Amoeba predation of Cryptococcus: A quantitative and population genomic evaluation of the accidental pathogen hypothesis

Fungal pathogens exhibit extensive strain heterogeneity, including variation in virulence. Whether closely related non-pathogenic species also exhibit strain heterogeneity remains unknown. Here, we comprehensively characterized the pathogenic potentials (i.e., the ability to cause morbidity and mortality) of 16 diverse strains ofAspergillus fischeri, a non-pathogenic close relative of the major pathogenAspergillus fumigatus.In vitroimmune response assays andin vivovirulence assays using a mouse model of pulmonary aspergillosis showed thatA. fischeristrains varied widely in their pathogenic potential. Furthermore, pangenome analyses suggest thatA. fischerigenomic and phenotypic diversity is even greater. Genomic, transcriptomic, and metabolomic profiling identified several pathways and secondary metabolites associated with variation in virulence. Notably, strain virulence was associated with the simultaneous presence of the secondary metabolites hexadehydroastechrome and gliotoxin. We submit that examining the pathogenic potentials of non-pathogenic close relatives is key for understanding the origins of fungal pathogenicity.

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Amoebae as training grounds for microbial pathogens

Price,

Hanford,

Al-Quadan

et al. 2024

mBio

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Grazing of amoebae on microorganisms represents one of the oldest predator-prey dynamic relationships in nature. It represents a genetic “melting pot” for an ancient and continuous multi-directional inter- and intra-kingdom horizontal gene transfer between amoebae and its preys, intracellular microbial residents, endosymbionts, and giant viruses, which has shaped the evolution, selection, and adaptation of microbes that evade degradation by predatory amoeba. Unicellular phagocytic amoebae are thought to be the ancient ancestors of macrophages with highly conserved eukaryotic processes. Selection and evolution of microbes within amoeba through their evolution to target highly conserved eukaryotic processes have facilitated the expansion of their host range to mammals, causing various infectious diseases. Legionella and environmental Chlamydia harbor an immense number of eukaryotic-like proteins that are involved in ubiquitin-related processes or are tandem repeats-containing proteins involved in protein-protein and protein-chromatin interactions. Some of these eukaryotic-like proteins exhibit novel domain architecture and novel enzymatic functions absent in mammalian cells, such as ubiquitin ligases, likely acquired from amoebae. Mammalian cells and amoebae may respond similarly to microbial factors that target highly conserved eukaryotic processes, but mammalian cells may undergo an accidental response to amoeba-adapted microbial factors. We discuss specific examples of microbes that have evolved to evade amoeba predation, including the bacterial pathogens— Legionella , Chlamydia , Coxiella, Rickettssia, Francisella, Mycobacteria , Salmonella, Bartonella , Rhodococcus , Pseudomonas, Vibrio , Helicobacter , Campylobacter , and Aliarcobacter . We also discuss the fungi Cryptococcus, and Asperigillus , as well as amoebae mimiviruses/giant viruses. We propose that amoeba-microbe interactions will continue to be a major “training ground” for the evolution, selection, adaptation, and emergence of microbial pathogens equipped with unique pathogenic tools to infect mammalian hosts. However, our progress will continue to be highly dependent on additional genomic, biochemical, and cellular data of unicellular eukaryotes.

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Amoeba predation of Cryptococcus: A quantitative and population genomic evaluation of the accidental pathogen hypothesis

Cited by 3 publications

References 88 publications

Strain heterogeneity in a non-pathogenic Aspergillus fungus highlights factors associated with virulence

Strain heterogeneity in a non-pathogenic Aspergillus fungus highlights factors associated with virulence

Strain heterogeneity in a non-pathogenic fungus highlights factors contributing to virulence

Amoebae as training grounds for microbial pathogens

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