Induction of colony morphology variation in Rhodotorula gracilis by UV irradiation

Nonlethal UV irradiation induced an unusually high frequency of colony morphology variation in Rhodotorula gracilis. The variation was not fixed but indicated further variability in subsequent platings. Microscopic examination of the cultures indicated that UV-irradiated variants had grossly varying types of shapes and arrangements of cells in contrast to the uniformly shaped and budding cells of the nonirradiated culture. Flow-cytometric analysis of a colony variant suggested a slightly higher proportion of cells with variable DNA content than the nonirradiated culture. Extensive biochemical characterization revealed only one difference in that the nonirradiated culture had a partial requirement for pantothenate while the colony variant was completely independent of this requirement. We speculate that UV triggers a yet unstudied means of variability in R. gracilis with possible accompanying recombinational events.