Lactic acid bacteria: Taxonomy, physiology, and functional roles

Lactic acid bacteria (LAB) represent a diverse group of Gram-positive microorganisms that play essential roles in food fermentation, human and animal health, agriculture, and industrial biotechnology. Characterized primarily by their ability to produce lactic acid as a major end product of carbohydrate metabolism, LAB have been exploited for centuries in traditional fermented foods and, more recently, in modern biotechnological applications. Advances in microbial taxonomy, molecular biology, and functional genomics have substantially expanded understanding of LAB diversity, physiology, and ecological significance. However, the functional roles of LAB extend far beyond acid production, encompassing antimicrobial activity, probiotic effects, bio-preservation, and contributions to food safety and nutritional quality. This review provides a comprehensive synthesis of lactic acid bacteria, focusing on their taxonomy, physiological characteristics, and functional roles across food, health, agricultural, and industrial systems. Major LAB genera are discussed in relation to classification criteria, metabolic pathways, and stress tolerance mechanisms. The functional contributions of LAB to food fermentation, probiotic activity, pathogen inhibition, and sustainable bioprocessing are critically examined. Current challenges, knowledge gaps, and future perspectives for LAB research and application are also highlighted. This review aims to provide an integrated reference for researchers, students, and practitioners seeking to understand the biological and applied significance of lactic acid bacteria.