The infectious propagules of Aspergillus fumigatus are coated with antimicrobial peptides

Abstract

Fungal spores are unique cells that mediate dispersal and survival in the environment. For pathogenic fungi encountering a susceptible host, these specialised structures may serve as infectious particles. The main causative agent of the opportunistic disease aspergillosis, Aspergillus fumigatus, produces asexual spores, the conidia, that become dissipated by air flows or water currents but also serve as propagules to infect a susceptible host. We demonstrate that the defX gene of this mould encodes putative antimicrobial peptides resembling cysteine‐stabilised (CS)αβ defensins that are expressed in a specific spatial and temporal manner in the course of asexual spore formation. Localisation studies on strains expressing a fluorescent proxy or tagged defX alleles expose that these antimicrobial peptides are secreted to coat the conidial surface. Deletion mutants reveal that the spore‐associated defX gene products delay the growth of Gram‐positive Staphylococcus aureus and demonstrate that the defX gene and presumably its encoded spore‐associated defensins confer a growth advantage to the fungal opponent over bacterial competitors. These findings have implications with respect to the ecological niche of A. fumigatus that serves as a ‘virulence school’ for this human pathogenic mould; further relevance is given for the infectious process resulting in aspergillosis, considering competition with the host microbiome or co‐infecting microorganisms to break colonisation resistance at host surfaces.

On the ecology ofAcinetobacter baumannii– jet stream rider and opportunist by nature

“…Resistance to UV radiation involves enzymes dedicated to the detoxification of reactive oxygen species (ROS) such as catalases and superoxide dismutases (101, 111), and these enzymes, ROS detoxification and thus redox homeostasis crucially determine deployment of antibiotic activity (2, 23, 39). Moreover, Aspergillus spores are coated with antimicrobial peptides (22). Adaptation to this specific niche therefore requires resistance mechanisms, which again may contribute to resistance development of A. baumannii in the hospital setting.…”

The murine lung microbiome is dysbalanced by the human pathogenic fungusAspergillus fumigatusresulting in enrichment of anaerobic bacteria

“…For example, in the lung of cystic fibrosis patients, A. fumigatus apparently shapes a lung microbiome towards a more beneficial environment for fungal growth that is associated with aromatic amino acid availability and the shikimate pathway 50 . It is conceivable that for shaping the microbiome the fungus also uses its defensin-like peptides on the conidial surface and its natural products that exhibit antimicrobial and toxic activity 49,51,52 . In the lung of mice, it was shown that A. fumigatus can produce several natural products including the toxin gliotoxin 53 .…”

“…There is evidence from in vitro experiments and in vivo analyses that A. fumigatus can modulate the microbiota [49][50][51] . For example, in the lung of cystic fibrosis patients, A. fumigatus apparently shapes a lung microbiome towards a more beneficial environment for fungal growth that is associated with aromatic amino acid availability and the shikimate pathway 50 .…”