Metabolism of glutamic acid in a mutant of Escherichia coli

Vender, Joyce (Indiana University, Bloomington), Kunthala Jayaraman, and H. V. Rickenberg. Metabolism of glutamic acid in a mutant of Escherichia coli. J. Bacteriol. 90:1304-1307. 1965.-A mutant strain of Escherichia coli W1485 was selected for its ability to utilize glutamic acid as the sole source of carbon. Growth of the mutant on glutamic acid led to the repression of glutamic acid dehydrogenase formation. The mutant differed from the wild-type strain in that glutamic decarboxylase activity was absent from the mutant under conditions of growth which supported the formation of this enzyme in the parent strain. Evidence is presented which suggests that loss of the decarboxylase activity results in the acquisition of the ability to utilize glutamic acid as sole source of carbon; a pathway of glutamate utilization via transamination is proposed.     

Metabolism of 6-aminonicotinic acid in Escherichia coli.

A late-log-phase culture of an Escherichia coli nadB pncA double mutant took up 6-[7-14C]aminonicotinic acid and excreted 6-[14C]aminonicotinamide. This mutant also accumulated intracellularly several radioactive compounds which have been tentatively identified as 6-amino analogs of compounds in the pyridine nucleotide cycle. It is concluded that 6-aminonicotinamide and 6-aminonicotinic acid probably exert at least a portion of their bacteriostatic effects by being metabolized, by the enzymes of the pyridine nucleotide cycle, to 6-aminonicotinamide adenine dinucleotide and 6-aminonicotinamide adenine dinucleotide phosphate. These compounds are not electron acceptors and are known inhibitors of some pyridine nucleotide-linked dehydrogenases.     

Macromolecular syntheses in an Escherichia coli adk mutant

Preferential inhibition by high temperatures of synthesis of newly induced enzymes in Escherichia coli K-12 CR341T28 adk is only apparent; syntheses of all macromolecules cease simultaneously.     

Description of an incompatibility mutant of Escherichia coli

A mutant Hfr strain of Escherichia coli which has an impaired incompatibility function but is normal for other F factor functions has been isolated. This Inc(-) Hfr permits the maintenance and transfer of both the integrated F factor and an F' factor. F' factors have been isolated from the integrated F factor of the Inc(-) Hfr strain. When these episomes were tested in matings with Hfr or F' strains, they did not differ in any observed way from wild-type F' factors.     

Conditional-lethal deoxyribonucleic acid ligase mutant of Escherichia coli.

A new Escherichia coli deoxyribonucleic acid (DNA) ligase mutant has been identified among a collection of temperature-sensitive DNA replication mutants isolated recently (Sevastopoulos, Wehr, and Glaser, Proc. Natl. Acad. Sci. U.S.A. 74:3485-3489, 1977). At the nonpermissive temperature DNA synthesis in the mutant stops rapidly, the DNA is degraded to acid-soluble material, and cell death ensures. This suggests that the mutant may be among the most ligase-deficient strains yet characterized.     

Growth of an Escherichia coli mutant deficient in respiration

An Escherichia coli mutant deficient in genes for heme biosynthesis grew in medium of initial pH 8 containing 1% tryptone and glucose under aerobic growth conditions, and its doubling time was approximately 60 min at 37°C. The growth rate was not increased under O₂-limiting conditions. When the mutant was grown in medium of initial pH 6, growth stopped at the middle of the exponential growth phase. This could be overcome and the growth yield increased by the addition of 20 mM lysine to the growth medium. Lysine did not prevent the decrease in the medium pH as growth proceeded, making it unlikely that lysine decarboxylation stimulates growth by the alkalinization of the medium. These results indicate that respiration is not obligatory for growth under aerobic conditions, but growth without respiration at low pH requires a large amount of lysine.     

Oxygen sensitivity of an Escherichia coli mutant.

Genetic evidence indicates that Oxys-6, an oxygen-sensitive mutant of Escherichia coli AB1157, is defective in the region of the hemB locus. Oxys-6 is capable of growth under aerobic conditions only if cultures are initiated at low-inoculum levels. Aerobic liquid cultures are limited to a cell density of 10(7) cells per ml by the accumulation of a metabolically produced, low-molecular-weight, heat-stable material in complex organic media. Both Oxys-6 and AB1157 cells produce the material, but only aerobic cultures of the mutant are inhibited by it. The material is produced by both intact cells and cell extracts in complex media. This reaction also occurs when the amino acid L-lysine is substituted for complex media.     

Isolation of an Escherichia coli mutant defective in cytochrome biosynthesis

Abstract A pleiotropic mutant of Escherichia coli affected in cytochrome biosynthesis was detected by anaerobic screening on a solid medium containing triphenyltetrazolium. When grown anaerobically on glycerol, nitrate and Casamino acids, this mutant exhibited a level of soluble cytochrome c ₅₅₂ which was ten times higher than that found in wild-type cells. The level of membrane-bound cytochrome b and the activity of nitrate reductase were about half the normal level. The mutant grew aerobically on succinate or d,l -lactate at a greatly reduced rate. The mutation impairing the growth ability at the locus sox (succinate oxidation) is also responsible for the deficiency of cytochrome b , nitrate reductase and formate dehydrogenase. Mapping by transduction placed sox at 86.7 min on the chromosome, very close to the glnA locus. Genetic analysis also indicated that the elevated level of cytochrome c ₅₅₂ was the result of a separate mutation, the location of which is yet to be determined.     

S-Methylmethionine Metabolism in Escherichia coli

Selenium-accumulating Astragalus spp. contain an enzyme which specifically transfers a methyl group from S-methylmethionine to the selenol of selenocysteine, thus converting it to a nontoxic, since nonproteinogenic, amino acid. Analysis of the amino acid sequence of this enzyme revealed that Escherichia coli possesses a protein (YagD) which shares high sequence similarity with the enzyme. The properties and physiological role of YagD were investigated. YagD is an S-methylmethionine: homocysteine methyltransferase which also accepts selenohomocysteine as a substrate. Mutants in yagD which also possess defects in metE and metH are unable to utilize S-methylmethionine for growth, whereas a metE metH double mutant still grows on S-methylmethionine. Upstream of yagD and overlapping with its reading frame is a gene (ykfD) which, when inactivated, also blocks growth on methylmethionine in a metE metH genetic background. Since it displays sequence similarities with amino acid permeases it appears to be the transporter for S-methylmethionine. Methionine but not S-methylmethionine in the medium reduces the amount of yagD protein. This and the existence of four MET box motifs upstream of yfkD indicate that the two genes are members of the methionine regulon. The physiological roles of the ykfD and yagD products appear to reside in the acquisition of S-methylmethionine, which is an abundant plant product, and its utilization for methionine biosynthesis.     

Gluconate Metabolism in Escherichia coli

On the basis of information available in the literature, gluconate dissimilation in Escherichia coli is thought to occur via the hexose monophosphate pathway. Evidence is presented in this study that gluconate is catabolized in this organism via an inducible Entner-Doudoroff pathway. This evidence is based on chromatographic examination of end products produced from (14)C-labeled gluconate or glucose, distribution of (14)C in the carbon atoms of pyruvate formed from specifically labeled (14)C-glucose and (14)C-gluconate, and the ability of cell-free extracts to produce pyruvate from 6-phosphogluconate. Degradation of gluconate by an Entner-Doudoroff pathway occurred simultaneously with a glycolytic cleavage of glucose. A relationship between gluconate-induced, Entner-Doudoroff pathway activity and catabolism of glucose in Escherichia coli and other bacterial species is discussed.