Further studies on mutant strains of Ophiostoma which require guanine.

Biochemical mutants which require guanine but are unable to utilize adenine and hypoxanthine obviously represent a very rare type of purine deficiency in microorganisms. So far, guanineless mutations have been observed only in the ascomycet,ous fungus, Ophiostoma multiannulatum, in which seven strains of this biochemical type were isolated after x-ray or ultraviolet irradiation (l-3). Three of these strains were obtained with the aid of a selective enrichment technique (3). In previous studies the nutritional requiremenbs of some of these guanineless mutants were analyzed from a quantitative point of view, and it was also found that adenine and hypoxanthine inhibited their rate of growth (2). In the present communication, certain new facts are reported regarding the physiology of the guanineless Ophiostoma mutants, e.g. the effect of 2,6-diaminopurine. Their peculiar tendency to change spontaneously into guanine-hypoxanthineless double mutants has also been investigated and is explained as a consequence of certain biochemical peculiarities of the mutants in question.