Abstract
The transcription factor EFG1 functions as a suppressor of white-to-opaque and white-to-gray switching in a/α strains of Candida albicans In a collection of 27 clinical isolates, 4 of the 17 EFG1/EFG1 strains, 1 of the 2 EFG1/efg1 strains, and all 8 of the efg1/efg1 strains underwent white-to-opaque switching. The four EFG1/EFG1 strains, the one EFG1/efg1 strain, and one of the eight efg1/efg1 strains that underwent switching to opaque did not switch to gray and could not be complemented with a copy of EFG1 Competition experiments in a mouse model for gastrointestinal (GI) colonization confirmed that efg1/efg1 cells rapidly outcompete EFG1/EFG1 cells, and in plating experiments, formed colonies containing both gray and opaque cells. Direct microscopic analysis of live cells in the feces, however, revealed that the great majority of cells were opaque, suggesting opaque, not gray, may be the dominant phenotype at the site of colonization.IMPORTANCE Close to half of a collection of 27 clinical a/α isolates of Candida albicans underwent white-to-opaque switching. Complementation experiments revealed that while approximately half of the a/α switchers were due to EFG1 mutations, the remaining half were due to mutations in other genes. In addition, the results of competition experiments in a mouse GI tract colonization model support previous observations that efg1/efg1 cells rapidly outcompete EFG1/EFG1 strains, but direct microscopic analysis reveals that the major colonizing cells were opaque, not gray.
Highlights
The transcription factor EFG1 functions as a suppressor of white-toopaque and white-to-gray switching in a/␣ strains of Candida albicans
Direct microscopic observations of live colonizing cells in the feces revealed that a/␣ strains with EFG1 null mutations expressed almost exclusively the opaque, not gray, phenotype, suggesting plating experiments may not accurately assess the cell phenotypes expressed at the site of GI colonization
These results indicate that the majority of efg1⌬/efg1⌬ cells colonizing the feces after 8 days postingestion express the opaque, not gray, phenotype, and that the results of the plating experiments performed here (Fig. 5E) and previously (23) may not accurately reflect the actual cellular phenotype of efg1/efg[1] cells at the site of GI colonization
Summary
The transcription factor EFG1 functions as a suppressor of white-toopaque and white-to-gray switching in a/␣ strains of Candida albicans. The results of competition experiments in a mouse GI tract colonization model support previous observations that efg1/efg[1] cells rapidly outcompete EFG1/EFG1 strains, but direct microscopic analysis reveals that the major colonizing cells were opaque, not gray. Direct microscopic observations of live colonizing cells in the feces revealed that a/␣ strains with EFG1 null mutations expressed almost exclusively the opaque, not gray, phenotype, suggesting plating experiments may not accurately assess the cell phenotypes expressed at the site of GI colonization. The latter results suggest that a/␣ efg1/efg[1] strains colonizing the GI tract may express the opaque, not gray, phenotype
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