Bacillus subtilis

RANK: Species

TAXONOMY: Firmicutes -> Bacilli -> Bacillales -> Bacillaceae -> Bacillus -> Bacillus subtilis group -> Bacillus subtilis


Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants and humans. A member of the genus Bacillus, B. subtilis is rod-shaped, and can form a tough, protective endospore, allowing it to tolerate extreme environmental conditions. B. subtilis has historically been classified as an obligate aerobe, though evidence exists that it is a facultative aerobe. B. subtilis is considered the best studied Gram-positive bacterium and a model organism to study bacterial chromosome replication and cell differentiation. It is one of the bacterial champions in secreted enzyme production and used on an industrial scale by biotechnology companies. This species is commonly found in the upper layers of the soil, and evidence exists that B. subtilis is a normal gut commensal in humans. A 2009 study compared the density of spores found in soil (about 106 spores per gram) to that found in human feces (about 104 spores per gram). The number of spores found in the human gut was too high to be attributed solely to consumption through food contamination. Cultures of B. subtilis were popular worldwide before the introduction of antibiotics as an immunostimulatory agent to aid treatment of gastrointestinal and urinary tract diseases. It was used throughout the 1950s as an alternative medicine, which upon digestion has been found to significantly stimulate broad-spectrum immune activity including activation of secretion of specific antibodies IgM, IgG and IgA and release of CpG dinucleotides inducing INF A/Y producing activity of leukocytes and cytokines important in the development of cytotoxicity towards tumor cells. It was marketed throughout America and Europe from 1946 as an immunostimulatory aid in the treatment of gut and urinary tract diseases such as Rotavirus and Shigellosis, but declined in popularity after the introduction of antibiotics, despite causing fewer allergic reactions and significantly lower toxicity to normal gut flora. It is still widely used in Western Europe and the Middle East as an alternative medicine.

This species has been identified as a resident in the human gastrointestinal tract based on the phylogenetic framework of its small subunit ribosomal RNA gene sequences.[PMC 4262072]

Gut associated
Type species
Fecal distribution

Bacillus subtilis growth inhibited by
  • Paenibacillus polymyxa


    Metabolic Endproducts
  • 2,3-Butanediol
  • Pyridoxine (Vitamin B6)

  • Growth Inhibited by
  • Hypericin

  • Biotransforms
  • Tannin