Bacillus (bacteria)

Bacillus is a genus of bacteria that includes many species that are pathogenic to humans, as well as many others that are important parts of medical research. Part of family Bacillaceae, in order Bacillales, in class Bacilli, in phylum Firmicutes, Bacillus bacteria include well-known species like B. anthracis (the species responsible for anthrax) and B. cereus (responsible for many forms of food poisoning). When the term "Bacillus" is italicized and capitalized, it refers to the genus; when it is neither, it refers to a characteristic shared by many bacteria, that of being rod-shaped. All Bacillus are bacillus, but not all bacillus are in genus Bacillus. Non-Bacillus bacillus include the Salmonella genus, for instance, and the Escherichia genus that includes E. coli. All Bacillus are also Gram-positive, which indicates the presence of a peptidoglycan layer in the cell wall, rather than an outer cell membrane. Lack of that membrane makes Gram-positive bacteria more vulnerable to antibiotics.

Background

Bacillus is one of six genera that are usually pathogenic in humans, along with Streptococcus, Staphylococcus, Corynebacterium, Listeria, and Clostridium, but includes non-harmful species as well. The Bacillus genus was originally named and described by Christian Gottfried Ehrenberg in 1835, and further refined by Ferdinand Crohn in 1872. It is generally true in the history of biology that the earliest bacteria identified are among the most common in human-occupied parts of the world, and the species of genus Bacillus include many of the most ubiquitous bacteria. When originally defined, the genus was characterized by its abilities to create endospores when stressed (protecting it from hostile environments) and to go dormant for a long period of time. Modern science, however, has reclassified many bacteria species with those characteristics in other genuses.

The "type species" of Bacillus is B. subtilis. Type species are those which are permanently linked to a certain genus – that is, while taxonomy and nomenclature change over time as we come to better understand the subjects they classify, Bacillus by definition will always be the genus that includes B. subtilis. One reason for selecting subtilis (which Gottfried originally classified in the Vibrio genus) as the type species is its usefulness as a model organism, an organism that can be studied in vivo in order to observe and test biological phenomena. B. subtilis is used in the biotech industry for its enzyme production. It can be found in both soil and the human gut, and is one of the major bacteria involved in food spoilage. Studies in the twenty-first century have indicated that its population in human feces is too high to be attributable solely to contaminated food; instead, it is believed to be one of the organisms that constitute the gut flora of humans, living in a complex and not yet fully understood community of microorganisms within the digestive tract. This community performs functions that are critical to the digestion, nutrition, metabolism, and immune response of the human host.

Overview

Bacteria from the Bacillus genus are used in numerous areas of study and technology beyond medical study. B. thuringiensis (Bt) has been adopted as a pesticide that can be an important part of an integrated pest management (IPM) program. Bacterial pesticides have the benefit of being highly specific in their toxicity, whereas traditional chemical pesticides have usually been broadly toxic, which endangers local flora, can seep into the water table, and can be passed on to the consumer if crops are insufficiently washed. Bt is toxic to many of the insect species that may feed on or harm plant crops, and most studies support manufacturers' claims that it has no ill effect on higher organisms. Skeptics counter that the body of evidence is insufficient. Bt-based pesticides are sold under several trade names, two of the best known of which are Thuricide and Dipel.

Many bacteria species, including some of the Bacillus genus, are used to produce various substances of use to industry, including enzymes, organic acids, ethanol, and acetone. Bacteria can be used to produce pure chemical substances for industries where standards of purity are especially high. B. coagulans, which produces lactic acid, is used both as a probiotic (increasing the gut flora health) for various species of livestock and in the medical treatment of humans, such as to treat the symptoms of irritable bowel syndrome. B. subtilis alone is used not only as a pesticide against certain plant diseases, but also for bioremediation of dangerous explosive compounds, as part of the handling of radionuclide waste disposal, to produce certain enzymes for industry, to produce fermented foods such as Japanese natto and Korean cheonggukjang on an industrial scale, and to speed the growth of saffron. B. subtilis has been used as a test species by NASA and the aerospace industry since the 1960s.

Bacteria are also used for bioremediation, the management of waste through the introduction of organisms that remove, convert, or neutralize that waste. B. subtilis has been studied for use in bioremediation of crude oil, and B. cereus has been studied for bioremediation of pulp and paper waste. In some ways bioremediation is seen as the modern descendant of a much older practice: the compost pile, a collection of agricultural or food waste that is left to break down into rich soil. Composting was recorded by Pliny the Elder in the first century C.E., and originated even earlier. It is made possible through the bacteria that thrive in the compost, producing heat and carbon dioxide as they consume the compounds that serve as nutrients for them. More than three-quarters of these bacteria are typically Bacillus.

Lastly, along with viruses and fungi, bacteria are used as toxins in the creation of bioweapons, which are banned by the 1972 Biological Weapons Convention but have been developed in the labs of a number of countries. One of the most significant such agents is B. anthracis, the bacteria that causes the anthrax disease. Anthrax has been weaponized successfully by the United States, the United Kingdom, Japan, and Iraq, and is believed to have first been used in warfare in 1916. A trial of weaponized anthrax in Britain in 1942 resulted in Guinard Island being quarantined for 48 years.

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