Cryptococcus neoformans adapts to host CO ₂ concentrations through the coordinated remodeling of central carbon metabolism, oxidative stress resistance, and membrane homeostasis

Cryptococcus neoformans is an environmental pathogen that remodels its cellular physiology to survive within mammals and, in susceptible hosts, cause life-threatening meningoencephalitis. Of the many distinctions between the external environment and mammalian tissues, CO ₂ concentration in the host is 2 orders of magnitude higher than in the environment and represent a critical stress for C. neoformans . C. neoformans strains that do not replicate at host CO ₂ concentrations are less virulent in mouse models of infection, further supporting CO ₂ tolerance as a virulence trait. To further understand the genetic determinants of C. neoformans CO ₂ tolerance, we performed a near genome-wide screen for deletion mutants with altered CO ₂ fitness using a competitive growth assay. A total of 301 of 4698 deletion mutants showed altered CO ₂ tolerance (245 reduced fitness; 51 increased fitness) demonstrating the global effect of host CO ₂ on C. neoformans physiology. Based on this data set as well as a metabolomic analysis of C. neoformans adaptation to host CO ₂ , we show that remodeling of central carbon metabolism, oxidative stress buffering and membrane homeostasis represent an integrated response to CO ₂ stress that is mediated in part by the TOR-Ypk1 signaling axis. We propose that CO ₂ -induced capsule formation leads to reduced cellular glucose which, in turn, triggers remodeling of central carbon metabolism toward utilization of alternative carbon sources and increased mitochondrial respiration/reactive oxygen generation. Thus, these data provide a near genome-wide profile of the genetic determinants of C. neoformans CO ₂ tolerance as well as a model for how this important environmental human fungal pathogen alters its physiology to proliferate in the host.