Morphology Changes in Human Fungal Pathogens upon Interaction with the Host.

Zhongming Li,Kirsten Nielsen

doi:10.3390/jof3040066

Abstract

Morphological changes are a very common and effective strategy for pathogens to survive in the mammalian host. During interactions with their host, human pathogenic fungi undergo an array of morphological changes that are tightly associated with virulence. Candida albicans switches between yeast cells and hyphae during infection. Thermally dimorphic pathogens, such as Histoplasma capsulatum and Blastomyces species transform from hyphal growth to yeast cells in response to host stimuli. Coccidioides and Pneumocystis species produce spherules and cysts, respectively, which allow for the production of offspring in a protected environment. Finally, Cryptococcus species suppress hyphal growth and instead produce an array of yeast cells—from large polyploid titan cells to micro cells. While the morphology changes produced by human fungal pathogens are diverse, they all allow for the pathogens to evade, manipulate, and overcome host immune defenses to cause disease. In this review, we summarize the morphology changes in human fungal pathogens—focusing on morphological features, stimuli, and mechanisms of formation in the host.

Highlights

Fungi are both ubiquitous and highly diversified
Transition from yeast to mold in B. dermatitidis is controlled by two transcription factors SreB and HapX [49,50]
M. circinelloides, but the hererokaryon mutant pkaR4 shows a defect in germ tube emergence upon shift from anaerobic to aerobic growth, indicating that PkaR4 promotes the yeast to hyphal transition [63]

Summary

Introduction

Fungi are both ubiquitous and highly diversified. A “conservative” estimate for the number of fungal species is 1.5 million [1], with a recent estimate suggesting there may be over 5 million fungal species on earth [2]. These morphology changes dramatically influence the host-pathogen interaction and allow for these fungi to cause disease. The morphology switch between budding yeast and hyphal growth is triggered by diverse host environmental cues, including temperature, pH, serum, and CO2. A pescadillo homolog in C. albicans, is involved in the hyphae to yeast switch, especially in the budding of yeast from lateral filamentous cells [40] These detailed signal transduction pathway studies were recently expanded using genomic approaches. Detailed analysis of signal transduction pathways in C. albicans have identified an intricate network that coordinates signals from diverse environmental cues to modify basic cellular functions, such as cell cycle, membrane and cell wall synthesis, and transport These modifications allow for C. albicans to seamlessly transition between yeast and hyphal growth throughout its interaction with the host

Thermally Dimorphic Fungal Pathogens

Histoplasma Species

Blastomyces Species

Paracoccidioides Species

Summary

Fungal Pathogens That Exhibit Cell Size Variation

Pneumocystis Species

Coccidioides Species

Cryptococcus Species

Conclusions