Probiotics under Selective Pressure: Novel Insights and Biosafety Challenge.

The advent of novel high-resolution physicochemical techniques and the integration of omics technologies into biomedical research have opened avenues for investigating the mechanisms underlying bacterial survival in vitro and in vivo, subjected to the influence of biotic and abiotic stressors. This encompasses axenic cultures, microbial communities, and holobionts. The development of innovative methodological platforms has facilitated the acquisition of unique data relevant to both fundamental and applied scientific fields. The experimental results indicated a remarkably high level of genomic plasticity in microorganisms and the potential for the evolution of bacterial virulence under selective pressure. These findings have significantly impacted our understanding of the arsenal of self-defense tools in bacteria and the prioritization of research in this field. The increasing quantity of factual material now necessitates a shift in focus from pathogens to the broader category of commensal bacteria, which are used as probiotics in various fields, including medicine, agriculture, and the food industry. The possibility of large-scale genomic reorganization and progressive evolution of virulence in these bacteria under stressful conditions, as well as their modulation of host cell signaling systems and suppression of innate immunity, negative regulation of key cell cycle controllers, disruption of the structure of the intestinal microbiota and intestinal homeostasis, highlight the obvious insufficiency of our knowledge about the "logic of life" of symbionts and the mechanisms of their interaction with eukaryotic cells. This may compromise the ideas of several practical applications. This underscores the importance of comprehensive studies of commensals, their potential for plasticity in different environmental conditions, and the ways in which they communicate and interact with regulatory networks of higher organisms. It also highlights the need to develop a standardization for assessing the safety of probiotics. The review addresses these issues.