Carbon dioxide is a powerful inducer of monokaryotic hyphae and spore development in Cryptococcus gattii and carbonic anhydrase activity is dispensable in this dimorphic transition.

Ping Ren,Sudha Chaturvedi,Vishnu Chaturvedi,Yong-Sun Bahn

doi:10.1371/journal.pone.0113147

Abstract

Cryptococcus gattii is unique among human pathogenic fungi with specialized ecological niche on trees. Since leaves concentrate CO2, we investigated the role of this gaseous molecule in C. gattii biology and virulence. We focused on the genetic analyses of β-carbonic anhydrase (β-CA) encoded by C. gattii CAN1 and CAN2 as later is critical for CO2 sensing in a closely related pathogen C. neoformans. High CO2 conditions induced robust development of monokaryotic hyphae and spores in C. gattii. Conversely, high CO2 completely repressed hyphae development in sexual mating. Both CAN1 and CAN2 were dispensable for CO2 induced morphogenetic transitions. However, C. gattii CAN2 was essential for growth in ambient air similar to its reported role in C. neoformans. Both can1 and can2 mutants retained full pathogenic potential in vitro and in vivo. These results provide insight into C. gattii adaptation for arboreal growth and production of infectious propagules by β-CA independent mechanism(s).

Highlights

Cryptococcus gattii, a basidiomycetous yeast, is an emerging pathogen in North America causing fatal disease in both healthy and immunocompromised humans as well in a wide range of animals including birds, domestic and wild mammals [1, 2]
CAN2 but not CAN1 is a major b-carbonic anhydrase (b-carbonic anhydrase (CA)) required for C. gattii growth at ambient air
These results indicated that CAN2 but not CAN1 is essential for C. gattii growth in ambient air

Summary

Introduction

Cryptococcus gattii, a basidiomycetous yeast, is an emerging pathogen in North America causing fatal disease in both healthy and immunocompromised humans as well in a wide range of animals including birds, domestic and wild mammals [1, 2]. Xue et al [11] have demonstrated that the young Arabidopsis thaliana plant surfaces represent a permissible environment, in which C. gattii and its closely related species C. neoformans can complete their sexual cycle (a-a mating). This intriguing finding raised the possibility that plants might serve as a critical host in the production of infectious propagules in the form of sexual spores (basidiospores). A number of studies raised the possibility that monokaryotic fruiting (a-a mating or same sex mating) might be a widespread phenomenon in C. neoformans var. A recent study from C. neoformans var. neoformans found cell cycle arrest induced mating-independent monokaryotic fruiting[17]

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