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

Shivani Pasricha,Malcolm J Mcconville,Hwa H Chua,Jenny Chambers,Alex Andrianopoulos,Kylie J Boyce,James I Macrae

doi:10.3389/fcimb.2017.00368

Shivani Pasricha, Malcolm J Mcconville + Show 5 more

Open Access

https://doi.org/10.3389/fcimb.2017.00368

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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.

Highlights

Pathogenic microbes frequently have to adjust their cellular metabolism in order to exploit particular nutrient conditions in the infected host tissues and/or to effectively respond to physical or microbiocidal stresses imposed on them by the host (Rohmer et al, 2011)
Both hyphal and yeast cells undergo exponential growth when suspended in fresh medium before reaching stationary growth, the maximum rates of biomass accumulation differ between the two cell types (Figure S1)
To determine whether both cell types exhibit similar carbon source utilization during exponential growth, T. marneffei hyphal and yeast cells were cultivated in complex heart infusion (HI) medium and changes in potential carbon sources in the medium over 24 h monitored by GC-MS (Figure 1A, Tables S1, S2)

Summary

Introduction

Pathogenic microbes frequently have to adjust their cellular metabolism in order to exploit particular nutrient conditions in the infected host tissues and/or to effectively respond to physical or microbiocidal stresses imposed on them by the host (Rohmer et al, 2011). For many microbes, including an increasing number of dimorphic fungal pathogens such as the opportunistic. In common with a number of other pathogenic fungi, T. marneffei undergoes a reversible morphological switch from a filamentous, multicellular (hyphal or pseudohyphal) to a unicellular (yeast) growth form. Macrophages, phagocytose inhaled conidia and it is within these host cells that they undergo the dimorphic switch to the pathogenic yeast form. The dimorphic switch from the hyphal to yeast form is considered a key virulence attribute that allows this fungus to survive within this hostile host niche

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