TAXONOMY: Bacteria -> Terrabacteria group -> Firmicutes -> Bacilli -> Bacillales -> Bacillaceae -> Bacillus
'Bacillus' is a genus of Gram-positive, rod-shaped (bacillus) bacteria and a member of the phylum Firmicutes. Bacillus species can be obligate aerobes (oxygen reliant), or facultative anaerobes (having the ability to be aerobic or anaerobic). They will test positive for the enzyme catalase when there has been oxygen used or present. Ubiquitous in nature, Bacillus includes both free-living (nonparasitic) and parasitic pathogenic species. Under stressful environmental conditions, the bacteria can produce oval endospores that are not true 'spores', but to which the bacteria can reduce themselves and remain in a dormant state for very long periods. These characteristics originally defined the genus, but not all such species are closely related, and many have been moved to other genera of the Firmicutes. Many species of Bacillus can produce copious amounts of enzymes which are made use of in different industries. Some species can form intracellular inclusions of polyhydroxyalkanoates under certain adverse environmental conditions, as in a lack of elements such as phosphorus, nitrogen, or oxygen combined with an excessive supply of carbon sources. B.subtilis has proved a valuable model for research. Other species of Bacillus are important pathogens, causing anthrax and food poisoning.
Cells rod-shaped, straight or slightly curved, occurring singly and in pairs, some in chains, and occasionally as long filaments. Endospores are formed, no more than one to a cell; these spores are very resistant to many adverse conditions. Gram-positive, or Gram-positive only in early stages of growth, or Gram-negative. A meso-DAP direct murein cross-linkage type is commonest, but l-Lys-d-Glu, Orn-d-Glu and l-Orn-d-Asp have occasionally been reported. Motile by means of peritrichous or degenerately peritrichous flagella, or nonmotile. Aerobes or facultative anaerobes, but a few species are described as strictly anaerobic. The terminal electron acceptor is oxygen, replaceable by alternatives in some species. Most species will grow on routine media such as nutrient agar and blood agar. Colony morphology and size very variable between and within species. A wide diversity of physiological abilities is exhibited, ranging from psychrophilic to thermophilic, and acidophilic to alkaliphilic; some strains are salt tolerant and some are halophilic. Catalase is produced by most species. Oxidase-positive or -negative. Chemo-organotrophic; two species are facultative chemolithotrophs: prototrophs to auxotrophs requiring several growth factors. Mostly isolated from soil, or from environments that may have been contaminated directly or indirectly by soil, but also found in water, food and clinical specimens. The resistance of the spores to heat, radiation, disinfectants, and desiccation results in species being troublesome contaminants in operating rooms, on surgical dressings, in pharmaceutical products and in foods. Most species have little or no pathogenic potential and are rarely associated with disease in humans or other animals; an exception is Bacillus anthracis, the agent of anthrax; several other species may cause food poisoning and opportunistic infections, and strains of Bacillus thuringiensis are pathogenic to invertebrates.DNA G + C content (mol%): 32–66 (Tm ). Type species: Bacillus subtilis
This genus contains microbial species that can reside in the human gastrointestinal tract. [PMC 4262072]