For the immune compromised, Cryptococcus neoformans is something to worry about: it causes over 1 million cases of meningitis annually and is the leading cause of fungal meningitis in immunosuppressed individuals, including AIDS patients. Despite all this, we still know few details about C. neoformans’ sexual cycle and why this pathogen infects the central nervous system.
A new study reveals some intriguing clues, however: it turns out C. neoformans has a sweet tooth for inositol – a sugar that’s abundant in the central nervous system. This could explain why this species does so well in inositol-rich brain and nervous tissue.
Frederick Ausubel of the Genetics Department at Harvard’s Medical School and a member of mBio’s Board of Editors, says the paper, which is coming out in the inaugural issue of mBio, reveals C. neoformans has a much larger inositol transporter gene family than expected. Most fungi have inositol transporters, Ausubel explains, “but C. neoformans appears to be unusual because it has a relatively large family of inositol transporters whereas other fungi have fewer.” Xue et al. detected over ten members of the myo-inositol transporter (ITR) gene family among various strains of C. neoformans. Most other fungi have only two.
So what does having lots of inositol transporters mean? For C. neoformans, it means that acquiring inositol is important for infectivity and for stimulating mating. Xue et al. demonstrated that without inositol or the full complement of genes to acquire or synthesize it, mating in C. neoformans is hindered and it isn’t nearly as effective as a pathogen.
Ausubel says the work suggests that C. neoformans likes life in inositol-rich places. He points out that, besides living in brains, the organism is found in the wild on eucalyptus leaves, which are also loaded with inositol. “It may specifically seek out environments rich in inositol,” says Ausubel.
The authors of the study speculate that the large ITR gene family in Cryptococcus may well result from co-evolution between the pathogen and its environmental niches and host conditions.