Bidirectional stimulation of the white-opaque transition of Candida albicans by ultraviolet irradiation.

Most strains of Candida albicans are capable of switching spontaneously and at high frequency between a number of phenotypes distinguishable by colony morphology. The switching frequency of Candida albicans strain WO-1 between two predominant phenotypes, 'white' and 'opaque', and a minor phenotype, 'fuzzy', increased dramatically with low doses of ultraviolet irradiation that killed less than 20% of the population. The ultraviolet irradiation effect continued to be expressed over many generations as evidenced by stimulated sectoring. Ultraviolet irradiation stimulated switching in both the white-to-opaque and opaque-to-white direction, suggesting that a common mechanism functions in both directions.