SUMMARY: A bacterial species which degrades the pyrimidines, uracil, thymine and cytosine by induced enzymes has been characterized as (strain S). All other strains of investigated oxidized thymine, but varied in their abilities to oxidize uracil and cystosine.

Organisms adapted to pyrimidines converted uracil to barbituric acid and thymine to 5-methylbarbituric acid. Oxidation of uracil by thymine-grown organisms was almost entirely by a pathway in which barbituric acid was an intermediate. Oxidation of thymine by uracil-grown organisms was similarly almost entirely via 5-methylbarbituric acid.

Oxidation of uracil by uracil-grown organisms and of thymine by thymine-grown organisms occurred, at least in part, through the respective barbituric acids. Discrepancies between the theoretical and observed values for O uptake suggested however that other pathways may also occur in these cases.

Pyrimidine-grown organisms oxidized 2-thiouracil to 2-thiobarbituric acid and 2-thiothymine to a compound which was probably 5-methyl-2-thiobarbituric acid. These products were not further degraded by the organism.

Barbituric acid was oxidized by uracil-grown organisms to CO, NH and urea with concurrent oxidative assimilation. The oxidation of barbituric acid was inhibited by isobarbituric acid and sodium azide although barbiturase activity in cell-free extracts was not affected by these substances. Barbiturase preparations converted barbituric acid anaerobically to malonic acid, CO and NH, but barbituric acid was not degraded by whole organisms under anaerobic conditions. Whole organisms, grown on uracil, degraded urea but did not oxidize malonic acid. Acetic and propionic but not malonic or barbituric acids were activated by cell-free extracts as judged by hydroxamate formation. From the evidence presented, it is unlikely that free malonic acid is an intermediate in the breakdown of barbituric acid.


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