The assimilation of amino-acids by bacteria. XV. Actions of antibiotics on nucleic acid and protein synthesis in Staphylococcus aureus.

In previous papers of this series, experimental conditions have been described which will enable the following processes to be studied in washed suspensions of Staphylococcus aureus (Micrococcus pyogenes var. aureus): internal accumulation of free glutamic acid (Gale, 1947 a, b), extracellular accumulation of peptides containing glutamic acid (Gale & Van Halteren, 1951), accumulation of combined glutamic acid within the cells (Gale, 1951 b) and synthesis of protein and nucleic acid (Gale & Folkes, 1953). Aureomycin and chloramphenicol inhibit the increase of cellular combined glutamate at lower concentrations than those necessary to prevent the accumulation of free glutamic acid within the cells, whereas sodium azide, 2:4-dinitrophenol and 8-hydroxyquinoline affect these processes to approximately the same extent (Gale & Paine, 1951). Penicillin and bacitracin have no effect upon the accumulation of free or combined glutamic acid in washed suspensions of cells, but if either of these antibiotics is added to the growth medium an hour before harvesting, the resulting cells are unable to accumulate either free or combined glutamic acid (Gale & Taylor, 1947; Gale & Paine, 1951; Paine, 1951). Hotchkiss (1950) has described a disorganization of protein synthesis by penicillin which results, under the conditions of his experiments, in extracellular accumulation of peptides when Staph. aureus is incubated with amino-acid mixtures. Mitchell & Moyle (1951) followed the nucleic acid content of Staph. aureus during normal growth and in the presence of penicillin. During the normal phase of accelerated growth they found that nucleic acid reproduced more rapidly than cell dry weight, suggesting that nucleic acid controlled the rate of cell synthesis. A disturbance of nucleic acid metabolism occurred in the presence ofpenicillin and was accompanied by an intracellular accumulation of extractable nucleotides. Krampitz & Werkman (1947) and Gros & Macheboeuf (1948a, b) have previously described inhibitions of nucleic acid metabolism in bacterial cells by high concentrations of penicillin, while Gros, Beljanski & Macheboeuf (1951) have found that penicillin inhibits the breakdown of guanosine by sensitive strains of Staph. aureus. Park & Johnson (1949) described the accumulation of labile phosphate compounds in Staph. aureus growing in the presence of penicillin, and Park (1952) identified three substances accumulating under these conditions; one of these is a derivative of uridine-5'-pyrophosphate and an N-acetylaminosugar, and the other two possess the same basic structure in combination with either L-alanine or a peptide containing L-lysine, Dglutamic acid and DL-alanine.