Degradation of the pyrimidine bases uracil and thymine by Escherichia coli B

Degradation of the pyrimidine bases uracil and thymine by Escherichia coli B was investigated. The known products of the reductive pathway of pyrimidine base catabolism were tested to determine if they could support the growth of E. coli B cells as sole sources of nitrogen or carbon. As might be expected if the reductive pathway was present, it was found that dihydrouracil, N-carbamoyl-beta-alanine, beta-alanine, dihydrothymine and beta-aminoisobutyric acid could sustain the growth of the bacterial cells as sole nitrogen sources by at least a fourteen-fold greater level than that observed if they were included as sole carbon sources. The existence of the reductive pathway of pyrimidine base degradation was confirmed in this micro-organism, since dihydrouracil, N-carbamoyl-beta-alanine and beta-alanine were detected following thin-layer chromatographic separation of the catabolic products of uracil and dihydrouracil.