Bridging In Vitro Functionality and Genomic Insights in Lactiplantibacillus plantarum L3 Isolated from Traditional Bulgarian Katak.

Katak, a traditional Bulgarian fermented dairy product distinguished by its unique sensory characteristics and extended shelf life, represents a valuable source of autochthonous microorganisms whose functional and genomic properties remain insufficiently explored. In the present study, strain L3, isolated from katak, was comprehensively characterized by a polyphasic approach integrating classical microbiological methods, molecular identification, and whole-genome sequencing. Functional assessment revealed a broad spectrum of antimicrobial activity against pathogenic bacteria and food-associated fungi, accompanied by pronounced radical-scavenging and antioxidant capacities. The strain also exhibited high transit tolerance in simulated gut passage and a favorable antibiotic susceptibility profile, indicating its potential as a probiotic candidate. Whole-genome sequencing confirmed the taxonomic affiliation of the isolate as Lactiplantibacillus plantarum and enabled the identification of genetic determinants associated with stress response, environmental adaptation, oxidative stress protection, biofilm formation, and antimicrobial activity. The genomic analysis complemented the in vitro findings by identifying genetic determinants consistent with the observed phenotypic traits, supporting the genetic potential of strain L3 for probiotic-associated functions. The integration of phenotypic and genomic evidence allowed a comprehensive evaluation of L. plantarum L3 and demonstrated that its probiotic-related properties are underpinned by a diverse repertoire of functional genes. These findings identify L3 as a promising candidate for further biotechnological/probiotic assessment.