Cobalamin in Porphyromonas gingivalis Pathogenicity - Project Summary Periodontitis is a polymicrobial-driven and prevalent inflammatory disease of the tissues supporting the teeth in adults with adverse effects on overall human health. Studies have revealed that cobalamin (vitamin B12) transporters are highly active in the periodontal microbiome associated with the periodontal pockets of individuals with periodontitis. Yet, the functional correlation between cobalamin utilization and the pathogenic potential of periodontal pathogens remains largely unknown. Our studies have elucidated an interconnection between cobalamin utilization, stress responses, and the virulence potential of Porphyromonas gingivalis (Pg), a key periodontal pathogen in periodontitis disease. As a potent redox sensor, cobalamin promotes cellular homeostasis under redox-changing stresses caused by nutritional limitation and reactive oxygen species (ROS). These stressors represent intrinsic attributes of the inflammatory mechanisms to eliminate infections. Based on our findings and that cobalamin plays a significant role in maintaining cellular homeostasis under redox- changing stresses, we hypothesize that cobalamin acts as a key redox-active mediator orchestrating genomic and metabolic adaptations, thereby enabling the pathogen to overcome diverse stresses and foster pathogenicity. To investigate this hypothesis, we propose two specific aims. Specific Aim 1. The impact of cobalamin on the genomic-metabolic adaptations in Pg strain 381 under stress conditions. This aim will investigate; i) the impact of cobalamin on the gene expression profile of Pg under two separate biologically relevant stresses, including iron limitation and ROS availability. To this end we will perform RNA sequencing, followed by RT-qPCR-based validation; and ii) the impact of cobalamin on the metabolic profile of Pg cells grown under the stress conditions by performing untargeted and targeted metabolomic analyses. Overall, this aim will greatly inform about the intricate connections between cobalamin utilization and the genomic-metabolic adaptations in Pg under biologically relevant stress conditions. Specific Aim 2. To understand cobalamin- regulated virulence potential and survival of Pg strain 381 in the presence of host defense mechanisms. We will determine: i) the effect of cobalamin on the virulence potential of Pg cells mediated by proteases, known as gingipains; and ii) the impact of cobalamin on the survival of Pg and its immunostimulatory potential using whole blood killing and neutrophil assays. This aim will enable us to determine the impact of cobalamin on Pg's ability to survive within the host and modulate its pathogenic potential. Upon completion of the proposed studies, for the first time, we will uncover the biological significance of cobalamin utilization in Pg's survival and pathogenesis during infection. Understanding the role of cobalamin in the pathogenesis of periodontal pathogens has the potential to open new avenues for therapeutic interventions in periodontal disease.
