microbiology, Vol 144, 1691-1697, Copyright © 1998 by Society for General Microbiology

ARTICLES

A novel quantitative mating assay for the fungal pathogen Cryptococcus neoformans provides insight into signalling pathways responding to nutrients and temperature

H Dong and W Courchesne
Department of Microbiology, School of Medicine, University of Nevada, Reno 89557-0046, USA.

Cryptococcus neoformans is a fungal pathogen that causes a lethal meningitis in immunocompromised individuals. Several factors are associated with virulence of this fungus, including its mating type; however, the mechanism by which mating type affects virulence is unknown. C. neoformans is a basidiomycete that exists in two mating types called a and alpha that can fuse to form an a/alpha dikaryon. A mating assay was developed that allowed a quantitative analysis of cryptococcal mating physiology. Interestingly, the efficiency of mating appeared to be dependent on temperature, being highest at 30 degrees C and almost completely absent at 37 degrees C. Thus, while mating type itself may be associated with virulence (which must occur at 37 degrees C), the ability to mate is probably not a virulence factor. Mating efficiency was increased by altering the carbon or nitrogen sources to give so-called starvation media. The addition of various drugs also seemed to alter the frequency of mating, depending on the composition of mating medium. The data suggested that cAMP, 8-bromo-cAMP and caffeine increased mating on starvation medium but only cAMP and 8- bromo-cAMP stimulated mating on rich medium; caffeine was unable to stimulate mating on rich medium. Aluminium fluoride, an activator of heterotrimeric GTP-binding proteins (G-proteins), was also found to stimulate mating, suggesting the involvement of a G-protein that may regulate the level of cAMP.

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