XVI International Botanical Congess

We studied adaptation in replicated experimental populations of the asexual, diploid, pathogenic yeast Candida albicans founded from a single cell and reared for 400 generations in the presence of inhibitory concentrations of the antifungal drug, fluconazole. Six populations were grown with fluconazole and six were grown without the drug. All six populations grown with fluconazole showed increased azole cross-resistance, but this increase followed strikingly different trajectories associated with various different mechanisms of azole resistance including overexpression of the ABC transporter genes, CDR1 and CDR2, a major facilitator gene, MDR1, and the gene encoding the target enzyme, ERG11. Also, several changes in neutral markers unrelated to drug resistance were detected in some, but not all, of the six populations exposed to drug, including loss of heterozygosity in marker genes heterozygous in the progenitor. We conclude that adaptation in these experimental populations is driven in part by chance events including mutation and mitotic recombination.