Involvement of cyclic AMP and its receptor protein in filamentation of an Escherichia coli fic mutant

Cyclic AMP (cAMP) inhibited septum formation in Escherichia coli PA3092 and induced cell filamentation at elevated temperatures. This phenomenon was first observed in E. coli PA3092 and is due to a temperature-sensitive mutation. We tentatively named this mutation fic (filamentation induced by cAMP). The fic gene was located near rpsL (formerly strA) on the E. coli K-12 map. the inhibitory effect of cAMP on cell division and filamentation in a fic mutant was not observed in a crp mutant. When cAMP was removed from the culture medium, filaments were divided into rods as the intracellular cAMP level decreased. These results suggest that the cAMP-cAMP receptor protein complex causes filamentation in the fic mutant, E. coli PA3092.     

Functioning of the lactose operon of E. coli K-12 under the influence of non-specific regulators]

A possible role played by cAMP in the stimulating action of ACTH and hydrocortisone on lactose E. coli K-12 operon was studied. It was shown that ACTH caused no effect in the E. coli WZ-78/F'lac (cya855) and E. coli CA8001 (L1) strains with destroyed positive cAMP control system of the lactose operon function, at the same time producing a stimulating effect on the lactose operon in the strains of wild type, i.e. E coli 200PS/F'lac and E. coli 3000. Hydrocortisone stimulated the lactose operon function both in E. coli 3000 and in the mutant E. coli CA8001 (L1). It was supposed that the accelerating effect of ACTH on the lactose operon was mediated through cAMP; as to hydrocortisone--it stimulated the lactose operon function independently of cAMP.     

Influence of ionizing radiation of low intensity on the processes of reproduction,aging and dying off of Escherichia coli bacteria

The influence of 60Co gamma-ray irradiation of low intensity (0.1-0.4, 0.76 x 10(3) microGy/h) on the processes of reproduction, aging and dying off of E. coli B/r and E. coli BS-1 bacteria have been investigated. It was shown that the reproduction of this bacteria strains was not dependent on the dose rate in the range 0.1-0.4 microGy/h. It was shown in comparison with the irradiated E. coli B/r cells dynamics of the aging and dying off of the irradiated E. coli BS-1 is decreased in the process of prolonged (about 190 days) irradiation with a dose rate of 0.76 x 10(3) microGy/h. It is proposed the relationship between the revealed phenomenon of the decrease in the intensity of the irradiated E. coli BS-1 cell aging and dying and the Vavilov-Cerenkov emission.     

Elimination of Escherichia coli O157:H7 in meats by gamma irradiation.

Undercooked and raw meat has been linked to outbreaks of hemorrhagic diarrhea due to the presence of Escherichia coli O157:H7; therefore, treatment with ionizing radiation was investigated as a potential method for the elimination of this organism. Response-surface methods were used to study the effects of irradiation dose (0 to 2.0 kGy), temperature (-20 to +20 degrees C), and atmosphere (air and vacuum) on E. coli O157:H7 in mechanically deboned chicken meat. Differences in irradiation dose and temperature significantly affected the results. Ninety percent of the viable E. coli in chicken meat was eliminated by doses of 0.27 kGy at +5 degrees C and 0.42 kGy at -5 degrees C. Small, but significant, differences in radiation resistance by E. coli were found when finely ground lean beef rather than chicken was the substrate. Unlike nonirradiated samples, no measurable verotoxin was found in finely ground lean beef which had been inoculated with 10(4.8) CFU of E. coli O157:H7 per g, irradiated at a minimum dose of 1.5 kGy, and temperature abused at 35 degrees C for 20 h. Irradiation is an effective method to control this food-borne pathogen.     

Regulation of beta-galactosidase synthesis in Escherichia coli by exogenous cyclic 3',5'-adenosine monophosphate]

The effect of cyclic 3',5'-adenosine monophosphate (cAMP) on the rate of beta-galactosidase biosynthesis was studied in the cells of Escherichia coli M-17 growing in MPB and mineral media with glucose and maltose, i.e. under the conditions of various catabolite repression, as well as upon lac-operon induction by isopropyl-beta-D-galactopyranoside (IPGP). The stimulating action of exogenous cAMP was found only in a medium with salts and glucose. The induction by IPGP was highest during the growth in a medium with glucose and maltose. When the medium contained IPGP, cAMP accelerated the enzyme synthesis in all media, but only at the early growth phases, while cAMP eliminated the effect of IPGP at the stationary phase of growth. The regulation of beta-galactosidase biosynthesis by cAMP demonstrated for the first time that this effect depended on the physiological state of E. coli: the expression of catabolite-sensitive E. coli genes was subject to both positive and negative regulation in one and the same inducible system. The effect exerted by cAMP depended on the nature of a carbon source in the growth medium.     

Inhibitory effect of adenosine 3'',5''-phosphate on cell division of Escherichia coli K-12 mutant derivatives

Cell division of Escherichia coli K-12 strain PA3092 was inhibited by the addition of adenosine 3',5'-phosphate (cAMP), and the cellular morphology was changed from rods into filaments. Nucleoids in the filaments were regularly distributed and septum formation was perfectly inhibited. This inhibition of cell division by cAMP was reversed by the addition of guanosine 3',5'-monophosphate. To examine whether the inhibitory effect of cAMP on cell division in E. coli PA3092 was specific, its effect in several parental strains was investigated. Induction of cell filamentation by cAMP was observed in E. coli PA309 and P678, but not in E. coli W505, W1, Y10, or the wild-type strain. This result suggests that filamentation by cAMP in E. coli PA3092, PA309, and P678 was due to the mutagenesis by which E. coli P678 was derived from E. coli W595.     

环化腺苷酸对细菌生长的影响

用大肠杆菌(Escherichia coli AS 1.797)、北京棒状杆菌(Corynebacterium pekinense AS1.299)和巨大芽孢杆菌(Bacills megatertum AS 1.217)研究了细胞内环化腺苷酸(cAMP)浓度和外源cAMP对细胞生长的影响。结果表明,大肠杆菌在不同碳源中生长时,细胞的生长量随细胞内cAMF’浓度升高而降低。在以葡萄糖作碳源时,细胞内cAMP浓度低,外源cAMP。对生长有抑制作用,而cAMP的类似物5'-AMP则无抑制作用。在以乳糖、麦芽糖和甘油分别作碳源时,细胞内cAMP浓度高,外源cAMP对生长无影响。北京捧状杆菌以葡萄糖作碳源时,细胞生长也受外源cAMP的抑制,但cAMP的抑制作用不是专一的,它的作用可用类似物5’-AMP来代替。自身不合cAMP的巨大芽孢杆菌在不同碳原(包括葡萄糖)中生长时,生长不受外源cAMP抑制,也不受5’-Amt’的影响。因此认为,cAMP不是细菌生长的必需物,而是生长调节物,但这种调节物对巨大芽孢杆菌无效。     

Cell-density dependent effects of low-dose ionizing radiation on E. coli cells

The changes in genome conformational state (GCS) induced by low-dose ionizing radiation in E. coli cells were measured by the method of anomalous viscosity time dependence (AVTD) in cellular lysates. Effects of X-rays at doses 0.1 cGy--1 Gy depended on post-irradiation time. Significant relaxation of DNA loops followed by a decrease in AVTD. The time of maximum relaxation was between 5-80 min depending on the dose of irradiation. U-shaped dose response was observed with increase of AVTD in the range of 0.1-4 Gy and decrease in AVTD at higher doses. No such increase in AVTD was seen upon irradiation of cells at the beginning of cell lysis while the AVTD decrease was the same. Significant differences in the effects of X-rays and gamma-rays at the same doses were observed suggesting a strong dependence of low-dose effects on LET. Effects of 0.01 cGy gamma-rays were studied at different cell densities during irradiation. We show that the radiation-induced changes in GCS lasted longer at higher cell density as compared to lower cell density. Only small amount of cells were hit at this dose and the data suggest cell-to-cell communication in response to low-dose ionizing radiation. This prolonged effect was also observed when cells were irradiated at high cell density and diluted to low cell density immediately after irradiation. These data suggest that cell-to-cell communication occur during irradiation or within 3 min post-irradiation. The cell-density dependent response to low-dose ionizing radiation was compared with previously reported data on exposure of E. coli cells to electromagnetic fields of extremely low frequency and extremely high frequency (millimeter waves). The body of our data show that cells can communicate in response to electromagnetic fields and ionizing radiation, presumably by reemission of secondary photons in infrared-submillimeter frequency range.     

Functional properties of Borrelia burgdorferi recA

Functions of the Borrelia burgdorferi RecA protein were investigated in Escherichia coli recA null mutants. Complementation with B. burgdorferi recA increased survival of E. coli recA mutants by 3 orders of magnitude at a UV dose of 2,000 microJ/cm(2). The viability at this UV dose was about 10% that provided by the homologous recA gene. Expression of B. burgdorferi recA resulted in survival of E. coli at levels of mitomycin C that were lethal to noncomplemented hosts. B. burgdorferi RecA was as effective as E. coli RecA in mediating homologous recombination in E. coli. Furthermore, E. coli lambda phage lysogens complemented with B. burgdorferi recA produced phage even in the absence of UV irradiation. The level of phage induction was 55-fold higher than the level in cells complemented with the homologous recA gene, suggesting that B. burgdorferi RecA may possess an enhanced coprotease activity. This study indicates that B. burgdorferi RecA mediates the same functions in E. coli as the homologous E. coli protein mediates. However, the rapid loss of viability and the absence of induction in recA expression after UV irradiation in B. burgdorferi suggest that recA is not involved in the repair of UV-induced damage in B. burgdorferi. The primary role of RecA in B. burgdorferi is likely to be a role in some aspect of recombination.     

Requirement of Cyclic Adenosine 3′,5′-Monophosphate for the Thermosensitive Effects of Rts1 in a Cyclic Adenosine 3′,5′-Monophosphate-Less Mutant of Escherichia coli

Previous publications showed that a covalently closed circular (CCC) Rts1 plasmid deoxyribonucleic acid (DNA) that confers kanamycin resistance upon the host bacteria inhibits host growth at 42 degrees C but not at 32 degrees C. At 42 degrees C, the CCC Rts1 DNA is not formed, and cells without plasmids emerge. To investigate the possible role of cyclic adenosine 3',5'-monophosphate (cAMP) in the action of Rts1 on host bacteria, Rts1 was placed in an Escherichia coli mutant (CA7902) that lacks adenylate cyclase or in E. coli PP47 (a mutant lacking cAMP receptor protein). Rts1 did not exert the thermosensitive effect on these cells, and CCC Rts1 DNA was formed even at 42 degrees C. Upon addition of cAMP to E. coli CA7902(Rts1), cell growth and formation of CCC Rts1 DNA were inhibited at 42 degrees C. The addition of cAMP to E. coli PP47(Rts1) did not cause inhibitory effects on either cell growth or CCC Rts1 DNA formation at 42 degrees C. The inhibitory effect of cAMP on E. coli CA7902(Rts1) is specific to this cyclic nucleotide, and other cyclic nucleotides such as cyclic guanosine 3',5'-monophosphate did not have the effect. For this inhibitory effect, cells have to be preincubated with cAMP; the presence of cAMP at the time of CCC Rts1 DNA formation is not enough for the inhibitory effect. If the cells are preincubated with cAMP, one can remove cAMP during the [(3)H]thymidine pulse and still observe its inhibitory effect on the formation of CCC Rts1 DNA. The presence of chloramphenicol during this preincubation period abolished the inhibitory effect of cAMP. These observations suggest that cAMP is necessary to induce synthesis of a protein that inhibits CCC Rts1 DNA formation and cell growth at 42 degrees C.     

Elaboration of chloramphenicol acetyltransferase by cells of E. coli K-12 under conditions altering the intracellular concentration of cyclic adenosine-3',5'-monophosphate]

The influence of cAMP, ACTH and glucose on the stimulation of chloramphenicol acetyl transferase synthesis in the cells of E. coli CSH-2/R222 and E. coli WZ-78/R222. (cya855) was examined. Glucose proved to decrease the enzyme synthesis in E. coli CSH-2/R222, causing catabolite repression; 5 mM of cAMP and 1000 mug/ml ACTH overcame the latter. The enzyme synthesis in E. coli WZ-78/R222 was insensitive to the catabolite repression; as to ACTH - it failed to cause stimulation ofchloramphenicol acetyl transferase synthesis in E. coli WZ-78/R222.     

Suppression of induced beta-galactosidase synthesis by cysteamine and its reversion by gamma-irradiation in the presence of ascorbate.

The induced synthesis of beta-galactosidase in E. coli was found to be inhibited by cysteamine. This inhibitory effect of the SH compound was antagonized by the addition of ascorbate followed by gamma-irradiation with relatively low doses. The cAMP level which, it has been suggested, plays a role in the radioprotective action of cysteamine, is stabilized by ascorbate against changes induced by irradiation.     

The effect of low-intensity light from the red and far red regions of the spectrum on Escherichia coli

The effect of red and far red light having a low intensity on Escherichia coli growth was studied. The growth accelerated when the culture was irradiated with the light at a dose of 1--4 X 10(3) J/m2. When the light of the two spectral regions was used together, the effect depended on the dose and order of the irradiation. It is possible that receptors for red light and for far red light interact in E. coli cells.     

Effect of gamma-irradiation of Escherichia coli on cyclic AMP binding activity

Cyclic AMP binding in the extract of E. coli was taken as a measure of cAMP receptor protein (CRP) present in the cells. The gamma-irradiation of cells caused a dose-dependent inhibition of cAMP binding activity indicating that CRP gene is affected by gamma-irradiation. The binding activity in cells irradiated with 240 Gy gamma-ray dose remained unaltered by post-irradiation incubation. This supports previous finding that the enhanced inhibition of the L-arabinose isomerase synthesizing capacity, following incubation of gamma-irradiated cells at higher doses, must be due to a different cause than the catabolite repression.     

Radiation sensitivity of <Emphasis Type="Italic">N. pharaonis</Emphasis> in comparison with <Emphasis Type="Italic">E. coli </Emphasis>K12 strains

To investigate the radiation sensitivity of the natronobacterium Natronomonas pharaonis in comparison with Escherichia coli strains (N. pharaonis DSM 2160T, E. coli strains AB1157 and K12 lambda s) were exposed to gamma-radiation (60Co-gamma-source, 100 Gy min-1) in the presence of oxygen (air) and under strongly reduced oxygen conditions (argon-saturated medium). After irradiation, the colony-forming ability (dose-survival curves) and the D37 dose were determined. The oxygen content of the solutions containing high NaCl concentrations was measured with an oxygen electrode (Clark electrode). It was found that N. pharaonis can tolerate a remarkably higher irradiation dose than the two E. coli strains (approx. 1.5-fold of K12 lambda s and approx. 4-fold of AB1157). The oxygen enhancement ratio (OER) is 2.8 for N. pharaonis and 2.6 for both E. coli strains. Therefore the higher radiation resistance of the N. pharaonis is not due to the low oxygen content of the cell solution (high salt concentration) but is probably related to the higher DNA repair ability of this archaebacteria strain.     

Construction of an Escherichia coli strain which excretes abnormally large amounts of adenosine 3',5'-cyclic monophosphate.

It has previously been shown that an Escherichia coli CRP- strain 5333 accumulates abnormally large amounts of adenosine 3',5'-cyclic monophosphate (cAMP). Using P1 transduction, the CRP- character was transferred to E. coli Crookes strain which is deficient for cAMP phophodiesterase (CPD-). The resulting strain HY22 (CRP-, CPD-) accumulates greater amounts of cAMP both intracellularly and extracellularly than does 5333. In glucose minimal medium, an HY22 cell accumulates 100 times more cAMP intracellularly and excretes cAMP 150 times faster than does a wild-type E. coli cell.     

光复活对紫外线照射大肠杆菌后突变率的影响

通过改变UV照射时间、照射后的操作速度、光复活时的温度、时间和光强度,以光复活和暗处理后细胞存活数的比值为依据,研究了不同条件下E．coli受UV照射后的光复活效应。并以E．coli对5μg/ml链霉素抗性突变率为指标,比较了不同剂量UV照射后光复活和暗处理对E．coli突变率的影响。结果表明：光复活效应在温度10℃时最明显,且与照射时间、照射后的操作速度、光复活时间和光强度成正相关;在中、低剂量UV照射后,暗处理较光复活后E．coli对链霉素抗性突变率明显高,而在高剂量下,光复活则显著高于暗处理后的突变率。