Isolation and characterization of a mutant of Escherichia coli blocked in the synthesis of putrescine

Polyamine requirements of a conditional polyamine auxotroph of Escherichia coli

Escherichia coli MA-159 is deficient in agmatine ureohydrolase. After addition of exogenous arginine, the cellular putrescine content declines immediately and exponentially; however, the spermidine content remains normal for 3 h. The growth rate of such cultures, measured turbidometrically, slows gradually over many hours. Putrescine-depleted cultures grow especially slowly in media of low osmolarity, whereas nondepleted cultures grow at similar and rapid rates in media of either normal or low osmolarity. External osmolarity also affects the ability of various exogenous polyamines to stimulate growth of putrescine-depleted cultures. In medium of normal osmolarity, putrescine and spermidine both allow sustained rapid growth for many hours. In low osmolarity medium, putrescine allows sustained rapid growth, whereas cultures containing spermidine grow more slowly; this result cannot be explained by conversion of putrescine to spermidine, for cultures grown with exogenous putrescine contain smaller spermidine pools than do cultures grown with exogenous spermidine. Spermine greatly stimulates growth in medium of normal osmolarity; however, in medium of low osmolarity, spermine is much less effective and can block the action of putrescine. Several other polyamines have been studied in this system. These results confirm and expand previous reports that polyamines are necessary for growth of E. coli and suggest that putrescine may have a specific function during growth in media of low osmolarity.

Growth and macromolecular composition of a mutant of Escherichia coli during polyamine limitation

A mutant of Escherichia coli with reduced levels of biosynthetic arginine decarboxylase was isolated which required putrescine or spermidine for optimal growth. The stimulation of growth by putrescine was 1.5- to 3-fold depending upon the culture medium. Specificity studies supported the concept that the requirement was for spermidine or closely related polyamines, or for diamines which could be converted enzymatically to these compounds. The behavior of the macromolecular composition of the polyamine-starved cells appeared abnormal. The ribonucleic acid to protein and deoxyribonucleic acid to cell ratios in the starved cells were both higher than expected on the basis of their growth rate. The stable ribonucleic acid in the polyamine-limited cells appeared to be normal as judged from size distribution and degree of methylation. The relationship of these results to mechanisms for regulation of nucleic acid and protein synthesis in E. coli is discussed.

Regulation of macromolecular synthesis by putrescine in a conditional Escherichia coli putrescine auxotroph

Addition of putrescine to a slowly growing, polyamine-starved Escherichia coli K-12 mutant conditionally incapable of synthesizing putrescine causes the immediate stimulation of protein synthesis. After a period ranging from 60 to 105 min, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) syntheses are also stimulated and rapid cellular division begins. Chloramphenicol blocks this rapid cellular division, although addition of the specific DNA synthesis inhibitor, nalidixic acid, has no effect on cell division. By sucrose gradient analysis and diethylaminoethyl-cellulose chromatography, the proteins initially made in response to putrescine appear to be composed of many classes, including membrane-bound proteins. However, the synthesis of ribosomal subunits is not altered during this period. A possible role for putrescine in either the stimulation of messenger RNA transcription or in translation is suggested.

Polyamines in the synthesis of bacteriophage deoxyribonucleic acid. II. Requirement for polyamines in T4 infection of a polyamine auxotroph

Polyamine depletion produced by exogenous arginine in Escherichia coliK-12 cultures defective in agmatine ureohydrolase activity resulted in a marked inhibition of the rates of growth and nucleic acid synthesis. Addition of putrescine or spermidine to such depleted cultures restored the control rate of growth and nucleic acid accumulation. The omission of lysine resulted in a further decrease in the rates of growth and nucleic acid synthesis in polyamine-depleted cells. The addition of exogenous cadaverine increased the rates of growth and ribonucleic acid synthesis to those observed in lysine-supplemented cultures, suggesting that lysine or a derivative of lysine serves a function similar to cadaverine. Addition of lysine to polyamine-depleted cultures at neutral pH results in the synthesis of cadaverine and a new spermidine analogue, both containing lysine carbon. This new metabolite has been isolated and identified as N-3-aminopropyl-1, 5-diaminopentane. T4D infection of the polyamine-depleted mutant resulted in a very low rate of DNA synthesis and phage maturation. The addition of putrescine or spermidine 15 min before infection restored phage DNA synthesis and phage maturation to control rates, i.e., rates observed in infected cells grown in the absence of arginine.

Polyamine stimulation of nucleic acid synthesis in an uninfected and phage-infected polyamine auxotroph of Escherichia coli K12 (arginine-agmatine ureohydrolase-putrescine-spermidine-lysine-cadaverine)

The addition of arginine to cultures of Escherichia coli K12 deficient in agmatine ureohydrolase (EC 3.5.3.7) results in polyamine depletion and a striking inhibition of nucleic acid accumulation and growth. The omission of lysine from these cultures leads to a further decrease in growth rate and nucleic acid synthesis. In arginine-inhibited cells the addition of putrescine or spermidine, in the presence or absence of lysine, restores the control rate of growth and nucleic acid accumulation. Under the same conditions of arginine inhibition in the absence of lysine, the addition of cadeverine alone stimulates growth rate and RNA synthesis. The addition of lysine to polyamine-depleted cultures results in cadaverine production and in the appearance of a new spermidine analogue, containing lysine carbon. The new compound has been identified as N-3-aminopropyl-1,5-diaminopentane. Infection of this arginine-inhibited, polyamine-depleted mutant with T(4)D results in markedly decreased amounts of DNA accumulation, as compared to infected cells uninhibited by arginine. Supplementation of arginine-inhibited infected cells by putrescine or spermidine restores DNA synthesis to the uninhibited level.

Arginaseless Neurospora: genetics, physiology, and polyamine synthesis

Four arginaseless mutants of Neurospora crassa have been isolated. All carry mutations which lie at a single locus, aga, on linkage group VIIR. A study of aga strains shows the arginase reaction to be the major, perhaps the only, route of arginine consumption in Neurospora other than protein synthesis. Ornithine-delta-transaminase, the second enzyme of the arginine catabolic pathway, is present and normally inducible by arginine in aga strains, and ornithine transcarbamylase, an enzyme of arginine synthesis, also has normal activity. Arginine inhibits the growth of aga strains. The inhibition can be reversed by spermidine, putrescine (1,4-diaminobutane), or ornithine. The results suggest that ornithine is the major source of the putrescine moiety of polyamines in Neurospora, and that putrescine is an essential growth factor for this organism. The inhibition of aga strains by arginine can be attributed to feedback inhibition of ornithine synthesis by arginine, combined with the complete lack of ornithine normally provided by the arginase reaction.

Isolation of conditionally putrescine-deficient mutants of Escherichia coli

Mutants defective in the conversion of arginine to putrescine were found by screening clones from mutagenized cultures for inability to produce urea during growth in arginine-supplemented media. Two partially blocked mutants were isolated; one was deficient in arginine decarboxylase and the other was deficient in agmatine ureohydrolase. As predicted from the pattern of putrescine synthesis in Escherichia coli, these mutants were conditionally putrescine-deficient. When grown in either minimal or ornithine-supplemented media, conditions which lead to preferential utilization of the ornithine to putrescine pathway, the mutants had normal intracellular polyamine levels. However, when the mutants were placed in arginine-supplemented media, the level of intracellular putrescine was lowered markedly. Under conditions where intracellular putrescine was 1% of normal, the doubling time of the mutants was increased approximately 10%. The putrescine-deficient mutants had wild-type morphology, normal levels of protein and ribonucleic acid (RNA), and stringent amino acid control of RNA synthesis.