Thymineless death inLactobacillus acidophilus R-26

Abstract

Thymineless death (TLD) was studied inLactobacillus acidophilus R-26. Thymine synthesis was inhibited with 5-fluorouracil (FU) or deoxyadenylate (dAMP) or by the absence of folic acid. In the case of FU, the maximum rate of dying was obtained at concentrations exceeding 0.1 μg/ml. This concentration did not affect the growth of the bacteria in the presence of thymine (4 μg/ml) and uracil (10 μg/ml). At higher FU concentrations up to 10 μg/ml, the course of TLD was unaltered, but the growth of bacteria in complete medium was slower. In the case of dAMP, the same course of TLD was obtained at a concentration of 150 μg/ml. If 1,500 μg dAMP/ml was used, the pre-death lag phase was shortened the rate of dying being unaltered. These concentrations of dAMP retarded the growth of bacteria even in a complete medium. If the thymine synthesis was prevented by the absence of folic acid the rate of dying was much lower than that caused by the presence of FU or dAMP. This was true even if the aminopterin was added. The authors conclude that the folic acid starvation did not inhibit completely the synthesis of thymine.