The Effect of Ribonucleotides on the Deoxyribonucleic Acid Metabolism of Lactobacillus acidophilus R-26*

La&bacillus (Thermobacterium) acidophilus R-26 has a specific requirement for a preformed deoxyribonucleoside residue. Oligodeoxyribonucleotides and 5’-deoxyribonucleotides are active. However, this requirement is not replaced by vitamin Blz (1, 2). Previous nutritional studies have shown that ribonucleotides inhibit the deoxyribonucleoside activity’ of 5’-deoxyribonucleotides for L. acidophilis (3). This inhibition was reversed by increasing levels of 5’-deoxyribonucleotides or deoxyribonucleosides and deoxyribonucleosides were more active in reversing the inhibition caused by ribonucleotides than were 5’-deoxyribonucleotides. Phosphate, ribose 5’-phosphate, ribonucleosides, and purine or pyrimidine bases substituted in amounts equivalent to or in excess of the ribonucleotides did not influence the deoxyribonucleoside activity of 5’-deoxyribonucleotides for L. acidophilus. Purine ribonucleotides were generally more active inhibitors of the deoxyribonucleoside activity of 5’-deoxyribonucleotides indicating their effect may not be to compete with 5’deoxyribonucleotide for permeability into the cell. In all the results reported in the previous studies and in the following experiments, the morphology of L. acidophilus was of the elongated or filamentous form. The formation of elongated or filamentous cells by L. acidophilus under conditions in which the level of required deoxyribonucleoside is limited, has been previously reported by Jeener and Jeener (4). Investigations were undertaken to study the biochemical mechanisms by which the deoxyribonucleoside activity of 5’-deoxyribonucleotides for L. acidophilus is inhibited in the presence of ribonucleotides. The DNA and RNA metabolism of L. acidophilus was studied under a variety of nutritional conditions with particular reference to the precursor pools of RNA and DNA metabolism and the RNA and DNA composition of the cells.