Same-sex fungi can mate

Cryptococcus neoformans causes life-threatening meningoencephalitis in immunocompromised patients. The fungus has two sexes, alpha and a, but the vast majority ofC. neoformans isolates seen clinically and in the environment are alpha, leaving them with apparently few chances to mate. "Normally when you have sexually reproducing organisms, you find both sexes in roughly equal numbers," Heitman told The Scientist.During mating, C. neoformans develops filaments and spores. Haploid alpha strains can also grow filaments and spores in a process known as fruiting, which researchers thought was asexual and mitotic. To see if diploidization occurred during fruiting, Heitman and colleagues cultured cells from the buds of fruiting haploid alpha strain filaments. Fluorescence-activated cell sorting (FACS) analysis revealed 97% of them were diploid.To look at whether fruiting involves chromosome assortment and recombination, the researchers examined spores from a diploid alpha-alpha strain constructed from a pair of strains marked with transgenes for either nourseothricin or neomycin resistance. Nourseothricin and neomycin transgenes showed independent assortment, and FACS analysis revealed that the diploid strain's spores were all haploid. Study of markers throughout spore genomes revealed that recombination occurred at a rate similar to alpha-a sexual reproduction. All progeny possessed unique genotypes, none identical to either parent, consistent with meiotic recombination.Same-sex mating could help C. neoformans generate the genetic diversity associated with sexual reproduction when the opposite sex is rare, Heitman suggested. "This may explain the emergence of this organism as a successful human pathogen, and one that is distributed worldwide rather than being geographically restricted - as is the case, luckily, with many other human fungal pathogens," he told The Scientist."Many organisms are thought to reproduce only asexually because no mating partner has been found," no