The problem of the prolonged and stable intensity of bioluminescent signals is relevant in the development of any test systems that use biological objects. The aim of this work was to study the features of bioluminescence dynamics of Photobacterium phosphoreum IMV B-7071 in a liquid and on different stationary media. Methods. Bioluminescence studies were performed in liquid, agarose, and cellulose-cotton media. Bacterial suspensions were cultivated at 21°C in the mediums with standard composition. We studied both the background glow and its dynamics under conditions of mixing a liquid medium. Bioluminescence was recorded using digital photography with subsequent image processing of the samples. The measurements of luminescence were made by digital photo or video recording using Olympus digital camera SP560UZ, CANON 700D, and mobile device camera Samsung Galaxy 9 Note with specialized applications for mobile devices "Colorimeter (Lab Tools Apps)" and Camera Color Counter (Keuwsoft) at maximum light sensitivity in the automatic white balance mode at a fixed distance from the sample. Image processing was carried out using ImageJ and Origin Pro. Spectra of bacterial luminescence and its dynamics over time were measured using an LOMO MDR-23 spectrometer in the range of 200–750 nm. Results. The results of the study prove that in aqueous or solid agar and also on cellulose cotton medium, the intensity of bioluminescence of P. phosphoreum gradually increases, reaching a maximum within approximately 2 days, after which it slowly fades. It was established that the bioluminescence of photobacterium P. phosphoreum is a non-stationary process and has characteristic features of temporal dynamics associated with both the dynamics of the oxygen concentration in the environment of bacterial suspensions and the dynamics of the bacterial population density. Analysis of the luminescence spectra of bacteria shows that luminescence occurs mainly in the blue and green regions of the spectrum with luminescence maxima in the range of 460–520 nm, but the ultra-weak glow is also registered in the UV and red spectral ranges. The variability of photobacterial luminescence spectra over time in the spectral ranges of the main luminophores causes color fluctuations between the blue and green ranges. Conclusions. The key parameters of multi-day background and short-term induced bioluminescence dynamics of photobacteria in different environments were clarified, and the certain variability of the spectral characteristics of luminescent radiation over time was shown. The revealed features of the dynamics of the bioluminescence of P. phosphoreum must be taken into account in practical application to assess the toxicity of substances of various nature, as well as in environmental monitoring.

Background: Recent studies on the lysate of Lactobacillus rhamnosus DV have demonstrated its antimicrobial and fungicidal activities. Classical microbiological methods for evaluating postbiotics and metabiotics are resource-intensive that need for new rapid and sensitive tests systems to assess their antimicrobial and antifungal properties. Objectives: The aim of this work was to study the effects of the Lactobacillus rhamnosus DV lysate on the intensity of Photobacterium phosphoreum bioluminescence and to demonstrate the potential use of bacterial bioluminescence to determine the bacteriostatic activity of this postbiotic substance. Materials and methods: The cell lysates of lactic acid bacterial strain L. rhamnosus DV were investigated, which were included in the Del-Immune V® dietary supplement produced by MirImmunoPharm LLC (Ukraine) in cooperation with Stellar Biotics, LLC (USA). The culture of P. phosphoreum IMV B-7071 was used in this study. Bioluminescence measurements were conducted using a digital photo-registration method. Bioluminescence was analyzed using cross-platform open-source software ImageJ (NIH) in brightness units in RGB color space. Results: The bioluminescence intensity initially increased with population density during the first day, then faded despite the continued growth of cell density in the bacterial suspensions. The addition of Lactobacillus rhamnosus DV lysate significantly suppressed bioluminescence, reducing it to background levels within 24 hours, with the effect varying by concentration. The peak luminescence in control samples occurred at 18 hours, whereas in lysate-treated samples it shifted to 3–6 hours, depending on the lysate concentration. Conclusions: The lysate of Lactobacillus rhamnosus DV causes a significant decrease in the growth rate of Photobacterium phosphoreum and strongly suppresses the intensity of their bioluminescence, the magnitude of which depends on the concentration of the lysate. This finding supports the use of bacterial luminescence as an effective way for evaluating the bacteriostatic activity of postbiotic substances against pathogenic and opportunistic microorganisms.

Introduction. Currently, research is being conducted to identify the mechanisms that enable living organisms to sense and utilize the Earth's magnetic field for orientation and navigation. The primary hypothetical mechanisms under active discussion include the radical pair model, which involves magnetosensitive free radical redox reactions in enzymatic systems containing oxygen molecules and flavin compounds (such as cryptochromes and bacterial luciferases), as well as the model involving intracellular magnetic magnetite particles interacting with the magnetic field. Our focus is on the first hypothesis. Therefore, the aim of our study was to investigate the effects of constant and extremely low frequency magnetic fields on the bioluminescence of Photobacterium phosphoreum, based on a flavin oxidation reaction. Notably, photobacteria are widely used as bioindicators of water pollution and indicators of exposure to various biologically active compounds. Methods. We measured the bioluminescence of P. phosphoreum in liquid media of standard composition for bacterial nutrient medium at room temperature (22-24°C). The baseline bioluminescence was evaluated over several days following inoculation in the culture medium. Bioluminescence was recorded using digital photoregistration, with subsequent image processing conducted in ImageJ or OriginPro. Magnetic field exposure was applied in two modes. In the first mode, bacterial suspensions were exposed to the magnetic field continuously from the moment of inoculation throughout the entire growth period. In the second mode, short-term magnetic field exposure was applied for several minutes after active hydrodynamic stirring of the bacterial suspension, which triggered a burst of luminescence, followed by fading and return to the baseline level. The magnetic field induction was measured using a Hall sensor. Results. Relatively strong static magnetic fields in the range of 2-8 mT weakly activated bioluminescence during the active growth phase of the bacterial population, but they statistically significantly suppressed the glow of bacteria during their maximum luminescence and subsequent dimming. The magnitude of the effects of the magnetic field was small, approximately 15% relative to the control values. The influence of a low-frequency magnetic field with a frequency of 7.85 Hz and induction of 100 μT stimulated the baseline bioluminescence of the photobacteria. At the same time, the magnetic field did not significantly affect either the concentration of oxygen or the concentration of bacterial cells in suspension, indicating a direct influence of magnetic fields on the metabolic processes associated with the bioluminescent system of bacterial cells. During short-term exposure to this extremely low frequency magnetic field, we observed a burst of luminescence initiated by the active hydrodynamic stirring of the bacterial suspension. This resulted in slow but statistically significant increase in the intensity of baseline bioluminescence by 5-10%. Conclusion. P. phosphoreum is sensitive to the action of static and extremely low-frequency fields, showing a biological efficiency within 15% of the control values. This bacterial model of magnetosensitivity is convenient for further experimental verification of the hypothesis regarding the magnetosensitivity of radical pairs. The work was supported by IEEE “Magnetism in Ukraine 2022/2023 initiative”, project “Development of a microbial test to evaluate the effect of geomagnetic field on biological systems”. Grant Agreement #99184

The metachromatic coloration of volutinous granules of the yeast Saccharomyces cerevisiae is one of the indicators of the influence of sharp geomagnetic field (GMF) perturbations. The metachromasia reaction is based on the aggregation of dye molecules in interaction with inorganic polyphosphates, which are components of volutinous granules. To determine the characteristics of the geomagnetic field that cause the appearance of different colors of the metachromasia reaction, it is necessary to simultaneously monitor this reaction and changes in the GMF. High-quality monitoring is possible with rapid automated counting of cells with all possible color changes during the metachromasia reaction. The aim of the work was to develop a neural network architecture for recognizing and quantifying color changes and heterogeneity in real time during monitoring of the metachromasia reaction of volutinous granules of the yeast S. cerevisiae, which is necessary for further determining their correlations with changes in the geomagnetic field of different intensities. A program based on a nonrecursive labeling algorithm was created to count the number of cells in the study groups. In the course of the work, the software of two neural network architectures was compared to determine the best results in recognizing and quantifying yeast cells with different colors during the volutinous granule metachromasia reaction. It was determined that the Unet architecture type coped with the tasks of cell classification and segmentation much more efficiently than the Inception v3 architecture. The average relative error for automatic recognition of all cell groups was 3.85%, and the maximum relative error was 4.56%. The performance of the neural network was 89.9% when detecting cell segmentation and 86.4% when detecting color differences in the metachromasia reaction.