Genetics. Published Articles Ahead of Print: February 3, 2005, Copyright © 2005
doi:10.1534/genetics.104.038737


A more recent version of this article appeared on April 1, 2005.

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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 1, Wei Wu 1, Joshua B. Radke 1, Rui Zhao 1 and David R. Soll 1*

1 The University of Iowa

* To whom correspondence should be addressed. E-mail: david-soll{at}uiowa.edu.

Submitted on November 19, 2004
Revised on December 9, 2004
Accepted on 24 December 2004


Abstract

The majority of Candida albicans strains in nature are a/{alpha} and must undergo homozygosis to a/a or {alpha}/{alpha} in order 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, provide 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.

Key Words: Candida virulence, Model for systemic candidiasis, mating type locus zygosity




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