UTILIZATION OF PYRIMIDINE DERIVATIVES BY HYDROGENOMONAS FACILIS .2. DEGRADATION OF THYMINE AND URACIL BY WILD TYPE AND MUTANTS

35 mutant strains, unable to utilize uracil as a nitrogen source, were isolated from Hydrogenomonas facilis following treatment with 1-nitroso-3-nitro-1-methylguanidine and enrichment in a penicillin containing medium. One group of these mutants lacked dihydrouracil dehydrogenase and did not utilize thymine, orotic acid and uracil. A second group of mutants had lost the ability to form dehydrouracil hydrase and was unable to utilize uracil, orotic acid, thymine, dihydrouracil and dihydrothymine. The first group of these mutants excreted uracil, the second group dihydrouracil into the medium during growth with cytosine. The enzymes dihydrouracil dehydrogenase and dihydrouracil hydrase were present in much higher specific enzyme activities in cells grown with cytosine, uracil, thymine or orotic acid than in ammonia grown cells. Dihydroorotic dehydrogenase and dihydroorotase could not be demonstrated in cell-free extracts. These data indicate that both uracil and thymine are utilized as substrates by a non-specific hydrogenase and that both dihydrouracil and dihydrothymine are utilized by a non-specific hydrase. Both these enzymes are induced in presence of uracil, thymine or orotic acid in cells of Hydrogenomonas facilis. © 1969 Springer-Verlag.