The Eukaryotic Host-Microbe-Phage-Nutrition Interplay Determines the Bacterial Effectors of Supplemental Lysine's Health Benefits: An Experimental Cellular Senescence Model of Digestive Conditions in Older Adults.

Recently, the consumption of various forms of the nutritive amino acid lysine (e.g., nutraceuticals and dietary supplements) has increased, particularly among the elderly, as it cannot be synthesized by the human body and plays a crucial role in several cellular physiological processes, including intestinal calcium and iron absorption, proteinogenesis, and fatty acid metabolism. However, the biochemical and immunological events that occur within the eukaryotic host-microbe-phage-nutrition interaction, especially when high amounts of lysine are consumed in nutraceutical or dietary supplement form by the elderly due to age-related requirements, as well as the impact on gut bacteria-derived metabolites, have not yet been fully studied. We hypothesized that (1) within an infectious-inflamed digestive milieu, the metabolism of excess extracellular lysine differs between young and senescent digestive cells, and (2) phages within the milieu exhibit alterations in host-microbe cometabolite signal profiles. To address this, we examined how gut microbes and phages, key regulators of eukaryotic host physiology, influence the immunometabolism of excess lysine. By combining two models of young and senescent digestive cells, the pathogenic P. aeruginosa PAO1, the Pseudomonas phage KPP22, and the anti-inflammatory bacterium Intestinimonas butyriciproducens, and simulating the pathogenesis of the interactive process of excessive lysine ingestion, we developed a five-way screening approach to explore key cell readouts, including viability, integrity, and function of the epithelial barrier, as well as cellular immunometabolic responses to exogenous lysine supplementation in cultures under infectious inflammation. Our findings are consistent with the possibility that host-microbe-microbe interactions involving lysine utilization and cross-feeding may influence the effects of lysine supplementation. These effects, whether beneficial or detrimental, can depend on the bacterial community, including the presence of pathogenic or potentially beneficial bacteria, interactions with intestinal phages, and the physiological conditions and metabolic requirements of the host and individual microbial taxa.