Functional gene modules of lactic acid bacteria in fermented foods: Environmental regulation, validation, and synthetic community design

Background Lactic acid bacteria (LAB) are essential for the quality, safety and functionality of fermented foods, but their performance cannot be predicted from taxonomy or gene presence alone. Their functions depend on environment-responsive gene modules shaped by food matrices, physicochemical stress, nutrients and microbial interactions. Scope and approach This review synthesizes LAB functional gene modules from an environment-centered and evidence-led perspective. Dairy, meat, vegetable and cereal fermentations are compared as matrix-defined systems that select modules for carbohydrate utilization, proteolysis, stress adaptation, antimicrobial activity, texture formation and metabolite production. Regulatory effects of pH, salt, oxygen, carbon and nitrogen availability, and interspecies interactions are examined. Screening and validation strategies are organized into a five-level evidence hierarchy. Key findings and conclusions LAB functional genes should be treated as modular, context-dependent and testable units rather than static annotations. Gene presence and differential expression support candidate discovery but are insufficient for design-ready use. Functional modules require validation through genomic plausibility, responsive activity, causal function, matrix validity and community robustness. This framework can guide strain selection, targeted engineering, predictive modeling, SynCom design and safety-by-design, supporting controllable and reproducible fermented-food production.