An alternating active-dormitive strategy enables disadvantaged prey to outcompete the perennially active prey through Parrondo’s paradox

Background Dormancy is widespread in nature, but while it can be an effective adaptive strategy in fluctuating environments, the dormant forms are costly due to the inability to breed and the relatively high energy consumption. We explore mathematical models of predator-prey systems, in order to assess whether dormancy can be an effective adaptive strategy to outcompete perennially active (PA) prey, even when both forms of the dormitive prey (active and dormant) are individually disadvantaged. Results We develop a dynamic population model by introducing an additional dormitive prey population to the existing predator-prey model which can be active (active form) and enter dormancy (dormant form). In this model, both forms of the dormitive prey are individually at a disadvantage compared to the PA prey and thus would go extinct due to their low growth rate, energy waste on the production of dormant prey, and the inability of the latter to grow autonomously. However, the dormitive prey can paradoxically outcompete the PA prey with superior traits and even cause its extinction by alternating between the two losing strategies. We observed higher fitness of the dormitive prey in rich environments because a large predator population in a rich environment cannot be supported by the prey without adopting an evasive strategy, that is, dormancy. In such environments, populations experience large-scale fluctuations, which can be survived by dormitive but not by PA prey. Conclusion We show that dormancy can be an effective adaptive strategy to outcompete superior prey, recapitulating the game-theoretic Parrondo’s paradox, where two losing strategies combine to achieve a winning outcome. We suggest that the species with the ability to switch between the active and dormant forms can dominate communities via competitive exclusion.

The Abundance and Taxonomic Diversity of Filterable Forms of Bacteria during Succession in the Soils of Antarctica (Bunger Hills)

Previous studies have shown that a significant part of the bacterial communities of Antarctic soils is represented by cells passing through filters with pore sizes of 0.2 µm. These results raised new research questions about the composition and diversity of the filterable forms of bacteria (FFB) in Antarctic soils and their role in the adaptation of bacteria to the extreme living conditions. To answer such questions, we analyzed the succession of bacterial communities during incubation of Antarctic soil samples from the Bunger Hills at increased humidity and positive temperatures (5°C and 20°C). We determined the total number of viable cells by fluorescence microscopy in all samples and assessed the taxonomic diversity of bacteria by next-generation sequencing of the 16S rRNA gene region. Our results have shown that at those checkpoints where the total number of cells reached the maximum, the FFB fraction reached its minimum, and vice versa. We did not observe significant changes in taxonomic diversity in the soil bacterial communities during succession. During our study, we found that the soil bacterial communities as a whole and the FFB fraction consist of almost the same phylogenetic groups. We suppose rapid transition of the cells of the active part of the bacterial population to small dormant forms is one of the survival strategies in extreme conditions and contributes to the stable functioning of microbial communities in Antarctic soils.

Changes in the metabolism of innate immune cells of homoithermic animals infected with dormant forms of Yersinia pseudotuberculosis

Under the influence of unfavorable environmental factors, microorganisms pass into a viable, but uncultivated state and form a dormant (dormant) cellular phenotype, characterized by a lack of growth and metabolic activity. Dormant forms of bacteria are not detected by traditional microbiological methods, but they play an important role in the development of protracted and chronic infections in animals and humans. Purpose of the study: to characterize the experimental infectious process in warm-blooded animals, induced by the dormant phenotypes of Y. pseudotuberculosis, and to evaluate changes in the activity of the enzyme systems of inflammatory effector cells. For the study, bacteria were taken from a culture stored under static conditions for 10 years in a test tube under a layer of petroleum jelly at a temperature of 4–6 °C. Ultrastructural features of dormant cell forms were confirmed by transmission electron microscopy. The viability of dormant cells was assessed by the molecular genetic method (PCR). The absence of reproductive activity of the dormant phenotypes of Y. pseudotuberculosis was checked by repeated inoculations in LB broth, Endo and Serov›s media, and incubation at temperatures of 4–6, 22–24 and 37 °C. Further, the activity of the enzyme systems of cells of the inflammatory process effectors in vivo was investigated. During the experimental infection, the animals showed a gradual increase in the number of inflammatory effector cells. The prevailing number of neutrophils (65–70 %) on days 14–21 of infection indicated a developing inflammatory process. Reversion of the dormant form of Y. pseudotuberculosis in vivo and the development of an inflammatory process in the cells of the peritoneal exudate of infected animals inhibits the activity of the oxygen- and nitroxide-dependent bactericidal systems, as evidenced by the low values of lactate dehydrogenase, myeloperoxidase and nitric oxide. Thus, the data obtained indicate the possibility of reversion of the dormant forms of Y. pseudotuberculosis into vegetative forms 21 days after infection. On the part of the cells of innate immunity, modulation of the activity of intracellular enzymes, aimed at the induction of antimicrobial protection, was revealed.

Main Results of the Research on the Far Eastern Scarlet-Like Fever as a Specific Clinical and Epidemic Manifestation of Pseudotuberculosis: A Review of Comprehensive Studies

Introduction: Until 1950s, pseudotuberculosis in humans was known in the world as a sporadic disease with appendicular syndrome. In 1959, the first outbreak of a previously unknown disease called Far Eastern scarlet-like fever (FESLF) was registered in Vladivostok. The purpose of this article is to review priority achievements of the Research Institute of Epidemiology and Microbiology named after G.P. Somov in the field of studying FESLF as a specific clinical and epidemic manifestation of pseudotuberculosis in Russia. Materials and methods: The priority data were obtained based on microbiological, epidemiological, molecular genetic, as well as pathomorphological and electron microscopic studies of biological samples from human FESLF cases and experimental animals infected with Yersinia pseudotuberculosis strains with different plasmid characteristics. Results: It has been proven that the FESLF pathogen is a specific clone of Yersinia pseudotuberculosis having a certain plasmid profile pVM82, pYV 48 MDa, sequence type (2ST) and the first allele of the yadA gene. The causative agent of FESLF is characterized by the phenomenon of psychrophilicity, which consists in its ability to multiply in the environment with its biologically low and changing temperature (4–12 °C), at which the pathogen multiplies and accumulates while preserving or increasing its virulence, thus inducing the epidemic process. The article describes the main genetic and biochemical mechanisms of Y. pseudotuberculosis adaptation to changing environmental conditions, reveals morphological manifestations of the adaptive variability of these bacteria under different conditions of their habitat, and presents the main features of the pathogenesis and morphogenesis of FESLF, including those associated with plasmid characteristics and toxigenicity of Y. pseudotuberculosis. Conclusion: Currently, the epidemic process of pseudotuberculosis/FESLF is characterized by a decrease in the proportion of outbreaks and predominance of sporadic cases. The relevance of further research is associated with the study of the dormant forms of Y. pseudotuberculosis and the formation of ideas about pseudotuberculosis as a persistent infectious disease.

Three-decade failure to eradication of refractory Helicobacter pylori infec-tion and recent efforts to eradicate the infection

Background: Helicobacter pylori causes dangerous and deadly diseases such as gastric cancer and duodenal ulcers. Eradication and treatment of this bacterium are very important due to the deadly diseases caused by H. pylori and the high cost of treatment for countries. So, we present a complete list of the most important causes of failure in the treatment and eradication of H. pylori, and addresses new therapeutic methods that may be effective in controlling this bacterium in the future. Results: Many efforts have been made to control and eradicate this bacterium over the years, but no success has been achieved since its eradication is a complex process affected by the bacterial properties and host factors. Previous studies have shown that various factors are involved in failure to eradicate H. pylori, such as new genotypes of the bacterium with higher pathogenicity, inappropriate patient cooperation, mutations, biofilm formation and dormant forms that cause antibiotic resistance, acidic stomach pH, high bacterial load, smoking, immunosuppressive features and intracellular occurrence of H. pylori. On the other hand, recent studies reported that the use of probiotics, nanoparticles, antimicrobial peptides, natural product and vaccine can be helpful in the treatment and eradication of H. pylori infections. Conclusion: Eradication of H. pylori is crucial for the treatment of important diseases such as gastric cancer. Therefore, it seems that identifying the failure causes of treating this bacterium can be helpful in controlling the infections. Besides, further studies on new therapeutic strategies may help eradicate H. pylori in the future.

Induction of Plasmodium falciparum strain 2300 dormant forms by artemisinin

BACKGROUND The presence of Plasmodium falciparum resistance and decreased efficacy of artemisinin and its derivatives has resulted in the issue of malaria becoming increasingly complex, because there have been no new drugs as artemisinin replacements. The aims of this research were to evaluate in vitro changes in ultrastructural morphology of P. falciparum 2300 strain after exposure to artemisinin. METHODS The research used an experimental design with post test only control group. Cultures of P. falciparum 2300 strain in one control and one mutant group were treated by exposure to artemisinin at IC50 10-7 M for 48 hours. Ultrastructural phenotypic examination of ring, trophozoite and schizont morphology and developmental stage in the control and mutant group were done at 0, 12, 24, 36, 48 hours by making thin blood smears stained with 20% Giemsa for 20 minutes and examined using a microscope light at 1000x magnification. RESULTS Dormant forms occurred after 48 hours of incubation with IC50 10-7 M artemisinin in the control group. In the mutant group, dormant forms, trophozoites with blue cytoplasm and normal schizont developmental stages were seen. Ultrastructural phenotypic morphology at 0, 12, 24, 36, 48 hours showed that in the control group dormant formation already occurred with exposure to IC50 10-7 M, while in the mutant group dormant formation occurred only with exposure to IC50 2.5x10-5 M. CONCLUSION Exposure to artemisinin antimalarials in vitro can cause phenotypic morphological changes of dormancy in P. falciparum Papua 2300 strain.