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Cryptococcus neoformans Mates on Pigeon Guano: Implications for the Realized Ecological Niche and Globalization

Departments of Molecular Genetics and Microbiology,¹ Medicine,² Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710³

Received 27 March 2007/ Accepted 6 April 2007

The ecological niche that a species can occupy is determined by its resource requirements and the physical conditions necessary for survival. The niche to which an organism is most highly adapted is the realized niche, whereas the complete range of habitats that an organism can occupy represents the fundamental niche. The growth and development of Cryptococcus neoformans and Cryptococcus gattii on pigeon guano were examined to determine whether these two species occupy the same or different ecological niches. C. neoformans is a cosmopolitan pathogenic yeast that infects predominantly immunocompromised individuals, exists in two varieties (grubii [serotype A] and neoformans [serotype D]), and is commonly isolated from pigeon guano worldwide. By contrast, C. gattii often infects immunocompetent individuals and is associated with geographically restricted environments, most notably, eucalyptus trees. Pigeon guano supported the growth of both species, and a brown pigment related to melanin, a key virulence factor, was produced. C. neoformans exhibited prolific mating on pigeon guano, whereas C. gattii did not. The observations that C. neoformans completes the life cycle on pigeon guano but that C. gattii does not indicates that pigeon guano could represent the realized ecological niche for C. neoformans. Because C. gattii grows on pigeon guano but cannot sexually reproduce, pigeon guano represents a fundamental but not a realized niche for C. gattii. Based on these studies, we hypothesize that an ancestral Cryptococcus strain gained the ability to sexually reproduce in pigeon guano and then swept the globe.

Published ahead of print on 20 April 2007.

This article has been cited by other articles:

• Sun, S., Xu, J. (2007). Genetic Analyses of a Hybrid Cross Between Serotypes A and D Strains of the Human Pathogenic Fungus Cryptococcus neoformans. Genetics 177: 1475-1486 [Abstract] [Full Text]