Biosynthesis of Thymine and Formyltetrahydrofolate

SUMMARY In Lactobacillus leichmannii, ATCC 7830, the conversion of folic acid to tetrahydro derivatives occurs in the presence or absence of vitamin Blz. No qualitative difference in the forms of these derivatives was detected by bioautography. A slight increase in the formation of these derivatives was found when cells from cultures grown on deoxyribonucleosides in the absence of vitamin B12 were incubated with folic acid. No difference in the specific activity of the thymine after the incorporation of formate into deoxyribonucleic acid was noted when cultures were grown in the absence of vitamin Big. Evidence of unbalanced growth was found when cultures were grown for 24 hours in media supplemented with 2’-deoxyribonucleosides in place of vitamin Blz; deoxyribonucleic acid per gram of washed and dried cells was reduced to one-fifth the amount found in cells grown on vitamin B,,.