Utilization of pyrimidines and pyrimidine deoxynucleosides by Thermobacterium acidophilum (Lactobacillus acidophilus).

Løvtrup, Søren (University of Göteborg, Sweden) and David Shugar. Utilization of pyrimidines and pyrimidine deoxynucleosides by Thermobacterium acidophilum (Lactobacillus acid-ophilus). J. Bacteriol. 82:623-631. 1961.-The utilization of pyrimidine deoxynucleosides was investigated by means of deoxyribosides of unnatural pyrimidines, especially by halogen-substituted uracil derivatives. All investigated deoxyribosides could be used, except that of N-methylthymidine. It was concluded that this substance cannot be a substrate for the enzyme trans-N-deoxyribosylase, which has been shown to be active in the utilization of deoxyribosides in this microorganism. With uracil as the only pyrimidine source, the halogen-substituted deoxyuridines had a certain inhibitory effect on growth. Contrary to previous findings, it was observed that normal growth occurs in the presence of thymine as the only pyrimidine source. The utilization of this substance is less efficient than that of uracil; a 1:10 dilution leads to a decrease in the extent of growth with the former, but not with the latter. From these results, complemented with experiments in which halogen-substituted uracil derivatives and the corresponding ribosides or deoxyribosides were used as inhibitors, it has been possible to account for most of the metabolic interconversions of pyrimidines in the investigated microorganism.