Elena Alexandrovna Timofeeva-Resovskaya at the forefront of radiobiology in the XX century.

PURPOSE: The purpose of the study was to show the outstanding contribution of Elena Alexandrovna Timofeeva-Resovskaya (1898-1973) to the development of radiobiology. MATERIALS AND METHODS: We reviewed the author's memoirs and materials from the personal archive, as well as literary and electronic sources. RESULTS AND CONCLUSIONS: For the first time the autobiography of Elena A. Timofeeva-Resovskaya and the periods of her scientific activity were revealed. We demonstrated the primary role of Elena A. Timofeeva-Resovskaya in the research of aquatic ecosystems. The results of her research turned out to be important both for solving the problems of radioactive contamination of territories and for the development of modern radioecology. Throughout her life, she worked with her husband Nikolay V. Timofeev-Resovsky (1900-1981), a great scientist and prominent scientific enlightener. There was no purpose to describe the life of Timofeev-Resovskies family, full of exciting events, but it was not possible to avoid it. For young women in science, Elena A. Timofeeva-Resovskaya can provide an example of a successful scientific career even in turbulent times.

[Determination of antibacterial activity of chitosan].

A method for the determination of the antimicrobial activity of chitosan with the use of organic salts for the production of pH in the range of 5.5-8.2 was studied. The double-dilution method demonstrated the effectiveness of the determination of the antimicrobial activity of chitosan samples with different molecular weights and solubilities. It was found that the antibacterial activity of chitosan samples with different molecular weights and solubilities. It was found that the antibacterial activity increased at low pH values with increasing molecular weight, but chitosan with a molecular weight of 5-6 kDa showed higher activity at neutral and slightly alkaline pH levels. Determination of the antimicrobial activity of various chitosan samples at different pH values allowed a more reliable assessment of the potential biological activity of chitosan.

[Comparative evaluation of antimicrobial activity of oligochitosans against Klebsiella pneumoniae].

Antibacterial activity of chitosan with different molecular weight at different pH values against gram-negative Klebsiella pneumoniae was studied. It was found that the dependence of inhibition activity of chitosan on its molecular weight was inversed when the medium pH was increased above 7.0. In acidic media higher molecular weight chitosan had the higher antibacterial activity was occured while and in weak alkaline media oligomeric forms of chitosan displayed the inhibition effect only. Our results showed that the antibacterial activity of chitosan against Klebsiella pneumoniae was closely connected with its polycationic nature, and was dependent on the degree of protonation of chitosan amino groups, which at the same time depended on the degree of polymerization and solution pH values.

[Influence of Polycations on Antibacterial Activity of Lysostaphin].

The synergistic antibacterial activity of lysostaphin and polycations of different chemical structures against Staphylococcus aureus has been shown. Polycations improved the lytic activity of lysostaphin against the peptidoglycan of staphylococci. It is proposed that this resulted in decreased binding of positively charged lysostaphin with S. aureus cell-wall teichoic acids. These data provide an opportunity to search for polycations that would amplify the synergistic effect of lysostaphin or other antibacterial proteins against staphylococci.

Effect of chitosan on lysostaphin lysis of staphylococcal cells.

The studied stimulation of lysostaphin-mediated lysis of staphylococcal cell walls under the effect of chitosan. The results suggested a mechanism of antibacterial activity of chitosan consisting in stimulation of bacterial cell wall degradation by its own autolysins in the presence of chitosan polymer.

[Antibacterial and antimycotic activity of chitosan: mechanisms of action and role of the structure].

Chitosan biopolymer obtained by deacetylation of chitin has antibacterial and antimycotic action. Known data about mechanisms of biocide effect of chitosan are described in the review. Role of chemical structure--molecular weight, level of deacetylation and presence of nanoparticles--in the expression of antibacterial and antimycotic activity is discussed.

[Obtaining and study of monosaccharide derivatives of low-molecular-weight chitosan].

The possibility of obtaining monosaccharide derivatives of low-molecular-weight chitosan with the use of the Maillard reaction was studied. Chitosan derivatives (molecular weight, 24 and 5 kDa) obtained with glucosamine, N-acetyl galactosamine, galactose, and mannose with a substitution degree of 4-14% and a yield of 60-80% were obtained. Some physicochemical and biological properties of these derivatives were studied. We showed that monosaccharide derivatives of low-molecular-weight chitosan exhibited antibacterial activity. Chitosan at a concentration of 0.01% caused 100% death of bacteria B. subtilis and E. coil. The strongest antibacterial effect was exhibited by 24-kDa derivatives: only 0.02-0.08% of cells survived. These derivatives were two orders of magnitude more effective than the 5-kDa chitosan modified with galactose.

[Effect of the molecular weight of chitosan on its antiviral activity in plants].

The effect of the molecular weight of chitosan on its ability to suppress systemic infection of bean mild mosaic virus in bean (Phasoleus vulgaris L.) plants was studied. The enzymatic hydrolysate of low-molecular-weight chitosan was successively fractionated by ultrafiltration through membranes with decreasing pore size. In total, four chitosan fractions with a weight-average molecular weight varying from 1.2 to 40.4 kDa were obtained. It was shown that the treatments of bean plants with these fractions (chitosan concentration, 10 or 100 microg/ml) inhibited virus accumulation and systemic propagation. The degree of chitosan-induced antiviral resistance increased as the molecular weight of chitosan decreased. The monomers comprising the chitosan molecule-glucosamine and N-acetylglucosamine--exhibited no antiviral activity.

[Biological preparations with different mechanism of action for protecting potato against fungal diseases].

Mycological analysis throughout the vegetation period of potato (Solanum tuberosum) made it possible to study in detail the structure of micromycete community, to determine typical dominant (frequency, more than 60%), typical common (frequency, 30 to 60%), typical rare (frequency, 10 to 30%), and casual (frequency, less than 10%) species and to estimate changes in the microorganism community caused by plant protection preparations with different mechanisms of action. It was shown that, as a result of occurrence of resistant forms, synthetic preparations against fungal pathogens of potato (such as TMTD, Ridomil gold MC, and Cupricol) were only slightly more effective than biological preparations (Trichodermin and AgroChit), with the former considerably changing the natural saprophytic mycological community. An increase in the soil pool of Trichoderma harzianum as a result of application of a biological preparation based on this antagonistic fungus correlated with its effectiveness against the soil pathogen Fusarium sp., which causes root rots. A chitosan-based elicitor preparation more effectively suppressed the development of early (Alternaria sp. and Macrosporium sp.) and late (Phytophthora sp.) blights of leaves and had a weaker effect on the soil microflora.