Importance of Mitochondria in Survival of Cryptococcus neoformans Under Low Oxygen Conditions and Tolerance to Cobalt Chloride

Abstract

Cryptococcus neoformans is an environmental fungal pathogen that requires atmospheric levels of oxygen for optimal growth. For the fungus to be able to establish an infection, it must adapt to the low oxygen concentrations in the host environment compared to its natural habitat. In order to investigate the oxygen sensing mechanism in C. neoformans, we screened T-DNA insertional mutants for hypoxia-mimetic cobalt chloride (CoCl2)-sensitive mutants. All the CoCl2-sensitive mutants had a growth defect under low oxygen conditions at 37°C. The majority of mutants are compromised in their mitochondrial function, which is reflected by their reduced rate of respiration. Some of the mutants are also defective in mitochondrial membrane permeability, suggesting the importance of an intact respiratory system for survival under both high concentrations of CoCl2 as well as low oxygen conditions. In addition, the mutants tend to accumulate intracellular reactive oxygen species (ROS), and all mutants show sensitivity to various ROS generating chemicals. Gene expression analysis revealed the involvement of several pathways in response to cobalt chloride. Our findings indicate cobalt chloride sensitivity and/or sensitivity to low oxygen conditions are linked to mitochondrial function, sterol and iron homeostasis, ubiquitination, and the ability of cells to respond to ROS. These findings imply that multiple pathways are involved in oxygen sensing in C. neoformans.

Identification of Hypoxia-Inducible Target Genes of Aspergillus fumigatus by Transcriptome Analysis Reveals Cellular Respiration as an Important Contributor to Hypoxic Survival

“…Our data and previous studies on A. fumigatus and other fungi indicated an association of functional mitochondria with the ability to adapt to low-oxygen environments (11,17,(67)(68)(69)(70). The upregulation of several respiratory genes during long-term exposure to hypoxia is also consistent with the increased production of components of the electron transport chain and oxidative phosphorylation on the proteome level (12,13).…”

The fatal fungal outbreak on Vancouver Island is characterized by enhanced intracellular parasitism driven by mitochondrial regulation

“…Hence the tubular morphology is likely to be a result of up-regulation of many candidate genes listed in Table S3. Early studies on Cryptococcus have demonstrated the importance of mitochondria in responding to hypoxic conditions and oxidative stress (30,31). We therefore propose that, after being engulfed by macrophages, the VIO strains are able to promote mitochondrial fusion to form long tubular mitochondria to more efficiently repair mtDNA damage caused by the oxidative species and hypoxic conditions present within the macrophage phagosome.…”

Unusual Galactofuranose Modification of a Capsule Polysaccharide in the Pathogenic Yeast Cryptococcus neoformans

“…Finally, it is possible that Galf plays a role under conditions not included in our analysis. C. neoformans is an extremely adaptable environmental yeast that can withstand a variety of harsh conditions (63)(64)(65) and is capable of living in close association with numerous organisms, including plants (66,67), birds (68,69), predatory amoebae (70), and mammals (71,72), notably humans (73,74). The cryptococcal capsule in particular is a dynamic structure whose morphology and architecture change with growth conditions (75)(76)(77) and the local environment (52,55).…”