Originally published as Genetics Published Articles Ahead of Print on February 3, 2005.

Genetics, Vol. 169, 1883-1890, April 2005, Copyright © 2005
doi:10.1534/genetics.104.038737

Increased Virulence and Competitive Advantage of a/{alpha} Over a/a or {alpha}/{alpha} Offspring Conserves the Mating System of Candida albicans

Shawn R. Lockhart, Wei Wu, Joshua B. Radke, Rui Zhao and David R. Soll1

Department of Biological Sciences, The University of Iowa, Iowa City, Iowa 52242-1324

1 Corresponding author: Department of Biological Sciences, Room 302 BBE, University of Iowa, Iowa City, IA 52242.
E-mail: david-soll{at}uiowa.edu

The majority of Candida albicans strains in nature are a/{alpha} and must undergo homozygosis to a/a or {alpha}/{alpha} to mate. Here we have used a mouse model for systemic infection to test the hypothesis that a/{alpha} strains predominate in nature because they have a competitive advantage over a/a and {alpha}/{alpha} offspring in colonizing hosts. Single-strain injection experiments revealed that a/{alpha} strains were far more virulent than either their a/a or {alpha}/{alpha} offspring. When equal numbers of parent a/{alpha} and offspring a/a or {alpha}/{alpha} cells were co-injected, a/{alpha} always exhibited a competitive advantage at the time of extreme host morbidity or death. When equal numbers of an engineered a/a/{alpha}2 strain and its isogenic a/a parent strain were co-injected, the a/a/{alpha}2 strain exhibited a competitive advantage at the time of host morbidity or death, suggesting that the genotype of the mating-type (MTL) locus, not associated genes on chromosome 5, provides a competitive advantage. We therefore propose that heterozygosity at the MTL locus not only represses white-opaque switching and genes involved in the mating process, but also affects virulence, providing a competitive advantage to the a/{alpha} genotype that conserves the mating system of C. albicans in nature.




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