The lethality of streptomycin and the stimulation of RNA synthesis in the absence of protein synthesis

Streptomycin revisited: molecular action in the microbial cell

The key event for antimicrobial action begins when streptomycin binds to the 30S subunit (S12 protein) of a ribosome. Lysine 42 and lysine 87 are involved. It is proposed that antagonism of acetyl coenzyme A carboxylase by streptomycin results in faulty fatty acids, lipids and derivatives marked exclusively for cell membrane synthesis. Streptomycin-sensitive growing cells are fatally wounded when defective membranes leak K(+) ions, then amino acids, nucleotides, oligonucleotides and proteins as increasing amounts of streptomycin enter the cell.

Inhibition of DNA replication initiation by aminoglycoside antibiotics

The reinitiation of DNA replication induced by a temperature shift in a dnaC(Ts) mutant of Escherichia coli was markedly inhibited by aminoglycoside antibiotics around the MIC in a short period. Protein synthesis continued for several minutes after the addition of aminoglycosides but was immediately blocked by chloramphenicol, suggesting that the inhibition of initiation of replication by aminoglycosides is not a secondary effect due to the interruption of protein synthesis. Aminoglycosides did not significantly affect RNA synthesis, suggesting that primer RNA synthesis for DNA initiation is not blocked by the agents. The lethal action of habekacin was observed simultaneously with the inhibition of DNA reinitiation. DNA elongation demonstrated with a dnaE(Ts) mutant or toluene-treated cells of a polA mutant was not significantly affected by aminoglycosides. The oriC-membrane complex formation was markedly interrupted by habekacin in the dnaC(Ts) mutant, and the in vitro reconstitution of the oriC-membrane complex was completely blocked by aminoglycosides. The present studies show that aminoglycosides block initiation of DNA replication and suggest that the inhibition is caused by the interruption of oriC-membrane attachment.

Effects of aminoglycoside antibiotics on the coupling of protein and RNA syntheses in Escherichia coli

The interdependency of protein and RNA syntheses was studied comparatively in bacteria confronted with amino acid starvation or treated separately with various aminoglycoside antibiotics. By contrast with the concomitant inhibition of macromolecular syntheses in cells deprived of an essential amino acid, RNA production was found to continue in drug-treated cells while protein synthesis was arrested. Such uncoupling process was also observed in bacteria subjected simultaneously to amino acid starvation and treatment with certain antibiotics (neomycin, gentamicin, spectinomycin and kasugamycin) but not with others (streptomycin and kanamycin). These results were related to the intracellular concentration of guanosine polyphosphates, ppGpp and pppGpp. They were discussed in terms of interaction of aminoglycosides with ribosomes.

Susceptibility of Actinomyces to cephalosporins and lincomycin

The effects of streptomycin on the synthesis of ribonucleic acid (RNA) and guanosine-3′-diphosphate-5′-diphosphate have been examined in the isogenic strains CP78 (rel⁺) and CP79 (rel−). In the absence of the required amino acids arginine, leucine, or threonine, streptomycin stimulates RNA synthesis in CP78 and this stimulation coincides with cell death. However, in the absence of histidine, also a required amino acid, streptomycin kills the cells without stimulation of RNA synthesis above that which occurs in the absence of streptomycin. In all of these instances, guanosine-3′-diphosphate-5′-diphosphate levels vary inversely with RNA synthesis, decreasing when a stimulation of RNA synthesis occurs. Streptomycin has little effect on guanosine-3′-diphosphate-5′-diphosphate levels in CP78 in the absence of histidine. Another histidine auxotroph, 15 T⁻H⁻U⁻ (rel⁺), does show streptomycin-stimulated synthesis of RNA which is coincident with cell death. CP79 (rel⁻) is 10 times more susceptible to streptomycin than CP78 and streptomycin causes an inhibition of the relaxed synthesis of RNA. The greater susceptibility of CP79 may be due to a greater initial uptake of streptomycin by CP79.

Osmotic sensitivity in Staphylococcus aureux induced by streptomycin

Differential light-scattering measurements of Staphylococcus aureus cultures were made before and after treatment with streptomycin. Changes were observed in the light-scattering characteristics of streptomycin-treated sensitive cells within 5 min after suspension in a hypotonic solution. No changes were observed with a resistant strain of cells nor with either strain in an isotonic solution. The observed effects occur more slowly when the cells are growing slowly. The physical effects consonant with the changes in the light-scattering curves are a broadening of the cell size distribution, a slight reduction in mean size, and the appearance of clumps or debris. We conclude that streptomycin rapidly alters the selective permeability of the cell membrane and makes the cells susceptible to increased osmotic stresses.

Effects of streptomycin on plastids in dividing Euglena

The plastids of dividing Euglena cells growing in the light in the presence of streptomycin decreased in length after a lag period of seven generations. The typical structure of the chloroplast was lost after a similar lag period. This loss of structure did not follow a regular pattern. After 11 generations the plastids resembled normal proplastids of dark-grown cells. Initial chlorophyll loss of treated cells was slow, but after 3 generations the rate of loss was about 0.5/generation, indicating a cessation of synthesis and a dilution among the progeny.

The action of streptomycin in a mutant of Escherichia coli with increased sensitivity to the antibiotic

A mutant of Escherichia coli with increased sensitivity to streptomycin has been studied. This strain differed from a normal str(s) strain in that streptomycin produced inhibition of protein synthesis and loss of viability with almost no lag period. Chloramphenicol protected a normal str(s) strain but not the mutant against the bactericidal action of streptomycin. The results obtained support the idea that access of streptomycin to its site of action in a normal cell is restricted, and that this restriction, which is much less effective in the mutant, probably involves a permeability barrier. Comparison of the inhibition of protein synthesis by streptomycin with concomitant changes in the distribution of polyribosomes in both strains suggested that the antibiotic can directly inhibit the translation of mRNA.

T6r+-induced proteins and nucleic acids in Escherichia coli infected in the presence of streptomycin

Streptomycin does not strongly inhibit T-even phage multiplication in the streptomycin-susceptible polyauxotroph, Escherichia coli strain T(-)H(-)U(-). The relatively slight inhibition, observed earlier, on production of late proteins has now been studied further. The phage-induced ribonucleic acid, synthesized in T6 phage infection in the presence of streptomycin, has been characterized by its base composition, size distribution, and behavior in hybridization tests. Comparison of these properties to those of control samples, taken during either early or late periods of infection, have not shown any significant differences. Phage-induced proteins, synthesized at different times during infection, were studied by disc-gel electrophoresis. Staining and autoradiography of the patterns of pulse-labeled proteins, formed in the absence and presence of the antibiotic showed only slight quantitative changes in the appearance of early proteins. More marked quantitative effects were detected later in infection. Nevertheless, changes in the mobilities of the different proteins were not observed in the streptomycin-treated cultures at any time after infection, suggesting the absence of gross misreading sufficiently great to alter the distinctive electrophoretic patterns of the extracts. Cells infected and incubated in the presence of the antibiotic were found to contain intact virus particles, as shown by electron microscopy. Such infected cells contained extensive deoxyribonucleic acid pools and did not develop the rounded nucleoids with enclosed dense bodies characteristic of the lethal action of the antibiotic. On the other hand, infected bacteria previously exposed to lethal concentrations of streptomycin were unable to synthesize the early enzymes, deoxycytidylate (dCMP) hydroxymethylase and dihydrofolate reductase, or to make phage deoxyribonucleic acid and phage. Such previously killed cells contained the rounded and clotted nucleoids and were unable to unravel this pathological structure after phage infection.

Serum-mediated immune cellular responses to Brucella melitensis. I. Role of a macrophage-stimulating factor in promoting ingestion of Brucella by streptomycin-protected cells

Injection of rabbits with living Brucella melitensis Rev I induced the appearance of a macrophage-stimulating-factor (MSF) in the sera of these animals. MSF was involved in ingestion of bacilli, hastening the formation of protected loci as measured by the addition of lethal amounts of dihydrostreptomycin. When sufficient time had been allowed for effective ingestion, streptomycin had little effect. This in turn allowed for multiplication of bacilli intracellularly in the presence of 5 to 250 mug of drug per ml. MSF mediated more effective ingestion by both immune and normal macrophages. Under such conditions, there was little, if any, intracellular growth restriction by macrophages from immune animals. The activity appeared within the first 5 days after injection with 10(9) organisms and was present for several months. Three weeks after injection, the activity of serum was partially heat-labile. All activity was removed by absorption with heat-killed or living Rev I cells, suggesting that a specific globulin is concerned.

Polyamines and the accumulation of ribonucleic acid in some polyauxotrophic strains of Escherichia coli

The cellular accumulations of polyamines and ribonucleic acid (RNA) were compared in the polyauxotrophic mutants of Escherichia coli strain 15 TAU and E. coli K-12 RC(re1) met(-) leu(-). Putrescine, spermidine, and their monoacetyl derivatives were the main polyamines in both strains, when grown in glucose-mineral medium. No significant degradation of either (14)C-putrescine or (14)C-spermidine was found in growing cultures of strain 15 TAU, which requires thymine, arginine, and uracil for growth. Experiments with this organism showed that in a variety of different incubation conditions, which included normal growth, amino acid starvation, inhibition by chloramphenicol or streptomycin, or thymine deprivation, a close correlation was seen between the intracellular accumulation of unconjugated spermidine and RNA. In the presence of arginine, the antibiotics stimulated the production of putrescine and spermidine per unit of bacterial mass. Deprivation of arginine also resulted in an increase in the production of putrescine per unit of bacterial mass, most of which was excreted into the growth medium. However, in this system the antibiotics reduced the synthesis of putrescine. Furthermore, streptomycin caused a rapid loss of cellular putrescine into the medium. The latter effect was not seen in anaerobic conditions or in a streptomycin-resistant mutant of 15 TAU. Methionine added to the growth medium of growing TAU not only markedly increased the total production of spermidine, but also increased both the intracellular concentration of spermidine and the accumulation of RNA. Exogenous spermidine extensively relaxed RNA synthesis in amino acid-starved cultures of 15 TAU. Analysis in sucrose density gradients showed that the RNA accumulated in the presence of spermidine was ribosomal RNA. Cells of E. coli K-12 RC(rel) met(-) leu(-), grown in a complete medium, had approximately the same ratio of free spermidine to RNA as did strain 15 TAU. However, the relaxed strain showed a much lower ratio of putrescine to spermidine than the stringent 15 TAU. Omission of methionine stopped spermidine synthesis and markedly increased both the intracellular accumulation and the total production of putrescine. It seems that a high intracellular level of spermidine acts as a feedback inhibitor in the biosynthesis of putrescine in this strain. The hypothesis that the intracellular concentration of polyamines may participate in the control of the synthesis of ribosomal RNA in bacteria is discussed.

Streptomycin and infection of Escherichia coli by T6r+ bacteriophage

Freda, Celia E. (University of Pennsylvania School of Medicine, Philadelphia), and Seymour S. Cohen. Streptomycin and infection of Escherichia coli by T6r(+) bacteriophage. J. Bacteriol. 92:1670-1679. 1966.-The thymineless, histidineless, uracil-less Escherichia coli 15 THU was shown to be sensitive to streptomycin, dying in patterns comparable to that of strain 15 TAU in the presence or absence of the required amino acid histidine. In the absence of histidine, the antibiotic stimulated ribonucleic acid (RNA) synthesis without a detectable inhibition or stimulation of deoxyribonucleic acid (DNA) synthesis. In the presence of streptomycin (40mug/ml) under conditions of multiple infection with T6r(+), lysis of THU occurred 1 hr earlier than did the control, having produced about one-third as much DNA and phage as did the control. In the absence of histidine, thereby preventing synthesis of phage DNA, accumulation of virus-induced RNA was similar for about 30 min in control and streptomycin-treated systems. In the presence of the antibiotic, however, the infected cells accumulated about 50 to 70% more RNA than did the control after 90 min. Nevertheless, the turnover of RNA was not detectably affected by streptomycin. The rate of production and final amount of deoxycytidylate hydroxymethylase, as well as the cut off time of synthesis of this enzyme, were scarcely affected by streptomycin. The beginning of DNA synthesis was delayed about 3 to 4 min by the antibiotic. The incorporation of histidine in infected cells was unaffected for 10 min and was only about 10% less than the control at 70 min. Lysozyme production began at about 10 min in control and antibiotic-treated systems, continued at essentially similarly increasing rates for 20 min, but stopped abruptly in the streptomycin-treated cells despite continuing protein synthesis. With the exception of lysozyme, the production of phage-specific polymers in a streptomycin-sensitive bacterium was only slightly affected by the antibiotic.

Nature of ribonucleic acid stimulated by streptomycin in the absence of protein synthesis

Freda, Celia E. (University of Pennsylvania School of Medicine, Philadelphia), and Seymour S. Cohen. Nature of ribonucleic acid stimulated by streptomycin in the absence of protein synthesis. J. Bacteriol. 92:1680-1688. 1966.-The ribonucleic acid (RNA) synthesized in a thymineless, arginineless, uracil-less Escherichia coli strain 15 in the absence of arginine was characterized by sucrose density gradient centrifugation. About 60% of this RNA had sedimentation rates in the range between 4S and 16S, and the remainder was comprised of the 23S and 16S ribosomal components. On addition of streptomycin for 1 hr in the absence of the amino acid, there was an inhibition of synthesis of material of 4S to 16S, whereas 16S RNA was slightly stimulated. Between 1 and 3 hr after addition of the antibiotic, during the precipitous killing of the bacteria in the arginine-deficient culture, the synthesis of 16S ribosomal RNA was specifically and sharply stimulated.