Summary Size and diverse morphologies pose a primary challenge for phagocytes such as innate immune cells and predatory amoebae when encountering fungal prey. Although filamentous fungi can escape phagocytic killing by pure physical constraints, unicellular spores and yeasts can mask molecular surface patterns or arrest phagocytic processing. Here, we show that the fungivorous amoeba Protostelium aurantium was able to adjust its killing and feeding mechanisms to these different cell shapes. Yeast‐like fungi from the major fungal groups of basidiomycetes and ascomycetes were readily internalized by phagocytosis, except for the human pathogen Candida albicans whose mannoprotein coat was essential to escape recognition by the amoeba. Dormant spores of the filamentous fungus Aspergillus fumigatus also remained unrecognized, but swelling and the onset of germination induced internalization and intracellular killing by the amoeba. Mature hyphae of A. fumigatus were mostly attacked from the hyphal tip and killed by an actin‐mediated invasion of fungal filaments. Our results demonstrate that predatory pressure imposed by amoebae in natural environments selects for distinct survival strategies in yeast and filamentous fungi but commonly targets the fungal cell wall as a crucial molecular pattern associated to prey and pathogens.

Intestinal microbiota dysbiosis can initiate overgrowth of commensal Candida species – a major predisposing factor for disseminated candidiasis. Commensal bacteria such as Lactobacillus rhamnosus can antagonize Candida albicans pathogenicity. Here, we investigate the interplay between C. albicans, L. rhamnosus, and intestinal epithelial cells by integrating transcriptional and metabolic profiling, and reverse genetics. Untargeted metabolomics and in silico modelling indicate that intestinal epithelial cells foster bacterial growth metabolically, leading to bacterial production of antivirulence compounds. In addition, bacterial growth modifies the metabolic environment, including removal of C. albicans’ favoured nutrient sources. This is accompanied by transcriptional and metabolic changes in C. albicans, including altered expression of virulence-related genes. Our results indicate that intestinal colonization with bacteria can antagonize C. albicans by reshaping the metabolic environment, forcing metabolic adaptations that reduce fungal pathogenicity.

Hypervalent iodine reagents have recently emerged as powerful tools for late-stage peptide and protein functionalization. Herein we report a tyrosine bioconjugation methodology for the introduction of hypervalent iodine onto biomolecules...

Candida species are the most prevalent cause of invasive fungal infections, of which Candida albicans is the most common. Translocation across the epithelial barrier into the bloodstream by intestinal-colonizing C. albicans cells serves as the main source for systemic infections. Understanding the fungal mechanisms behind this process will give valuable insights on how to prevent such infections and keep C. albicans in the commensal state in patients with predisposing conditions. This review will focus on recent developments in characterizing fungal translocation mechanisms, compare what we know about enteric bacterial pathogens with C. albicans , and discuss the different proposed hypotheses for how C. albicans enters and disseminates through the bloodstream immediately following translocation.

Predatory interactions among microbes are major evolutionary driving forces for biodiversity. The fungivorous amoeba Protostelium aurantium has a wide fungal food spectrum including foremost pathogenic members of the genus Candida. Here we show that upon phagocytic ingestion by the amoeba, Candida parapsilosis is confronted with an oxidative burst and undergoes lysis within minutes of processing in acidified phagolysosomes. On the fungal side, a functional genomic approach identified copper and redox homeostasis as primary targets of amoeba predation, with the highly expressed copper exporter gene CRP1 and the peroxiredoxin gene PRX1 contributing to survival when encountered with P. aurantium. The fungicidal activity was largely retained in intracellular vesicles of the amoebae. Following their isolation, the content of these vesicles induced immediate killing and lysis of C. parapsilosis in vitro.Proteomic analysis identified 56 vesicular proteins from P. aurantium. Although completely unknown proteins were dominant, many of them could be categorised as hydrolytic enzymes targeting the fungal cell wall, indicating that fungal cell wall structures are under selection pressure by predatory phagocytes in natural environments. Take Away• The amoeba Protostelium aurantium feeds on fungi, such as Candida parapsilosis.• Ingested yeast cells are exposed to reactive oxygen species.• A copper exporter and a peroxiredoxin contribute to fungal defence.

Poster session 1, September 21, 2022, 12:30 PM - 1:30 PM Fungal infections represent a serious burden on human health. Increasing numbers of susceptible hosts, a limited set of approved antifungal drugs which frequently trigger undesired side effects, and the emergence of resistant strains highlight the urgent demand for novel antifungal drug formulations. However, the biological similarity of human and fungal cells hampers the development of new antifungals which do not also harm humans. In nature, organisms in almost all domains of life produce antimicrobial peptides to combat microbial pathogens. Those peptides share certain characteristics, such as being short, amphiphilic molecules with a positive net charge.1 We designed synthetic polyacrylamides which mimic the properties of naturally occurring antifungal peptides. These positively charged, amphiphilic polymers are advantageous over peptides because of their easy synthesis and stability against proteases. Initial structure-activity relationship studies revealed an optimal cLogP (the calculated hydrophobicity of a molecule) around 1.5 to ensure activity against C. albicans and simultaneous biocompatibility with host cells.2 Additionally, shorter polymers with a length of 20 subunits were more effective than their longer versions.2 In terms of their therapeutic index, certain compositions outperformed the broad-spectrum antifungal amphotericin B and were even effective against drug-resistant clinical isolates of C. albicans.2 Candida albicans strains with known antifungal drug-resistance mutations were not affected in their susceptibility to the polymers. Therefore, investigations were carried out to elucidate the mode of action of the polymers. The transcriptome of C. albicans cells treated with subinhibitory concentrations of the polymers revealed an increased expression of genes involved in general stress response and upregulation in protein processing in the endoplasmic reticulum, particularly glycosylation and degradation. These findings, together with electron microscopy observations, indicated damage to the mannoproteins in the cell wall of the fungus. Membrane damage was also observed utilizing a C. albicans strain expressing GFP intracellularly. The in vitro therapeutic potential of the most promising polymer was tested in a human epithelial cell (HEC) model simulating C. albicans infection. The polymer alone was not able to prevent C. albicans infection of HECs. However, the combination of polymer with caspofungin or fluconazole showed very strong synergistic effects at otherwise non-inhibitory concentrations of the individual antifungals, successfully stopping fungal infection in vitro without damaging the HECs. These results underline the potential of synthetic polymers as an alternative treatment for fungal infections with low toxicity to human cells and a novel mode of action. Sources: 1. Fernández de Ullivarri, M., Arbulu, S., Garcia-Gutierrez, E. and Cotter, P.D. Antifungal peptides as therapeutic agents. Front Cell Infect Microbiol 10, 00 105 (2020). 2. Schaefer, S. et al. Rational design of an antifungal polyacrylamide library with reduced host-cell toxicity. ACS Appl Mater Interfaces 13, 27430-27444 (2021).

Correction for ‘Tyrosine bioconjugation with hypervalent iodine’ by Nina Declas et al., Chem. Sci., 2022, 13, 12808–12817, https://doi.org/10.1039/D2SC04558C.

Hypervalent iodine reagents have recently emerged as powerful tools for late-stage peptide and protein functionalization. Herein we report a tyrosine bioconjugation methodology for the introduction of hypervalent iodine onto biomolecules under physiological conditions. Tyrosine residues were engaged in a selective addition onto the alkynyl bond of ethynylbenziodoxolones (EBX), resulting in stable vinylbenziodoxolones (VBX) bioconjugates. The methodology was successfully applied to peptides and proteins and tolerated all other nucleophilic residues, with the exception of cysteine. The generated VBX were further functionalized by palladium-catalyzed cross-coupling and azide-alkyne cycloaddition reactions. The method could be successfully used to modify bioactive natural products and native streptavidin to enable thiol-mediated cellular uptake.