Bacillus is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum Bacillota, with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural Bacilli is the name of the class of bacteria to which this genus belongs. Bacillus species can be either obligate aerobes which are dependent on oxygen, or facultative anaerobes which can survive in the absence of oxygen. Cultured Bacillus species test positive for the enzyme catalase if oxygen has been used or is present.
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
Bacillus cereus is a Gram-positive rod-shaped bacterium commonly found in soil, food, and marine sponges. The specific name, cereus, meaning "waxy" in Latin, refers to the appearance of colonies grown on blood agar. Some strains are harmful to humans and cause foodborne illness due to their spore-forming nature, while other strains can be beneficial as probiotics for animals, and even exhibit mutualism with certain plants. B. cereus bacteria may be anaerobes or facultative anaerobes, and like other members of the genus Bacillus, can produce protective endospores. They have a wide range of virulence factors, including phospholipase C, cereulide, sphingomyelinase, metalloproteases, and cytotoxin K, many of which are regulated via quorum sensing. B. cereus strains exhibit flagellar motility.
An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form, but it is not a true spore. It is a stripped-down, dormant form to which the bacterium can reduce itself. Endospore formation is usually triggered by a lack of nutrients, and usually occurs in gram-positive bacteria. In endospore formation, the bacterium divides within its cell wall, and one side then engulfs the other. Endospores enable bacteria to lie dormant for extended periods, even centuries. There are many reports of spores remaining viable over 10,000 years, and revival of spores millions of years old has been claimed. There is one report of viable spores of Bacillus marismortui in salt crystals approximately 250 million years old. When the environment becomes more favorable, the endospore can reactivate itself into a vegetative state. Most types of bacteria cannot change to the endospore form. Examples of bacterial species that can form endospores include Bacillus cereus, Bacillus anthracis, Bacillus thuringiensis, Clostridium botulinum, and Clostridium tetani. Endospore formation is not found among Archaea.
Clostridium is a genus of anaerobic, Gram-positive bacteria. Species of Clostridium inhabit soils and the intestinal tract of animals, including humans. This genus includes several significant human pathogens, including the causative agents of botulism and tetanus. It also formerly included an important cause of diarrhea, Clostridioides difficile, which was reclassified into the Clostridioides genus in 2016.
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, humans and marine sponges. As 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 anaerobe. 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.
Bacillus coagulans is a lactic acid–forming bacterial species first isolated and described in 1915 by B.W. Hammer at the Iowa Agricultural Experiment Station as a cause of an outbreak of coagulation in evaporated milk packed by an Iowa condensary. Separately isolated in 1935 and described as Lactobacillus sporogenes in the fifth edition of Bergey's Manual of Systematic Bacteriology, it exhibits characteristics typical of both genera Lactobacillus and Bacillus; its taxonomic position between the families Lactobacillaceae and Bacillaceae was often debated. However, in the seventh edition of Bergey's, it was finally transferred to the genus Bacillus. DNA-based technology was used in distinguishing between the two genera of bacteria, which are morphologically similar and possess similar physiological and biochemical characteristics.
Bacillus megaterium is a rod-like, Gram-positive, mainly aerobic, spore forming bacterium found in widely diverse habitats. It has a cell length up to 4 µm and a diameter of 1.5 µm, which is quite large for bacteria. The cells often occur in pairs and chains, where the cells are joined together by polysaccharides on the cell walls.
Bacillus oleronius is a Gram-negative bacterium belonging to the genus Bacillus. However, Bacillus oleronius has Gram-positive cell wall components shared among all bacillus species. It was first described in 1995 and was found in the hindgut of the termite Reticulitermes flavipes. It is also found in the human skin parasitic mite Demodex folliculorum, and may be related to the development of a type of rosacea.
Oritavancin, sold under the brand name Orbactiv among others, is a semisynthetic glycopeptide antibiotic medication for the treatment of serious Gram-positive bacterial infections. Its chemical structure as a lipoglycopeptide is similar to vancomycin.
Alkalihalobacillus clausii or its old scientific name Bacillus clausii is a rod-shaped, motile, and spore-forming bacterium that lives in the soil but is also a natural microflora of the mammalian gastrointestinal tract. It is classified as probiotic microorganism that maintains a symbiotic relationship with the host organism. It is currently being studied in relation to respiratory infections and some gastrointestinal disorders. Bacillus clausii has been found to produce antimicrobial substances that are active against gram-positive bacteria including Staphylococcus aureus, Enterococcus faecium and Clostridium difficile. It is sold as an anti-diarrhoea and under the brand name Erceflora by Sanofi.
Clostridium tertium is an anaerobic, motile, gram-positive bacterium. Although it can be considered an uncommon pathogen in humans, there has been substantial evidence of septic episodes in human beings. C. tertium is easily decolorized in Gram-stained smears and can be mistaken for a Gram-negative organism. However, C.tertium does not grow on selective media for Gram-negative organisms.
Bacillus horikoshii is a facultative anaerobe bacterium. It is a gram positive, alkaliphilic and alkalitolerant, aerobic endospore-forming bacteria.
Bacillus nealsonii is a species of bacteria first isolated from a spacecraft-assembly facility. Its spores are γ-radiation resistant. It is Gram-positive, facultatively anaerobic, rod-shaped and produces endospores. Its type strain is FO-92T.
Paenibacillus macerans is a diazotroph bacterium found in soil and plants capable of nitrogen fixation and fermentation. This bacteria was originally discovered in 1905 by an Austrian biologist named Schardinger and thought to be a bacillus.
Caldalkalibacillus is an aerobic and spore-forming genus of bacteria from the family of Bacillaceae the stains either Gram-positive or Gram-variable. The type species of this genus is Caldalkalibacillus thermarum.
Salisediminibacterium is a genus of Gram-positive bacteria from the family of Bacillaceae. The type species is Salisediminibacterium halotolerans.
Bacillus flexus is an aerobic, Gram-variable, rod-shaped, endospore-forming, oxidase-positive bacterium. The endospores are ellipsoidal, located in central/paracentral, unswollen sporangia. In laboratory conditions, it produces opaque, creamish, raised-margin colonies at 30 ± 2°C when incubated for 24–72 hrs. on tryptic soy agar. This bacterial species may be isolated from feces (poultry) and soil.
Metabacillus is a genus of rod-shaped bacteria exhibiting Gram-positive or Gram-variable staining in the family Bacillaceae within the order Bacillales. The type species for this genus is Metabacillus fastidiosus.
Niallia is a genus of Gram-Positive rod-shaped bacteria in the family Bacillaceae from the order Bacillales. The type species of this genus is Niallia circulans.
