[Topological changes in DNA as a reflection of adaptation of Escherichia coli to oxidative stress under glucose starvation and transition to growth]. / Topologicheskie izmeneniia DNK kak otrazhenie adaptatsii Escherichia coli k okislitel'nomu stressu v usloviiakh golodaniia po gliukoze i pri perekhode k rostu.

Changes in the topological state of DNA occur in a starving Escherichia coli culture under oxidative stress caused by the addition of hydrogen peroxide. The addition of a carbon and energy source to this culture results in a second stress reaction. This supports previous data indicating that different mechanisms are responsible for the cell defense against oxidative stress in exponential and starving E. coli cultures. Polyamine synthesis is involved in the cell adaptation to the stress. Putrescine binding to DNA and its dissociation seem to modulate the DNA topological state, which regulates the expression of the adaptive genes. An increase in the activity of the polyamine-synthesizing system in response to oxidative stress leads to a putrescine flux across the cytoplasmic membrane, due to which the antioxidant activity of putrescine protects the membrane phospholipids and contributes to the restoration of the cell energy-generating function.

[Phasic changes in reproductive potential, intracellular polyamines and antilysozyme activity in Escherichia coli in periodic culture]. / Fazovye izmeneniia reproduktivnogo potentsiala, vnutrikletochnykh poliaminov i antilizotsimnoi aktivnosti u Escherichia coli v periodicheskoi kul'ture.

Growth-phase associated changes in and relationships between the specific growth rate (mu) characterizing the reproductive capacity of the cells, the contents of intracellular biogenic polyamines (BPA), such as putrescine (P), cadaverine (C), and spermidine (S), and antilysozyme activity (ALA) were studied in 37 strains of Escherichia coli grown in batch culture on solid medium. A decrease in mu upon the transition of the culture to the stationary growth phase was accompanied by a decrease in the pool of free BPA, mainly P and C, and by the appearance of ALA. The interrelations between the parameters studied were described as a complex of direct and negative correlations; the combination of low initial P and C contents, reduced P/S and C/S ratios, and a high level of ALA was designated as a factor of slight inhibition of E. coli reproduction. It is argued that BPA and ALA are integrated in a system controlling both the metabolism and stability of peptidoglycan in E. coli.

[The role of putrescine and the energy state of Escherichia coli in regulation of DNA topology during adaptation to oxidative stress]. / Rol' putresysina i énergeticheskogo sostoianiia Escherichia coli v re guliatsii topologii DNK pri adaptatsii k okislitel'nomu stressu.

An exponential-phase culture of E. coli responded to the addition of H2O2 by a decrease in DNA supercoiling induced by the lowering of the energy status of cells, potassium leakage, and breaking of polynucleotide chains. Extending the time of exposure of E. coli cells to hydrogen peroxide led to an increase in the intracellular pools of putrescine and potassium, promotion of cellular energy status, and the restoration of DNA supercoiling to values much in excess of the prestress level. The subsequent stabilization of the intracellular putrescine pool was accompanied by a release of this polyamine from the cell. Based on these results and those available in the literature, a mechanism of E. coli adaptation to oxidative stress is suggested that assigns roles to putrescine, potassium, and cellular energy status.

[Role of putrescine and potassium transport in regulating the topological state of DNA during adaptation of Escherichia coli to temperature stress]. / Rol' transporta putrestsina i kaliia v reguliatsii topologicheskogo sostoianiia aDNK v protsesse adaptatsii Escherichia coli k temperaturnomu stressu.

The effect of a temperature increase to 52 degrees C or the addition of ethanol (6%) to an exponential Escherichia coli culture on putrescine and potassium transport was studied. The first stage of heat shock was accompanied by a decrease in the extent of DNA supercoiling, due to the dissociation of the putrescine-DNA complex. The loss of potassium ions at this phase produced a synergistic effect. The second phase of the heat shock was characterized by a reversal in the direction of putrescine and potassium transport, which was accompanied by restoration of the prestress extent of DNA supercoiling. An increase in the ATP pool and cell energy charge resulting from the uncoupling of the energy metabolism and synthetic processes also played an important role in the restoration of the DNA initial topology at the second phase of the heat shock via the activation of the energy-dependent gyrase or the heat shock protein DnaK. A mechanism is suggested that explains the involvement of putrescine in the regulation of DNA topology, which is a universal regulator of gene expression under stress, heat shock in particular.

[Exchange of putrescine and potassium between cells and media as a factor in the adaptation of Escherichia coli to hyperosmotic shock]. / Obmen putrestsina i kaliia mezhdu kletkoi i sredoi kak faktor adaptatsii Escherichia coli k giperosmoticheskomu shoku.

Putrescine/potassium exchange in response to hyperosmotic stress was studied. The addition of 0.3 M NaCl or 0.44 M sucrose to an exponentially growing E. coli culture induced potassium uptake and putrescine release from the cell. Potassium added to an osmotically stressed potassium-deficient culture was readily absorbed by cells; this was accompanied by the loss of intracellular putrescine, both free and bound. Since DNA is the main binding site of putrescine, the loss of bound putrescine caused a relaxation of DNA supercoiling. The increase in the intracellular content of potassium not only restored but also enhanced DNA supercoiling as compared to the initial level. In vitro experiments showed the degree of plasmid DNA supercoiling to rise drastically at potassium concentrations of 300-500 mM, while different putrescine concentrations affected this parameter differently. Thus, the physiological concentrations of putrescine (below 1 mM) greatly augmented DNA supercoiling, whereas higher concentrations (5-10 mM) exerted a relaxing effect. A change in DNA supercoiling in vivo in response to osmotic stress is the result of competition between biogenic and abiogenic cations for the sites of binding to polyanionic DNA structures. A change in DNA topology serves as the regulatory factor controlling the expression of genes responsible for cell adaptation to osmotic stress.

[Role of putrescine and potassium transport in the adaptation of Escherichia coli to ammonium starvation]. / Rol' transporta putrestsina i kaliia v adaptatsii Escherichia coli k golodaniiu po ammoniiu.

Ammonium depletion in the nutrient medium induced an active transport of putrescine into the cell, which was not associated with its utilization as a nitrogen source. The uptake of putrescine was accompanied by a proportional release of potassium from the cells. Quantitative analysis of free as well as weakly and tightly bound pools of putrescine showed that this diamine was bound mainly to DNA. Topological studies by the plasmid method indicated an increase in the DNA supercoiling in response to the putrescine transport. In vitro experiments made it possible to establish an ambiguous dependence of DNA topology on putrescine content--its physiological concentrations (0.5-1.0 mM) enhanced DNA supercoiling, while higher concentrations (2-10 mM) caused gradual relaxation of DNA. A possible physiological significance of these effects in adaptive response of cells to ammonium deficiency is discussed.

[Distribution of polyamines in Escherichia coli and their role in potassium exchange between the cell and the environment during aerobiosis-anaerobiosis transitions]. / Raspredelenie poliaminov u Escherichia coli i ikh rol' v obmene kaliia mezhdu kletkoi i sredoi v protsesse aérobno-anaérobnykh perekhodov.

The transition of E. coli cells to anaerobiosis is accompanied by the onset of two cellular cation flows in different directions: potassium is released into the environment, and putrescine enters the cells. If aerobic conditions are reestablished, the cation flows change directions. Under anaerobiosis, the cell components bind putrescine. Investigation of the chemical interactions resulting in putrescine binding and metabolic conversion under anaerobic conditions revealed DNA to be the main target in this process. The driving forces and mechanisms of cation transfer are discussed, and the involvement of putrescine in topological changes in the DNA and the development of adaptive cell responses to anaerobiosis is considered.