Extensive Metabolic Remodeling Differentiates Non-pathogenic and Pathogenic Growth Forms of the Dimorphic Pathogen Talaromyces marneffei

Abstract

Fungal infections are an increasing public health problem, particularly in immunocompromised individuals. While these pathogenic fungi show polyphyletic origins with closely related non-pathogenic species, many undergo morphological transitions to produce pathogenic cell types that are associated with increased virulence. However, the characteristics of these pathogenic cells that contribute to virulence are poorly defined. Talaromyces marneffei grows as a non-pathogenic hyphal form at 25°C but undergoes a dimorphic transition to a pathogenic yeast form at 37°C in vitro and following inhalation of asexual conidia by a host. Here we show that this transition is associated with major changes in central carbon metabolism, and that these changes are correlated with increased virulence of the yeast form. Comprehensive metabolite profiling and 13C-labeling studies showed that hyphal cells exhibited very active glycolytic metabolism and contain low levels of internal carbohydrate reserves. In contrast, yeast cells fully catabolized glucose in the mitochondrial TCA cycle, and store excess glucose in large intracellular pools of trehalose and mannitol. Inhibition of the yeast TCA cycle inhibited replication in culture and in host cells. Yeast, but not hyphae, were also able to use myo-inositol and amino acids as secondary carbon sources, which may support their survival in host macrophages. These analyses suggest that T. marneffei yeast cells exhibit a more efficient oxidative metabolism and are capable of utilizing a diverse range of carbon sources, which contributes to their virulence in animal tissues, highlighting the importance of dimorphic switching in pathogenic yeast.

Metabolic Peculiarities of Paracoccidioides brasiliensis Dimorphism as Demonstrated by iTRAQ Labeling Proteomics

“…In addition, proteins related to the TCA were more abundant in yeast cells compared to transition phase and mycelium and enzymes of glycolysis were down regulated. These data strongly support the observed metabolic preference for the TCA cycle and respiration and are in agreement with similar observations in Talaromyces marneffei (Pasricha et al, 2017). This is also in accordance with biochemical data published for Paracoccidioides sp.…”

A mutation in C. neoformans mitochondrial NADH dehydrogenase results in increased virulence in mice

“…Thus, these data may explain the observed decrease in survival, as in various bacteria, changes in metabolism after colonization of a new niche have been linked to increases in virulence [ 42 ]. Additionally, the pathogenic yeast form of the fungus Talaromyces marneffei has 3–7-fold higher levels of TCA cycle intermediates compared to the nonpathogenic hyphal form, which affects yeast growth in THP-1 macrophages, suggesting that increased metabolism affects growth and virulence [ 43 ]. This has also been observed in C. albicans , where a mutant with increased respiration forms biofilms better than the wildtype strain [ 44 ].…”

Talaromyces marneffei simA Encodes a Fungal Cytochrome P450 Essential for Survival in Macrophages

“…Wild-type, Δ simA , and Δ simA simA + strains were cultured in brain heart infusion (BHI) medium for 4 days at 37°C. A 10-ml volume of this yeast culture was transferred to a fresh BHI flask, and mid-log-phase yeast cells were harvested after 20 h ( 59 ). Separate polar and sterol metabolomic analyses were performed on 4 biological repeats for each strain, with 4 technical repeats.…”

“…Separate polar and sterol metabolomic analyses were performed on 4 biological repeats for each strain, with 4 technical repeats. Yeast cells (1 × 10 8 ) were metabolically quenched by rapid filtration on sterilized filter disks using a suction apparatus and were then dried ( 59 ). The filter disks were divided into four replicates (2.5 × 10 7 ) and then lysed in 3:1 (vol/vol) methanol/Milli-Q water (600 µl) using a freeze/thaw method, where samples were cycled (10 times for 30 s each time) in liquid N2, followed by a dry ice/ethanol bath.…”