and suggest that QQ lactonases can be used as potential antifungal post-harvest treatment.

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Screening and Antifungal Activity of a β-Carboline Derivative against Cryptococcus neoformans and C. gattii

International Journal of Microbiology ◽

10.1155/2019/7157845 ◽

2019 ◽

Vol 2019 ◽

pp. 1-8 ◽

Cited By ~ 1

Author(s):

Kátia Santana Cruz ◽

Emerson Silva Lima ◽

Marcia de Jesus Amazonas da Silva ◽

Erica Simplício de Souza ◽

Andreia Montoia ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Antifungal Activity ◽

Cryptococcus Neoformans ◽

Active Compound ◽

Cell Walls ◽

Human Fibroblasts ◽

Lead Compound ◽

Fungal Cell ◽

Fungal Cell Walls

Background. Cryptococcosis is a fungal disease of bad prognosis due to its pathogenicity and the toxicity of the drugs used for its treatment. The aim of this study was to investigate the medicinal potential of carbazole and β-carboline alkaloids and derivatives against Cryptococcus neoformans and C. gattii. Methods. MICs were established in accordance with the recommendations of the Clinical and Laboratory Standards Institute for alkaloids and derivatives against C. neoformans and C. gattii genotypes VNI and VGI, respectively. A single active compound was further evaluated against C. neoformans genotypes VNII, VNIII, and VNIV, C. gattii genotypes VGI, VGIII, and VGIV, Candida albicans ATCC 36232, for cytotoxicity against the MRC-5 lineage of human fibroblasts and for effects on fungal cells (cell wall, ergosterol, and leakage of nucleic acids). Results. Screening of 11 compounds revealed 8-nitroharmane as a significant inhibitor (MIC 40 μg/mL) of several C. neoformans and C. gattii genotypes. It was not toxic to fibroblasts (IC50 > 50 µg/mL) nor did it alter fungal cell walls or the concentration of ergosterol in C. albicans or C. neoformans. It increased leakage of substances that absorb at 260 nm. Conclusions. The synthetic β-carboline 8-nitroharmane significantly inhibits pathogenic Cryptococcus species and is interesting as a lead compound towards new therapy for Cryptococcus infections.

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Laccase Expression in Murine Pulmonary Cryptococcus neoformans Infection

Infection and Immunity ◽

10.1128/iai.73.5.3124-3127.2005 ◽

2005 ◽

Vol 73 (5) ◽

pp. 3124-3127 ◽

Cited By ~ 16

Author(s):

Javier Garcia-Rivera ◽

Stephanie C. Tucker ◽

Marta Feldmesser ◽

Peter R. Williamson ◽

Arturo Casadevall

Keyword(s):

Electron Microscopy ◽

Cell Wall ◽

Cryptococcus Neoformans ◽

Lung Tissue ◽

Immunogold Electron Microscopy ◽

Cell Cytoplasm ◽

Fungal Cell ◽

Time Of Infection

ABSTRACT Cryptococcus neoformans laccase expression during murine infection was investigated in lung tissue by immunohistochemistry and immunogold electron microscopy. Laccase was detected in the fungal cell cytoplasm, cell wall, and capsule in vivo. The amount of laccase found in different sites varied as a function of the time of infection.

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