The fungivorous amoeba Protostelium aurantium targets redox homeostasis and cell wall integrity during intracellular killing of Candida parapsilosis

Abstract

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.

Adaptation to an amoeba host drives selection of virulence-associated traits and genetic variation in saprotrophic Candida albicans

“…Additionally, resistance to oxidative stress in the C. albicans -exposed isolate appears to be activated by both amoebae and oxidative stress. Our results are consistent with the study on the interaction between C. albicans , C. parapsilosis, C. glabrata with P. aurantium ( Radosa et al., 2021 ). Furthermore, co-culture with amoeba resulted in some isolates demonstrating notable resistance against cell wall stressors and fluconazole, indicating increased stress tolerance compared to the unexposed isolates.…”

“…One notable response is the high expression of a PRX1 gene by C. parapsilosis during interactions with amoebae. This gene encodes a thioredoxin-linked peroxidase, which is vital for cell redox homeostasis and the response to oxidative stress ( Radosa et al., 2021 ). Moreover, other studies have revealed that C. auris can survive and proliferate within two amoebae species, Vermamoeba ( Hartmannella ) vermiformis and A. castellanii , suggesting that this environmental yeast has adapted to survive these fungal-predators ( Hubert et al., 2021 ).…”

“…Previous studies have reported the interaction between Candida parapsilosis and Protostelium aurantium . Notably, yeast cells exposed to reactive oxygen species (ROS) generated by predators have evolved strategies to respond to this stress ( Radosa et al., 2019 , 2021 ). Moreover, several virulence-related traits have been documented in Saccharomyces cerevisiae following interactions with amoebae, including an enhanced ability to grow at high temperatures, form pseudohyphae, undergo phenotypic switching, and exhibit resistance to oxidative stress ( Koller et al., 2016 ).…”

Toxin-Producing Endosymbionts Shield Pathogenic Fungus against Micropredators

“…Since fungi are able to utilize toxic secondary metabolites to protect themselves from predators and antagonistic organisms ( 10 – 12 ), we reason that rhizoxin might act as an antipredator agent in nonpathogenic Rhizopus strains. Effective defense strategies are particularly important for fungi since their high nutrient content, large biomass, and inability to move make fungi an ideal food source for micropredators such as soil-dwelling amoeba, nematodes, mites, and springtails ( 13 – 19 ). For example, the soil mold Aspergillus nidulans relies on secondary metabolites to defend itself against the fungivorous springtail Folsomia candida ( 20 , 21 ), while aflatoxin protects Aspergillus flavus from fungivory by insects ( 22 ).…”

Toxin-producing endosymbionts shield pathogenic fungus against micropredators

“…Since fungi are able to utilise toxic secondary metabolites to protect themselves from predators and antagonistic organisms (Boysen et al, 2021;Künzler, 2018;Spiteller, 2015), we reason that rhizoxin might act as an anti-predator agent in non-pathogenic Rhizopus strains. Effective defence strategies are particularly important for fungi as their high nutrient content, large biomass, and inability to move, makes fungi an ideal food source for micropredators such as soil-dwelling amoeba, nematodes, mites, and springtails (Baumann, 2018;Fierer, 2017;Fountain & Hopkin, 2005;Radosa et al, 2019;Radosa et al, 2021;Ruess & Lussenhop, 2005;Yeates et al, 1993). For example, the soil mould Aspergillus nidulans relies on secondary metabolites to defend itself against the fungivorous springtail Folsomia candida (Döll et al, 2013;Rohlfs et al, 2007), while aflatoxin protects Aspergillus flavus from fungivory by insects (Drott et al, 2017).…”