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Introduction. Currently, the search for new antibacterial substances is an urgent task due to the growing resistance of pathogens to existing antibiotics. One of the key directions in this area is the expansion of scientific research of medicinal plants, as new sources of therapeutic agents. This article examines the possibility of using highly sensitive bioluminescent test bacteria for these purposes, which can quickly detect non-specific antimicrobial activity and can be adapted to highly effective pharmaceutical screening technologies.Aim. To study the applicability of bioluminescent bacteria for the analysis of the antibacterial activity of biologically active substances (BAS) of plant origin.Materials and methods. BAS quercetin, 8-hydroxyquinoline, gallic acid and thymoquinone, which are often found in medicinal plant raw materials and with which its antibacterial properties are associated, were used in the work. Bacteria with constitutive bioluminescence Aliivibrio fischeri F1 and Escherichia coli (pXen7), as well as recombinant bioreporter strains with inducible luminescence were used as test-objects: E. coli (pRecA-lux), E. coli (pColD-lux), reacting to nucleic acid damage; E. coli (pKatG-lux) and E. coli (pSoxS-lux), sensitive to oxidative stress.Results and discussion. It was found that the nonspecific antimicrobial activity of the studied BAS is manifested in the inhibition of bacterial bioluminescence of test-strains with constitutive glowing. It was noted that the marine test-bacteria A. fischeri F1 have significantly greater sensitivity to the action of BAS, compared with the recombinant strain of E. coli (pXen7). It has been shown that their inhibitory effect begins at concentrations of 2 mcg/ml, and bactericidal activity occurs at concentrations of more than 20 mcg/ml. The results obtained are compared with the data on MIC and MBC of gram(+) and gram(–) pathogens. The study of the induction of bioluminescence of recombinant bioreporter strains showed that the antibacterial effect of the BAS is accompanied by oxidative stress. Also, quercetin caused activation of luminescence in E. coli (pRecA-lux) and E. coli (pColD-lux), which may indicate its participation in damage to nucleic acids. Analysis of the induction factors of bioreporter strains indicates that the revealed mechanisms of antibacterial activity are not major, but may be of a secondary nature.Conclusion. It has been shown that the intensity of the glow of natural and recombinant bioluminescent bacteria can be an indicator of the antibacterial activity of BAS of natural origin. The high sensitivity of A. fischeri F1 bacteria to the action of substances such as quercetin, 8-hydroxyquinoline, gallic acid and thymoquinone has been shown. Considering that bioluminescence analysis is a quantitative instrumental method, it can be easily adapted for high-throughput pharmaceutical screening. It has been shown that the luminescence intensity of natural and recombinant bioluminescent bacteria can be an indicator of the antibacterial activity of BAS of natural origin. The high sensitivity of A. fischeri F1 to the action of substances such as quercetin, 8-hydroxyquinoline, gallic acid and thymoquinone has been established. Taking in an account that bioluminescent analysis is a quantitative instrumental method, it can be easily adapted for high-throughput pharmaceutical screening.

The light emitted by a luminescent bacterium serves as a unique native channel of information regarding the intracellular processes within the individual cell. In the presence of highly sensitive equipment, it is possible to obtain the distribution of bacterial culture cells by the intensity of light emission, which correlates with the amount of luciferase in the cells. When growing on rich media, the luminescence intensity of individual cells of brightly luminous strains of the luminescent bacteria Photobacterium leiognathi and Ph. phosporeum reaches 104–105 quanta/s. The signal of such intensity can be registered using sensitive photometric equipment. All experiments were carried out with bacterial clones (genetically homogeneous populations). A typical dynamics of luminous bacterial cells distributions with respect to intensity of light emission at various stages of batch culture growth in a liquid medium was obtained. To describe experimental distributions, a phenomenological model that links the light of a bacterial cell with the history of events at the molecular level was constructed. The proposed phenomenological model with a minimum number of fitting parameters (1.5) provides a satisfactory description of the complex process of formation of cell distributions by luminescence intensity at different stages of bacterial culture growth. This may be an indication that the structure of the model describes some essential processes of the real system. Since in the process of division all cells go through the stage of release of all regulatory molecules from the DNA molecule, the resulting distributions can be attributed not only to luciferase, but also to other proteins of constitutive (and not only) synthesis.

At the beginning of the paper, the level of necessary phenomenology of complex models is discussed. When working with complex systems, which of course include living organisms and ecological systems, it is necessary to use a phenomenological description. An illustration of the phenomenological approach is given, which captures the most significant general principles or patterns of interactions; the specific values of the parameters cannot be calculated from the first principles, but are determined empirically. An appropriate interpretation is also chosen empirically and pragmatically. However, in order to simulate a wider range of situations, it becomes necessary to lower the level of phenomenology, switch to a more detailed description of the system, introducing interaction between selected elements of the system. The requirements for a system model combining ecological, metabolic and genetic levels of cell culture description are formulated. A mathematical model of quorum sensing dynamics during the growth of batch culture of luminescent bacteria at different concentrations of the nutrient substrate has been developed. The model contains four blocks describing ecological, energy, quorum and luminescent aspects of bacterial culture growth. The model demonstrated good agreement with the experimental data obtained. When analyzing the model, three oddities in the behavior of the culture were noted, which presumably can change the idea of some processes taking place during the development of a culture of luminescent bacteria. The results obtained suggest the presence of some additional control system for the luminescent reaction via the synthesis pathways of FMN · Н2 or aliphatic aldehyde. In this case, the generalized description of the contribution of energy metabolism to luminescence only through ATP is too strong a simplification. As a result of comparing the model dynamics with the experiment, a discrepancy arose between the concentration of the substrate (peptone) measured in the experiment and its effective influence on the bacterial population growth. This discrepancy seems to indicate peptone is not the leading substrate, and growth is limited by nutrients contained in the yeast extract, the concentration of which did not change in these experiments. The discrepancies noted between the expectations and the results of experimental data processing, together with the assumptions about the causes of these discrepancies, set the direction for further experimental and theoretical studies of quorum sensing mechanisms in a culture of luminescent bacteria.