Comparative Genomic and Metabolomic Characterization of Lactiplantibacillus plantarum LP140 and Bifidobacterium breve BB010 Reveals Distinct Extracellular Metabolic Signatures with Potential Relevance to Gut–Brain Axis-Associated Functions

Background. The microbiota-gut-brain axis is increasingly recognized as an important route through which intestinal bacteria may influence neurophysiology, behavior, and mental health. In this context, psychobiotics are defined as strains capable of affecting gut-brain signaling through the production or modulation of neuroactive, metabolic, and immunoregulatory molecules. However, mechanistically informed evaluation of candidate psychobiotics requires strain-level integration of genomic potential with measurable metabolic output. Here, we performed a comparative genomic and metabolomic characterization of two probiotic strains, Lactiplantibacillus plantarum LP140 and Bifidobacterium breve BB010, to assess strain-specific metabolic traits potentially relevant to functions associated with the gut–brain axis. Results. Genome mining combined with pathway reconstruction revealed distinct metabolic architectures in the two strains. LP140 showed stronger genomic support for glutamate-to-γ -aminobutyric acid (GABA) conversion, a more developed succinate-associated branch, and a broadly fermentative background. In contrast, BB010 showed greater support for nicotinate/nicotinamide-associated metabolism, including a complete de novo biosynthetic route from aspartate to nicotinamide adenine dinucleotide, together with broader anabolic capacity for selected amino acid pathways. Both strains encoded functions relevant to host interaction, including lactose/galactose utilization and bile salt hydrolase activity, whereas neither showed strong genomic support for canonical histamine or tyramine biosynthesis. Targeted extracellular metabolomics was broadly consistent with these strain-specific genomic predictions. LP140 showed marked accumulation of lactate, succinate, and GABA, consistent with a strongly fermentative extracellular metabolic profile that includes metabolites potentially relevant to the gut–brain axis. BB010, in turn, showed marked extracellular accumulation of nicotinic acid and selective increases in glutamine and glycine, indicating a distinct vitamin B3- and amino acid-centered metabolic signature. Polyamine-related profiling suggested turnover rather than robust de novo production, particularly in LP140. Conclusions. Together, these data indicate that LP140 and BB010 display distinct and potentially complementary strain-specific metabolic profiles: LP140 with a stronger GABA- and fermentation-associated signature, and BB010 with a stronger vitamin B3-associated and selective amino acid-remodeling profile. More broadly, this study provides a strain-resolved framework for evaluating microbial candidates in gut–brain-axis-oriented research.