Influences of Temperature and Adenine Concentration upon the Cultural Instability of a Red Adenine Auxotroph of Candida albicans

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Abstract
An adenine requiring strain of Candida albicans, blocked in purine biosynthesis at the conversion of 5-aminoimidazole ribotide (AIR) to 5-amino-4-imidazolecarboxylic acid ribotide, produces stable, red colonies when grown at 25[degree]C on growth-limiting amounts of adenine. Under comparable conditions at 37[degree]C, its colonies regularly exhibit overgrowing, white sectors. Genetic and physiological studies show that the parental strain is autointoxicated by AIR accumulated during growth on low levels of adenine at 37[degree]C but not 25[degree]C. The white sectors occur through selection of a homogeneous class of spontaneous mutants exhibiting reduced rates of purine biosynthesis and lesser tendency to accumulate AIR. The toxicity of AIR for C. albicans is restricted to strains of a particular genetic background and can be alleviated by exogenously provided basic amino acids or structurally related compounds.