Frequency-dependent effects of ELF magnetic field on chromatin conformation in Escherichia coli cells and human lymphocytes.

The effects of magnetic fields of extremely low frequency (ELF, 21 microT r.m.s.) on cells of different Escherichia coli K12 strains and human lymphocytes were studied by the method of anomalous viscosity time dependence (AVTD). Within the frequency range of 6-24 Hz, two resonance-type frequency windows with maximal effects at 9 Hz and 16 Hz were observed in response of GE499 strain. Only one frequency window with maximum effect at 8.5 Hz was found for GE500 cells. These data along with previously obtained for two other E. coli strains, AB1157 and EMG2, indicate that frequency windows are dependent on genotype of cells exposed to ELF. Resonance-type effects of ELF were also observed in human lymphocytes in frequency windows around 8 and 58 Hz. These ELF effects differed significantly between studied donors, but were well reproducible in independent experiments with lymphocytes from the same donors. The frequency windows in response of E. coli strains and human lymphocytes to ELF significantly overlapped suggesting that the same targets may be involved in this response. We compared the frequency windows with predictions based on the ion cyclotron resonance (ICR) model and the magnetic parametric resonance model. These models predicted effects of ELF magnetic fields at the 'cyclotron' frequencies of some ions of biological relevance. According to the ICR model, ELF effects should be also observed at harmonics of cyclotron frequencies and, contrary, parametric resonance model predicted effects at subharmonics. While we observed coincidence of each experimental resonance frequency with predictions of one of these two models, all experimentally defined effective frequency windows were in good agreement with relatively narrow frequency ranges of both harmonics and subharmonics for natural isotopes of Na, K, Ca, Mg, and Zn ions. The experimental data support idea that both harmonics and subharmonics of several biologically important ions are involved in frequency-dependent ELF effects in cells of different types.     

Frequency-dependent effects of ELF magnetic field on chromatin conformation in Escherichia coli cells and human lymphocytes

The effects of magnetic fields of extremely low frequency (ELF, 21 μT r.m.s.) on cells of different Escherichia coli K12 strains and human lymphocytes were studied by the method of anomalous viscosity time dependence (AVTD). Within the frequency range of 6–24 Hz, two resonance-type frequency windows with maximal effects at 9 Hz and 16 Hz were observed in response of GE499 strain. Only one frequency window with maximum effect at 8.5 Hz was found for GE500 cells. These data along with previously obtained for two other E. coli strains, AB1157 and EMG2, indicate that frequency windows are dependent on genotype of cells exposed to ELF. Resonance-type effects of ELF were also observed in human lymphocytes in frequency windows around 8 and 58 Hz. These ELF effects differed significantly between studied donors, but were well reproducible in independent experiments with lymphocytes from the same donors. The frequency windows in response of E. coli strains and human lymphocytes to ELF significantly overlapped suggesting that the same targets may be involved in this response. We compared the frequency windows with predictions based on the ion cyclotron resonance (ICR) model and the magnetic parametric resonance model. These models predicted effects of ELF magnetic fields at the ‘cyclotron’ frequencies of some ions of biological relevance. According to the ICR model, ELF effects should be also observed at harmonics of cyclotron frequencies and, contrary, parametric resonance model predicted effects at subharmonics. While we observed coincidence of each experimental resonance frequency with predictions of one of these two models, all experimentally defined effective frequency windows were in good agreement with relatively narrow frequency ranges of both harmonics and subharmonics for natural isotopes of Na, K, Ca, Mg, and Zn ions. The experimental data support idea that both harmonics and subharmonics of several biologically important ions are involved in frequency-dependent ELF effects in cells of different types.     

Cell density dependent response of E. Coli cells to weak ELF magnetic fields

The effects of weak magnetic fields of extremely low frequency (ELF) on E. coli K12 AB1157 cells were studied by the method of anomalous viscosity time dependencies (AVTD). E. coli cells at different densities within a range of 5 × 10⁵–10⁹ cell/ml were exposed to ELF (sinusoidal, 30 μT peak, 15 min) at a frequency of 9 Hz. A transient effect with maximum 40–120 min after exposure was observed. Kinetics of the per-cell-normalised ELF effects fitted well to a Gaussian distribution for all densities during exposure. A maximum value of these kinetics and a time for this maximum were strongly dependent on the cell density during exposure. These data suggest a cell-to-cell interaction during response to ELF. Both dependencies had three regions close to a plateau within the ranges of 3 × 10⁵ − 2 × 10⁷ cell/ml, 4 × 10⁷ − 2 × 10⁸ cell/ml and 4 × 10⁸–10⁹ cell/ml and two rather sharp transitions between these plateaus. The effect reached a maximum value at a density of 4 × 10⁸ cell/ml. Practically no effect was observed at the lowest density of 3 × 10⁵ cell/ml. The data suggested that the ELF effect was mainly caused by a secondary rather than a primary reaction. The filtrates from exposed cells neither induced significant AVTD changes in unexposed cells nor increased the ELF effect when were added to cells before exposure. The data did not provide evidence for significant contribution of stable chemical messengers, but some unstable compounds such as radicals could be involved in the mechanism of cell-to-cell interaction during response to ELF. The results obtained were also in accordance with a model based on an re-emission of secondary photons during resonance fluorescence. Bioelectromagnetics 19:300–309, 1998. © 1998 Wiley-Liss, Inc.     

Cooperative Response of Escherichia Coli Cells to the Resonance Effect of Millimeter Waves at Super Low Intensity

Cells of Escherichia coli K12 AB1157 were irradiated with millimeter waves (MMW) within the power density (PD) range of 10^?20 to 10 ⁴ W/cm². MMW were applied for 0.5–70 min at 51.76 GHz or 41.32 GHz at which, as had been shown earlier, MMW resonantly changes the genome conformational state (GCS) of E. coli K12 AB1157 cells. The changes in the GCS were tested with the method of anomalous viscosity time dependence (AVTD). It was demonstrated that the resonance effect of MMW manifests itself at PD up to 10^?19 W/cm². Dependences of MMW effect on power density and time of exposure proved to have distinct characteristics when cells are irradiated during the logarithmic or stationary phases of the culture's growth. It was found that the resonance effect of MMW on the GCS of E. coli cells at the early stationary phase changes the developmental dynamics of the irradiated culture. It was established for the first time that the magnitude of the resonance MMW effect depends on the concentration of irradiated cells. An analysis of the results indicates an electromagnetic rather than diffusion nature of the cells' cooperative responses to millimeter waves.     

Site-specific mutagenesis in cells with normal DNA repair systems: transitions produced from DNA carrying a single O6-alkylguanine.

This paper describes a systematic study of transition frequencies produced in vivo when a homologous series of O6-alkylguanine residues located at a preselected position in gene G of phi X174 form I' DNA (double-stranded, circular, covalently-closed, relaxed) is transfected into spheroplasts from two strains of Escherichia coli having normal DNA repair systems. Mutant frequencies were measured as percent of total phage produced by single bursts. The results are: (A) Synthetic DNA without any alkyl group gave a transition frequency of 0.02%. (B) In E. coli AB1157, the frequencies fall into two groups depending on the alkyl group: methyl and ethyl, 8-11%; n-propyl and n-butyl approximately 0.9%. (C) The average transition frequencies were higher in AB1157 than in C600. These data demonstrate that a single O6-alkylguanine residue can produce a specific transition at significant frequencies in cells with normal repair systems and that the mutant frequency depends upon the nature of the alkyl group and the cell type.     

RCI-1, a GSH-deficient mutant ofEscherichia coli B: Response to oxidants and thiol-reacting compounds

The concentration of glutathione (GSH) in bacteria is many-fold less than in mammalian cells except forEscherichia coli, where the GSH level is similar to that of mammalian tissues. On the basis of our observation that GSH in a B strain, ATCC 29682, was reduced (>80%) by exposure to oxidants while a K-12 strain (AB 1157) was minimally affected (<20%), we constructed a B strain GSH-deficient mutant that exhibited antioxidant enzyme activities similar to the wild strain. We successfully transduced thegsh A:: Tn10Km allele from JTG-10, a GSH-deficient K-12 strain, to ATCC 29682, the GSH-sufficient B strain. Compared with ATCC 29682, the growth of the GSH-deficient B mutant, designated RCI-1, was more sensitive to the presence of thiol-reactive chemicals. However, no difference was found between GSH-sufficient and -deficient strains in lethality following exposure to the same thiol-reactive chemicals. Thus, GSH inE. coli B is important in maintaining growth in the presence of oxidants but does not affect oxidant lethality.     

Lethal effects of pyrimidine dimers induced at 365 nm in strains of E. coli differing in repair capability

Photoreactivation (PR) after 365-nm inactivation was measured in four strains of Escherichia coli differing in repair capability. Photoreactivation was observed in the recA strains K12 and AB2480 and K12 AB2463 indicating a significant role of pyrimide dimers in the lethal action of 365-nm radiation in these strains. Significant PR was not observed in the uvrA strain, K12 AB1886, or in the repair proficient strain, K12 AB1157, after 265-nm inactivation. Biological evidence indicated that stationary phase cells had not lost the capacity for photo-enzymatic repair after fluences of 365-nm radiation of 2 × 10⁶ J/m⁻² or less. It is proposed that pyrimidine dimers, although induced, are not significant 365-nm lethal lesions in uvrA and wild-type strains because of their efficient dark repair.     

Escherichia coli K-12 mutants with enhanced resistance to ionizing radiation. IV. Recombination characteristics of Gamr mutants

In the radiation-resistant Gamr444 mutant the inheritance frequency of long F' episomes ORF1 (purE+ tsx+ procC+ lac+) and F'14 (ilv+--argE+) is lower, and the frequencies of chromosome mobilization and integrative suppression of temperature-sensitive dnaA46 mutation by the sex factor F are much higher than those in the wild-type strain AB1157 and another radiation-resistant mutant Gamr445. In this respect, the mutant Gamr444 is very similar to the recRC sbcB mutant (RecF-pathway of recombination).     

Plasmid control of recombination in E. coli K 12

Summary The recombination proficiency of three recipient strains of Escherichia coli K 12 carrying different plasmids was investigated by conjugal mating with Hfr Cavalli. Some plasmids (e.g. R1drd 19, R6K) caused a marked reduction in the yield of recombinants formed in crosses with Hfr but did not reduce the ability of host strains to accept plasmid F104. The effect of plasmids on recombination was host-dependent. In Hfr crosses with AB1157 (R1-19) used as a recipient the linkage between selected and unselected proximal markers of the donor was sharply decreased. Plasmid R1-19 also decreased the yield of recombinants formed by recF, recL, and recB recC sbcA mutants, showed no effect on the recombination proficiency of recB recC sbcB mutant, and increased the recombination proficiency of recB, recB recC sbcB recF, and recB recC sbcB recL mutants. An ATP-dependent exonuclease activity was found in all tested recB recC mutants carrying plasmid R1-19, while this plasmid did not affect the activity of exonuclease I in strain AB1157 and its rec ^– derivatives. The same plasmid was also found to protect different rec ^– derivatives of the strain AB1157 against the lethal action of UV light. We suppose that a new ATP-dependent exonuclease determined by R1-19 plays a role in both repair and recombination of the host through the substitution of or competition with the exoV coded for by the genes recB and recC.     

Enhancement by cysteamine of N-methyl-N-nitrosourea mutagenesis in E. coli

Cysteamine (MEA) is comutagenic to methylnitrosourea (MNU) in E. coli AB 1157 but not in the nonadaptable mutant derivative ada-6 of that strain. The comutagenic action of MEA was eliminated by cysteine at low concentrations, which also lowered mutation frequencies in AB1157 but not in ada-6. In model experiments it was shown that cysteine counteracted the inhibition by MEA of beta-galactosidase induction in both bacterium strains. The comutagenic action of MEA is interpreted as being due to an inhibition of induction of methyltransferase during treatment with MNU.     

A plasmid carrying mucA and mucB genes from pKM101 in Haemophilus influenzae and Escherichia coli.

The plasmid pMucAMucB, constructed from the Haemophilus influenzae vector pDM2, and a similar plasmid, constructed from pBR322, increased the survival after UV irradiation of Escherichia coli AB1157 with the umu-36 mutation and also caused UV-induced mutation in the E. coli strain. In H. influenzae, pMucAMucB caused a small but reproducible increase in survival after UV irradiation in wild-type cells and in a rec-1 mutant, but there was no increase in spontaneous mutation in the wild type or in the rec-1 mutant and no UV-induced mutation.     

Enhanced survival of gamma-irradiated Escherichia coli following pretreatment with dithiothreitol

Survival of three strains of Escherichia coli K12 was studied with respect to radiation protection by dithiothreitol (DTT). The three strains compared were AB2462 recA, AB2470 rec21 and their DNA repair-competent prototype, AB1157. The strains were incubated in 10 mmol dm-3 DTT for 60 min and allowed an expression period for SOS functions to appear which may have been induced by DTT. Following the expression period the DTT-incubated cells and incubated control cells were irradiated. When AB1157 cells were pretreated with chloramphenicol (200 micrograms cm-3) for a period of 30 min prior to addition of the induction media no increase in survival was seen. When catalase (0.1 mg cm-3) was added to the AB1157 cells prior to the induction media a decrease in the degree of induction was noted with an enhancement ratio (ER) of 0.893 (ER-1 = 1.12). Furthermore, DTT-treated AB2462 and AB2470 demonstrated no increase in survival when compared to control cells. In radiation experiments on either strain of E. coli with or without DTT present during irradiation, the following were observed: (1) survival of AB1157 was enhanced with a dose modification factor (DMF) of 1.7 with DTT present and 1.3 with pretreatment; (2) the rec mutants showed no change in survival at any dose with a DMF of approximately 1.0. Results indicate that, using our protocol, inducible repair is of more importance than free radical scavenging by DTT. Furthermore, DTT-treated AB2462 demonstrated no increase in survival when compared to control cells. In radiation experiments on either strain of E. coli with and without DTT present during irradiation, the following were observed: (1) survival of AB1157 was enhanced with a DMF of 1.7 with DTT present during irradiation and 1.3 with only pretreatment; (2) the recA and recB mutants showed no change in cell survival at any dose with a DMF of approximately 1.0. Results indicate that, using our pretreatment protocol, inducible repair is of more importance in protection than free radical scavenging by DTT.     

Reduced restriction of phage lambda in Escherichia coli K-12 cells after gamma-irradiation

In gamma-irradiated cells of Escherichia coli K-12 restriction alleviation of an unmodified phage lambda is only observed in AB1157 strain. No restriction alleviation by gamma-rays is registered in AB1157 mutants (rec A and ssb-1).     

Characterization of the E.coli K12 strain AB1157 as impaired in guanine/xanthine metabolism

The widely used E. coli K12 strain AB1157 is impaired in guanine (xanthine) metabolism. Mutants blocked in purine biosynthesis before the stage of inosine monophosphate synthesis do not grow on external guanine or xanthine.The genetic nature of the Gua/Xan lesion is a deletion in the chromosome that covers the pro A gene. The lesion causes reduced uptake of guanine.     

Some group N plasmids makeEscherichia coli K-12 strain AB1157 dependent on exogenous purine

Escherichia coli K-12 strain AB1157 given the conjugative group N plasmid R46 (or its derivative, pKM101, or plasmid R384N) grew only very slowly on defined medium containing the known growth-factor requirements of AB1157, which do not include any purine. Addition of adenine or hypoxanthine (or their nucleosides) restored normal growth; guanine and xanthine (and their nucleosides) were ineffective, because of thegpt defect caused by deletionproA2. Variants of AB1157(R46) able to grow rapidly on defined medium without purine were tetracycline-sensitive and/or transfer-defective; an, R46 gene,slo, causing purine auxotrophy, is inferred to be betweentet andtra.     

Isolation and prevalidation of an Escherichia coli tester strain for the use in mechanistic and metabolic studies of genotoxins

We have isolated an Escherichia coli tester strain for the use in mechanistic and metabolic studies of genotoxins. We started with one of the more used and better characterized E. coli K-12 laboratory strains, AB1157. We isolated a lipopolysaccharide defective mutant of strain AB1886 which is an excision repair deficient derivative of AB1157 and introduced a newly constructed plasmid pKR11, encoding mucAB, resulting in strain MR2101/pKR11. A genotoxicity assay was designed, monitoring the reversion to arginine prototrophy and a preliminary validation was carried out against Ames tester strain TA100 with a set of diagnostic compounds. The results seem to indicate that strain MR2101/pKR11 is an adequate tester strain which can be a useful tool in mechanistic studies. Moreover, this strain can serve as mother strain to isolate improved and more especialized tester strains.     

Resonance effect of millimeter waves in the power range from 10-19 to 3 × 10-3 W/cm2 on Escherichia coli cells at different concentrations

The effect of millimeter waves (MMWs) on the genome conformational state (GCS) of E. coli AB1157 cells was studied by the method of anomalous viscosity time dependencies (AVTD) in the frequency range of 51.64-51.85 GHz. The 51.755 GHz resonance frequency of the cell reaction to MMWs did not depend on power density (PD) in the range from 10^-19 to 3 × 10^-3 W/cm². The half-width of the resonant reaction of cells showed a sigmoid dependence on PD, changing from 3 MHz to 100 MHz. The PD dependence of the half-width had the same shape for different concentrations of exposed cells (4 × 10⁷ and 4 × 10⁸ cells/ml), whereas the magnitude of the 51.755 GHz resonance effect differed significantly and depended on the PD of MMW exposure. Sharp narrowing of the 51.755 GHz resonance in the PD range from 10^-4 to 10^-7 W/cm² was followed by an emergence of new resonance frequencies. The PD dependence of the MMW effect at one of these resonance frequencies (51.674 GHz) differed markedly from the corresponding dependence at the 51.755 GHz resonance, the power window occurring in the range from 10^-16 to 10^-8 W/cm². The results obtained were explained in the framework of a model of electron-conformational interactions. The frequency-time parameters of this model appeared to be in good agreement with experimental data. © 1996 Wiley-Liss, Inc.     

meoA is the structural gene for outer membrane protein c of Escherichia coli K12

Summary The isolation and characterization of two mutants of Escherichia coli K12 with an altered outer membrane protein c is described. The first mutant, strain CE1151, was isolated as a bacteriophage Mel resistant strain which contains normal levels of protein c. Mutant cells adsorbed the phage with a strongly decreased rate. Complexes of purified nonheat modified wild type protein c and wild type lipopolysaccharide inactivated phage Me1, indicating that these components are required for receptor activity for phage Me1. When wild type protein c was replaced by protein c of strain CE1151, the receptorcomplex was far less active, showing that protein c of strain CE1151 is altered. The second mutant produces a protein c with a decreased electrophoretic mobility, designated as protein c^*. An altered apparent molecular weight was also observed for one or more fragments obtained after fragmentation of the mutant protein with cyanogen bromide, trypsin and chymotrypsin. Alteration of protein c was not accompanied by a detectable alteration in protein b or its fragments. Both mutations are located at minute 48 of the Escherichia coli K12 linkage map. The results strongly suggest that meoA is the structural gene for protein c.     

Isolation and characterization of a new globomycin-resistant dnaE mutant of Escherichia coli.

We isolated a globomycin-resistant, temperature-sensitive mutant of Escherichia coli K-12 strain AB1157. The mutation mapped in dnaE, the structural gene for the alpha-subunit of DNA polymerase III. The in vivo processing of lipid-modified prolipoprotein was more resistant to globomycin in the mutant strain 307 than in its parent. The prolipoprotein signal peptidase activity was also increased twofold in the mutant, and there was a threefold increase in the activity of isoleucyl-tRNA synthetase. The results suggest that a mutation in dnaE may affect the expression of the ileS-lsp operon in E. coli. In addition, strain 307 showed a reduced level of streptomycin resistance compared with its parental strain AB1157 (rpsL31). Strain 307 was killed by streptomycin at a concentration of 200 micrograms/ml, which did not affect the rate of bulk protein synthesis in this mutant. A second mutation which was involved in the reduced streptomycin resistance in strain 307 was identified and found to be closely linked to or within the rpsD (ramA, ribosomal ambiguity) gene. Both dnaE and rpsD were required for the reduced streptomycin resistance in strain 307.     

Applied AC and DC magnetic fields cause alterations in the mitotic cycle of early sea urchin embryos

This study demonstrates that exposure to 60 Hz magnetic fields (3.4–8.8 mT) and magnetic fields over the range DC-600 kHz (2.5–6.5 mT) can alter the early embryonic development of sea urchin embryos by inducing alterations in the timing of the cell cycle. Batches of fertilized eggs were exposed to the fields produced by a coil system. Samples of the continuous cultures were taken and scored for cell division. The times of both the first and second cell divisions were advanced by ELF AC fields and by static fields. The magnitude of the 60 Hz effect appears proportional to the field strength over the range tested. The relationship to field frequency was nonlinear and complex. For certain frequencies above the ELF range, the exposure resulted in a delay of the onset of mitosis. The advance of mitosis was also dependent on the duration of exposure and on the timing of exposure relative to fertilization. © 1995 Wiley-Liss, Inc.