| Bacillus subtilis | ||||||||||||||
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| Bacillus subtilis (Ehrenberg 1835) Cohn 1872 |
Bacillus subtilis is a Gram-positive, catalase-positive bacterium commonly found in soil.[1] A member of the genus Bacillus, B. subtilis has the ability to form a tough, protective endospore, allowing the organism to tolerate extreme environmental conditions. Unlike several other well-known species, B. subtilis has historically been classified as an obligate aerobe, though recent research has demonstrated that this is not strictly correct.[2]
It has also been called Hay bacillus or Grass bacillus. It is bacillus because the bacterium is rod shaped or bacilli shaped.
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B. subtilis is not considered a human pathogen; it may contaminate food but rarely causes food poisoning.[3] B. subtilis produces the proteolytic enzyme subtilisin. B. subtilis spores can survive the extreme heating that is often used to cook food, and it is responsible for causing ropiness — a sticky, stringy consistency caused by bacterial production of long-chain polysaccharides — in spoiled bread dough.
B. subtilis can divide asymmetrically, producing an endospore that is resistant to environmental factors such as heat, acid, and salt, and which can persist in the environment for long periods of time. The endospore is formed at times of nutritional stress, allowing the organism to persist in the environment until conditions become favorable. Prior to the decision to produce the spore the bacterium might become motile, through the production of flagella, and also take up DNA from the environment.
Bacillus subtilis duplicates its single circular chromosome by initiating DNA replication at a single locus, the origin (oriC). Replication proceeds bidirectionally and two replication forks progress in the clockwise and counterclockwise directions along the chromosome halves. Chromosome replication is completed when the forks reach the terminus region, which is positioned opposite to the origin on the chromosome map, and contains several short DNA sequences (Ter sites) that promote replication arrest. Specific proteins mediate all the steps in DNA replication. The comparison between the sets of proteins involved in chromosomal DNA replication in B. subtilis and in Escherichia coli reveals both similarities and differences. Although the basic components promoting initiation, elongation, and termination of replication are well conserved, some important differences can be found (such as one bacterium missing proteins essential in the other). These differences underline the diversity in the mechanisms and strategies that various bacterial species have adopted to carry out the duplication of their genomes.[4]
B. subtilis has proven highly amenable to genetic manipulation, and has therefore become widely adopted as a model organism for laboratory studies, especially of sporulation, which is a simplified example of cellular differentiation. It is also heavily flagellated, which gives B.subtilis the ability to move quite quickly. In terms of popularity as a laboratory model organism B. subtilis is often used as the Gram-positive equivalent of Escherichia coli, an extensively studied Gram-negative rod.
B. subtilis is used as a soil inoculant in horticulture and agriculture. B. subtilis has been used for a biowarfare simulant during Project SHAD (aka Project 112).[1] B. subtilis hazard status is under dispute.[2]
Enzymes produced by B. subtilis and B. licheniformis are widely used as additives in laundry detergents.
Its other uses include the following:
B. subtilis has approximately 4,100 genes. Of these, only 192 were shown to be indispensable; another 79 were predicted to be essential as well. A vast majority of essential genes were categorized in relatively few domains of cell metabolism, with about half involved in information processing, one-fifth involved in the synthesis of cell envelope and the determination of cell shape and division, and one-tenth related to cell energetics.
In 1835, the bacterium was originally named Vibrio subtilis by Christian Gottfried Ehrenberg,[5] and renamed Bacillus subtilis by Ferdinand Cohn in 1872.[6]