What is Bacillus subtilis?
Bacillus subtilis is a species of bacteria in the genus bacillus. These bacteria are found in a wide variety of environments, and most literature considers bacillus species to be soil-dwelling. Interestingly, the ubiquity of bacillus species in the soil may be due to spores from the bacteria entering the environment through feces. Like many species of bacteria, members of the bacillus genus are capable of forming spores. Spores are dormant forms of the organism with very little metabolic activity. These cells function to resist harsh environments until conditions for favorable growth are sensed. The human small intestine is speculated to contain billions of bacillus species cells, many of which are B. subtilis variants.
Bacillus subtilis in Probiotics
Bacillus species are of particular interest as potential probiotics. Probiotics are ingestible bacteria which improve intestinal balance, modulate immune function, produce compounds with systemic effects, and convey some benefit to the host. Due to the pathogenic nature of many bacteria the human gut comes in contact with, the stomach contains hydrochloric acid (HCl) to protect the body from pathogens by killing off “bad” bacteria. B. subtilis spores survive transit through stomach HCl, making them particularly intriguing as a component of probiotic formulas. Once in the small intestine, B. subtilis spores sense a favorable environment for proliferation and undergo differentiation into active bacterial cells. It is here that these bacterial communities begin to flourish and convey benefits to the host.
Variants and Subtypes
There are several variants and subtypes of the species Bacillus subtilis. Some studies conducted on the efficacy of B. subtilis as a probiotic identify which variant of the species was examined. However, some studies simply refer to the bacteria as B. subtilis with no specified variant. It is likely that many of the variants produce the same biological outcomes when ingested as a probiotic, but it is important to note that there may be some variation in the mechanism of action among different subtypes. Where possible in the following statements, the subtype of B. subtilis being referenced will be noted.
Antibiotic Properties of Bacillus subtilis
Many antibiotics used pharmaceutically are actually derived from natural compounds made by bacteria. Bacteria produce antibiotics to kill off or inhibit the growth of competitors in the habitat. Bacillus subtilis strain 2335 produces a compound called aminocoumarin A, an effective antibiotic against Heliobacter pylori. Another variant of B. subtilis produced during soybean fermentation, B. subtilis var. natto, is shown to inhibit growth of the pathogenic fungus Candida. It is important to note that B. subtilis may convey some protection against pathogens. However, nearly all of the subtypes studied show little to no antibiotic resistance. Thus, probiotic supplementation with B. subtilis is likely more effective before and after, as opposed to in conjunction with, antibiotic use.
Role of Bacillus subtilis on the Immune system
In addition to producing compounds for defense against pathogens, B. subtilis has been shown to strengthen its host’s immune system. Secretory IgA (SIgA) is a type of immunoglobin responsible for protecting the gastrointestinal and respiratory tracts from pathogens. A study conducted on probiotic supplementation with B. subtilis strain CUI and immune function in an elderly population had the following highlights:
- SIgA levels in stool increased by 65% after 10 days of subtilis CUI probiotic supplementation
- SIgA levels in stool increased by 87% after 18 days of subtilis CUI probiotic supplementation
- A 20% increase in salivary SIgA levels is associated with a significantly reduced chance of contracting a cold or flu
- subtilis CUI increased salivary SIgA by 45%
Beneficial Impacts of Bacillus subtilis on Gut Health
The importance of the digestive tract in overall health and wellbeing has been a hugely popular area of research in recent years. Some studies have shed light on the beneficial impacts of B. subtilis on gut health. Gut-associated lymphoid tissue (GALT) lines the digestive tract and is an important part of the immune system as a barrier for pathogens. In a study conducted on rabbits by Rhee et. al. (2004), researchers found that B. subtilis is not only beneficial for GALT function, it is likely necessary for GALT to develop properly. Another study conducted by Williams (2007) found that B. subtilis protects the intestinal epithelial cells from oxidative damage. Bacteria use a mechanism called quorum sensing to communicate with one another. Typically, quorum sensing involves the release of small particles by one bacterial cell, which are sensed by another. B. subtilis releases a molecule called competence/sporulation stimulating factor (CSF) to communicate to nearby cells. CSF has been shown to induce the activity of heat-shock-inducible protein 27 (Hsp27) in humans. Hsp27 is largely important in protecting human intestinal cells from oxidative injury.
Research conducted on B. subtilis as a probiotic shows that it is likely effective in boosting immune activity, protecting the body from pathogens, and improving gut health. The bottom line: as spore-forming bacteria, B. subtilis can survive the harsh environment of the stomach and then colonize the small intestine, where it conveys its benefits to the host!
 Hong, H. A., Khaneja, R., Tam, N. M., Cazzato, A., Tan, S., Urdaci, M., … & Cutting, S. M. (2009). Bacillus subtilis isolated from the human gastrointestinal tract. Research in microbiology, 160(2), 134-143.
 Tan, I. S., & Ramamurthi, K. S. (2014). Spore formation in Bacillus subtilis. Environmental Microbiology Reports, 6(3), 212–225. http://doi.org/10.1111/1758-2229.12130
 Hong (2009), op. cit.
 Guo, M., Wu, F., Hao, G., Qi, Q., Li, R., Li, N., … Chai, T. (2017). Bacillus subtilis Improves Immunity and Disease Resistance in Rabbits. Frontiers in Immunology, 8, 354. http://doi.org/10.3389/fimmu.2017.00354
 Guo, Ibid.
 Hong, H. A., Duc, L. H., & Cutting, S. M. (2005). The use of bacterial spore formers as probiotics. FEMS microbiology reviews, 29(4), 813-835.
 Hong (2005), Ibid.
 Hong (2005), Ibid.
 Hong (2005), Ibid.
 Guo, op. cit.
 Lefevre, M., Racedo, S. M., Ripert, G., Housez, B., Cazaubiel, M., Maudet, C., … Urdaci, M. C. (2015). Probiotic strain Bacillus subtilis CU1 stimulates immune system of elderly during common infectious disease period: a randomized, double-blind placebo-controlled study. Immunity & Ageing : I & A, 12, 24. http://doi.org/10.1186/s12979-015-0051-y
 Lefevre, Ibid.
 Rhee, K. J., Sethupathi, P., Driks, A., Lanning, D. K., & Knight, K. L. (2004). Role of commensal bacteria in development of gut-associated lymphoid tissues and preimmune antibody repertoire. The Journal of Immunology, 172(2), 1118-1124.
 Williams, P. (2007). Bacillus subtilis: a shocking message from a probiotic. Cell host & microbe, 1(4), 248-249. https://doi.org/10.1016/j.chom.2007.05.010
 Williams, Ibid.
Disclaimer: The information provided is only intended to be general educational information to the public. It does not constitute medical advice. If you have specific questions about any medical matter or if you are suffering from any medical condition, you should consult your doctor or other professional healthcare provider.