Lysis of bacterioids in the vicinity of the host cell nucleus in an ineffective (fix-) root nodule of soybean (Glycine max)

In nodules of Glycine max cv. Mandarin infected with a nod ⁺fix^- mutant of Rhizobium japonicum (RH 31-Marburg), lysis of bacteroids was observed 20 d after infection, but occurred in the region around the host cell nucleus, where lytic compartments were formed. Bacteroids, and peribacteroid membranes in other parts of the host cell remained stable until senescence (40d after infection). With two other nod⁺ fix^- mutants of R. japonicum either stable bacteroids and peribacteroid membranes were observed throughout the cell (strain 61-A-165) or a rapid degeneration of bacteroids without an apparent lysis (strain USDA 24) occurred. The size distribution of RH 31-Marburg-infected nodules exhibited only two maxima compared with four in wild-type nodules and nodule leghaemoglobin content was found to be reduced to about one half that of the wild type. The RH 31-Marburg-nodule type is discussed in relation to the stability of the bacteroids and the peribacteroid membrane system in soybean.     

Determination of deoxyribonucleic acid replication time in exponentially growing Escherichia coli B/r.

The time necessary to replicate the chromosome (C period) was measured in Escherichia coli B/r (ATCC 12407) and a low-thymine-requiring derivative of that strain. In the Thy- strain, C was measured as a function of growth rate and exogenous thymine concentration either from step-up or chloramphenicol experiments. In the Thy+ parental strain, C was measured only as a function of the growth rate and only by the chloramphenicol method. The C period was found to decrease with growth rate and, in the Thy- strain, the C period also decreased with increasing thymine concentration. It approached a value of approximately 37 min at high growth rates.     

Isolation of single-site Escherichia coli mutants deficient in thiamine and 4-thiouridine syntheses: identification of a nuvC mutant

A method is described to rapidly select and classify many independent near-UV irradiation-resistant Escherichia coli mutants, which include tRNA modification and RNA synthesis control mutants. One class of these mutants was found to be simultaneously deficient in thiamine biosynthesis and in the ability to modify uridine in tRNA to 4-thiouridine, known to be the target for near-UV irradiation. These mutants were found to be unable to make thiazole, a thiamine precursor. The addition of thiazole restores the thiamine deficiency but does not render the cells near-UV irradiation sensitive. In vitro studies on one of these mutants indicated a deficiency in protein factor C (nuvC), required for the 4-thiouridine modification of tRNA. In P1 transduction, the thiazole marker cotransduced with the histidine marker, which places the thiazole marker between 42 and 46 min on the E. coli chromosome map. Both thiamine production and 4-thiouridine production were resumed by 87% of the spontaneous reversions, suggesting a single-point mutation. Our results indicate that we have isolated nuvC mutants and that the nuvC polypeptide is involved in two functions, tRNA modification and thiazole biosynthesis.     

Control of RNA synthesis in Escherichia coli after a shift to higher temperature.

Parameters of RNA synthesis were measured after a temperature upshift in a pair of Escherichia coli B/r strains that are isogenic except for having relA and relA+ loci, to examine the cause for a reported anomaly in the correlation between guanosine tetraphosphate (ppGpp) and stable RNA (rRNA, tRNA) synthesis under such conditions. Two main results were: (i) the specific stable RNA gene activity (stable RNA per total RNA synthesis) correlated in the conventionally expected fashion with the level of ppGpp but was obscured by a nonspecific increase in the RNA chain elongation rate due to the higher temperature; (ii) the temperature upshift caused a transient reduction in the RNA polymerase activity (transcribing per total enzyme) that accounts for the previously observed oscillating RNA synthesis rate after a temperature shift.     

Rubidium—A possible essential trace element

The rubidium content of whole blood was estimated by instrumental neutron activation analysis. In 46 healthy children it amounts to {ie193-1} g/g dry weight. There was no difference between the values found for infants, toddlers, and school children. In 29 dietetically treated patients with phenylketonuria and maple-syrup-urine disease the values were significantly lower than in healthy children. During the first three months of diet therapy the rubidium levels remained in the lower range of the normal values, decreasing to about 60% of the mean of normal values later on. With increasing length of diet therapy these values tended to decrease. It remains questionable whether these decreased levels reflect only an induced biochemical phenomenon without biological importance, or whether they are the first signs of a deficiency syndrome.     

Multiple forms of phycoerythrin-545 from Cryptomonas maculata

Three multiple phycoerythrin-545 forms were purified from crude extracts of Cryptomonas maculata by preparative isoelectric focusing. The phycoerythrin forms are charge isomers with isoelectric points at 7.83, 5.05 and 4.84. The multiple pigment forms have similar molecular weights of 44500 daltons and are composed of subunits of unequal size in a 1:1 stoichiometry with molecular weights of () 9900 and () 15700 daltons, twice. The proposed quarternary structure of the native pigments is ()₂()₂.The charge differences of the phycoerthrins are caused by a charge heterogeneity of the light subunits, as revealed by urea gel electrophoresis. The chains of pigment form pI 7.83 had a greater electrophoretic mobility than those subunits of the acidic pigment forms pI 5.05 and pI 4.84.The phycoerythrin forms have an absorption spectrum with similar absorption maxima at 544 nm, but differ in the position of the long wavelength shoulders lying at 555 and 557 nm in the negatively charged pigment forms and at 560 nm for the phycoerythrin form with a pI at 7.83.The fluorescence emission spectra coincide in their asymmetrical shape with shoulders at about 620 nm; they slightly differ int he position of the emission maxima at 586 nm for the phycoerythrins with pIs at 4.84 and 5.05 and at 584 nm for phycoerythrin with pI at 7.83.Abbreviations PC phycocyanin - PE phycoerythrin - pI isoelectric point - SDS sodium dodecyl sulphate     

Escherichia coli ppGpp synthetase II activity requires spoT

Escherichia coli has two enzymes catalyzing the synthesis of guanosine tetraphosphate (ppGpp), designated ppGpp synthetase I (PSI = RelA) and II (PSII), whose activities are regulated differently. Until now, the gene for PSII had not been identified. Here, an E. coli relA1 strain that expresses lacZ from an rrnB P1 promoter was used to screen mutants with increased beta-galactosidase activity on 5-bromo-4-chloro-3-indoyl beta-D-galactoside indicator plates at 30 degrees C. About 15% of the mutants obtained in this manner had reduced levels of ppGpp at 30 degrees C and no detectable ppGpp at 43 degrees C. These mutants did not form colonies at 42 degrees C on minimal medium plates and had elevated ribosome concentrations and higher growth rates at 30 degrees C. Genetic mapping by phage P1 transduction and complementation analyses showed that the mutations were located in spoT and that they were recessive. Specific inhibition of SpoT-dependent ppGpp degradation activity with picolinic acid showed that two of the mutants tested were deficient in ppGpp synthesis activity. These results indicate that spoT is required for PSII activity, suggesting that spoT encodes both ppGpp degradation and synthesis activities and that these two functions can be affected independently by mutation.     

Biosynthetic pathways of Vibrio succinogenes growing with fumarate as terminal electron acceptor and sole carbon source

1. With fumarate as the terminal electron acceptor and either H₂ or formate as donor, Vibrio succinogenes could grow anaerobically in a mineral medium using fumarate as the sole carbon source. Both the growth rate and the cell yield were increased when glutamate was also present in the medium.
2. Glutamate was incorporated only into the amino acids of the glutamate family (glutamate, glutamine, proline and arginine) of the protein. The residual cell constituents were synthesized from fumarate.
3. Pyruvate and phosphoenolpyruvate, as the central intermediates of most of the cell constituents, were formed through the action of malic enzyme and phosphoenolpyruvate synthetase. Fructose-1,6-bisphosphate aldolase was present in the bacterium suggesting that this enzyme is involved in carbohydrate synthesis.
4. In the absence of added glutamate the amino acids of the glutamate family were synthesized from fumarate via citrate. The enzymes involved in glutamate synthesis were present.
5. During growth in the presence of glutamate, net reducing equivalents were needed for cell synthesis. Glutamate and not H₂ or formate was used as the source of these reducing equivalents. For this purpose part of the glutamate was oxidized to yield succinate and CO₂.
6. The α-ketoglutarate dehydrogenase involved in this reaction was found to use ferredoxin as the electron acceptor. The ferredoxin of the bacterium was reoxidized by means of a NADP-ferredoxin oxidoreductase. Enzymes catalyzing the reduction of NAD, NADP or ferredoxin by H₂ or formate were not detected in the bacterium.