GENETIC AND BIOCHEMICAL STUDIES ON 5′-NUCLEOTIDE FERMENTATION

1.The presence or absence of GMP reductase had no effect on nucleoside production in adenine-requiring mutants of Bacillus subtilis K, which produced a large amount of inosine when cultured in an adenine-limited medium.2. Mutants resistant to 8-azaxanthine were derived from strain 38-3, a GMP reductase-positive inosine producer, and from strain 30-12, a GMP reductase-negative inosine producer. About 60% of the resistant mutants from strain 38-3 were found to produce xanthosine as well as inosine, while 70% of the resistant mutants from strain 30-12 produced guanosine as well as inosine. Loss of the adenine requirement in these 8-azaxanthine-resistant mutants reduced the accumulation of xanthosine or guanosine and completely halted the accumulation of inosine. Many more mutants with an altered nucleoside accumulation pattern were obtained when 8-azaxanthine was used as a selective agent than when 8-azaguanine was used.3.Guanine-requiring mutants, GU-16 and 308-18, were isolated respectively from an 8-azaxanthine-sensitive inosine producer and from an 8-azaxanthine-resistant xanthosine-inosine producer, and the effects of guanosine on xanthosine and inosine formation were compared in these two guanine auxotrophs; strain GU-16 produced a large amount of xanthosine only when grown in media containing limited amounts of guanosine, and the production was sharply reduced by higher amounts of guanosine. In strain 308-18, however, xanthosine formation was not so greatly affected by exogenous guanosine as in strain GU-16. There was no difference in the effect of guanosine on the total amount of purine nucleosides produced, including both xanthosine and inosine, in these two strains.