Genetic control of Vibrio cholerae pathogenicity: the temperate filamentous phage CTX, coding for cholera toxin and the "island of pathogenicity"

Reviews modern data on the genetic control of the key factors of Vibrio cholerae pathogenicity: cholera toxin and toxin-coregulated adhesion pili. Pays special attention to the temperate filamentous CTX bacteriophage, whose genome contains structural genes of cholera toxin, and the "pathogenicity island" carrying tcp genes responsible for the most important factor of the human small intestine colonization with V. cholerae. Discusses the mechanism of coordinated regulation of the activity of the main genes of V. cholerae pathogenicity genes.     

The role of antioxidant systems in response of bacteria Escherichia coli to heat shock]

Shifting the temperature from 30 to 45 degrees C in an aerobic Escherichia coli culture inhibited the expression of the antioxidant genes katG, katE, sodA, and gor. The expression was evaluated by measuring beta-galactosidase activity in E. coli strains that contained fusions of the antioxidant gene promoters with the lacZ operon. Heat shock inhibited catalase and glutathione reductase, lowered the intracellular level of glutathione, and increased its extracellular level. It also suppressed the growth of mutants deficient in the katG-encoded catalase HPI, whereas the sensitivity of the wild-type and sodA sodB mutant cells to heat shock was almost the same. In the E. coli culture adapted to growth at 42 degrees C, the content of both intracellular and extracellular glutathione was two times higher than in the culture grown at 30 degrees C. The temperature-adapted cells grown aerobically at 42 degrees C showed an increased ability to express the fused katG-lacZ genes.     

Near-ultraviolet radiation and hydrogen peroxide modulate intracellular levels of potassium and thiols inEscherichia coli

Treatment of aerobicEscherichia coli K 12 with nonlethal doses of near-ultraviolet (NUV) and H₂O₂ resulted in the same physiological response. In response to stress caused by these agents, an inhibition of growth, a decrease in intracellular K⁺ pool, and an increase in intracellular levels of protein and nonprotein thiols were observed. A possible role for glutathione in the process of adaptation ofE. coli culture to growth under the conditions of oxidative stress is discussed.     

Kinetic models for the action of cytosolic and mitochondrial inorganic pyrophosphatases of rat liver

Initial rates of PPi hydrolysis by cytosolic and mitochondrial inorganic pyrophosphatases of rat liver have been measured in the presence of 0.2-100 microM MgPPi and 0.01-50 mM Mg2+ at pH 7.2 to 9.3. The apparently simplest model consistent with the data for both enzymes implies that they bind substrate, in the form of MgPPi, and three Mg2+ ions, of which two are absolutely required for activity. The third metal ion facilitates substrate binding but decreases maximal velocity for the cytosolic enzyme, while substrate binding is only modulated for the mitochondrial enzyme. The model is also applicable to bovine heart mitochondrial pyrophosphatases. The active form of the substrate for the cytosolic pyrophosphatase is MgP2O7(-2); the catalytic and metal-binding steps require a protonated group with pKa = 9.2 and an unprotonated group with pKa = 8.8, respectively. The results indicate that the mitochondrial pyrophosphatase is more sensitive to variations of Mg2+ concentration in rat liver cells than is the cytosolic one.     

Inheritance and expression of cholera toxin genes introduced into Vibrio cholerae el tor cells in a hybrid plasmid

Two replicons, pOX38 (in F-factor derivative lacking all IS elements) and pCT105 (containing cholera toxin operon cloned in pBR322) have been fused to produce recombinant plasmid, pCO109, which was then introduced into Vibrio cholerae eltor by conjugation. Restriction analysis showed pCO109 to dissociate in V. cholerae cells at a higher frequency than in Escherichia coli strains, its pOX38 component being lost, while the pCT105 component demonstrated relative stability. V. cholerae eltor RV79 (pCT105) produced 4-5 micrograms/ml of cholera toxin. Occasional insertion of cloned vctA, B operon into RV79 chromosome was also observed.     

A trial to decrease hepatitis A morbidity in Dzerzhinsk, Gorki Province

The results of experience in the comparative evaluation of the preseasonal immunoglobulin prophylaxis in two towns of the Gorki Province are presented. The work substantiates the economic and epidemiological effectiveness of immunoglobulin prophylaxis at the territory, relatively safe with respect to hepatitis A, under the conditions of its realization in the year of the predicted rise of morbidity, the timely organization of immunoglobulin prophylaxis (from July to the first half of October) and the coverage of "organized" children, exceeding 90%.     

Destructive and restorative processes of the liver in rats under intensive physical loading

The ultrastructure of rat liver cells after running exercise was investigated. When rats were trained for a month and sacrificed immediately after the last exercise it was revealed that the number of liver cells mitochondria increased, but many of them had alterations: mitochondria became swollen, had lucid matrix. There were some variations in degree of alterations between different mitochondria: a) in the same hepatocyte, b) in different hepatocytes of the same animal, that was connected with individual sensitivity of organelles on the levels of the cell and of the organ. Rough endoplasmic reticulum bore few ribosomes. Glycogen was absent. There were abundant vesicles of smooth endoplasmic reticulum, autophagic vacuoles and peroxisomes in the liver cell cytoplasm. Adaptation of rat liver to the exercise programme becomes evident by 1.5 month of exercise. Mitochondria and rough endoplasmic reticulum were numerous and of normal structure. There were many peroxisomes and glycogen granules in the cytoplasm of hepatocyte. The presence of large autophagic vacuoles in the cytoplasm of some hepatocytes were obviously connected with more rapid destruction of some organelles, than in control.     

The effect of inhibitors of ionic passive transport on the structure of a cell population of Ehrlich's ascites carcinoma

Triampur is a drug, containing triamterene and dichlotiazide, which inhibits passive influx of Na+ through cell membrane. Triampur was injected intraperitoneally to mice with the Ehrlich ascite carcinoma. The drug was injected in the exponential phase of tumor growth with 2 hour intervals within 24 hours. A subsequent sedimentation and fractionation of cells according to the cell cycle position displayed an additional peak in sedimentogram, that was absent in the control sedimentogram. This peak is due to cell blocking in G1-period; the pool of blocked cells contains 20-25% of the total cell population. If the drug was injected during 3 days and nights with 8-hour intervals, the pool of blocked cells amounted up to 40%. This effect is reversible: when the drug is cancelled, the peak of G1-blocked cells is reduced. Estimation of intracellular Na(+) and K(+) concentration and Na+, K(+) pump indicates a significant decrease in Na+ permeability in the blocked cells due to Triampur effect. The obtained data well compare with an idea of the importance of increasing a passive influx of Na+ for G1-S transition, and indicate a possibility to affect the structure of tumor cell population via the system of intracellular ionic homeostasis.