The genus Bacillus is a phenotypically large, heterogeneous collection of gram-positive or gram-variable spore-forming, aerobic or facultative anaerobic bacteria. Ubiquitous in nature, Bacillus includes both free-living (nonparasitic) species and two parasitic pathogenic species. These two Bacillus species are medically significant: B. anthracis causes anthrax, and B. cereus causes food poisoning.
For their wide range of physiologic characteristics and ability to produce a multitude of secretory proteins, enzymes, antimicrobial compounds, vitamins, and carotenoids, Bacillus species are used in many medical, pharmaceutical, agricultural, and industrial processes. Besides the commonly explored strains, bacterial spore formers, most of the genus Bacillus does carry probiotic attributes. Bacilli are gaining interest in human-health related functional food research coupled with their enhanced tolerance and survivability under a hostile environment of the gastrointestinal tract. Besides, Bacilli are more stable during processing and storage of food and pharmaceutical preparations, making them a more suitable candidate for health-promoting formulations. Further, Bacillus strains also possess biotherapeutic potential, which is connected with their ability to interact with the internal milieu of the host by producing a variety of antimicrobial peptides and small extracellular effector molecules.