Growth of Lactobacillus bulgaricus in milk. 2. Characteristics of purine nucleotides, pyrimidine nucleotides, and nucleic acid synthesis

Lactobacillus bulgaricus incorporated exogenous guanine only into guanine nucleotides and not into adenine nucleotides. Lactobacillus bulgaricus lacks the ability to interconvert adenine nucleotides and guanine nucleotides. Biosynthesis of pyrimidine nucleotides from orotic acid was depressed by addition of guanosine monophosphate or adenosine monophosphate. Some step in pyrimidine biosynthesis from orotic acid may be negatively regulated by the intracellular amount of purine nucleotides. Lactobacillus bulgaricus could not grow in milk from which orotate was removed. This indicates that the activity of de novo pyrimidine synthesis is very low in this organism. When the intracellular amount of purine or pyrimidine base was limited, ribonucleic acid synthesis was markedly depressed, resulting in cell elongation, whereas deoxyribonucleic acid synthesis was not so much affected.