The utilization of dihydrothymine by Streptococcus faecalis in the absence of folic acid and thymine.

Stokes (1944) reported the replaceability of folic acid by thymine for Streptococcus lactis strain R as well as other folic-acid-requiring streptococci, and Fink et al. (1954) noted that high concentrations of recrystallized dihydrothymine supported growth of Streptococcus faecalis (ATCC 8043) deficient in both folic acid and thymine. The question arose, however, as to whether the latter response might be due to trace amounts of thymine present in the dihydrothymine, and it was difficult to rule out this possibility by ordinary analytical methods. The present paper describes the results of a microbiological test for residual thymine-like activity following subjection of preparations of dihydrothymine to mildly alkaline conditions under which thymine was stable but dihydrothymine was hydrolyzed to jl-ureidoisobutyric acid (Fink et al., 1954; Batt et al., 1954).