Bacillus subtilis: Taxonomy, biology, and functional applications from kingdom to species level

Bacillus subtilis is one of the most intensively studied Gram-positive bacteria and has long served as a model organism for understanding bacterial physiology, genetics, and cellular differentiation. Its taxonomic position within the domain Bacteria reflects a highly conserved evolutionary lineage characterized by endospore formation, metabolic versatility, and remarkable environmental resilience. Beyond its foundational role in molecular biology, B. subtilis has emerged as a multifunctional microorganism with extensive applications in agriculture, food biotechnology, environmental management, and industrial fermentation. The species exhibits diverse biological traits, including rapid growth, robust stress tolerance, efficient secretion systems, and the capacity to produce a wide array of bioactive metabolites such as enzymes, antibiotics, biosurfactants, and phytohormones. These properties underpin its use as a biological control agent, plant growth–promoting bacterium, probiotic, and industrial workhorse for recombinant protein production. Recent advances in systems biology, metabolic engineering, and synthetic biology have further expanded the functional potential of B. subtilis, enabling precise manipulation of metabolic pathways and regulatory networks. This review provides a comprehensive synthesis of B. subtilis from kingdom to species level, integrating taxonomy, cellular biology, genetics, physiology, and functional applications. Emphasis is placed on contemporary research trends and applied innovations, highlighting the central role of B. subtilis in sustainable biotechnology and future bio-based industries.