Bacillus subtilis



Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and 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.

Pathogenesis
B. subtilis is not a human pathogen. It may contaminate food but rarely causes food poisoning. B. subtilis produces the proteolytic enzyme subtilisin. B. subtilis spores can survive the extreme heat during cooking. B. subtilis is responsible for causing ropiness — a sticky, stringy consistency caused by bacterial production of long-chain polysaccharides — in spoiled bread dough.'''

Reproduction
B. subtilis can divide symmetrically to make two daughter cells (binary fission), or asymmetrically, producing a single 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 process of sporulation the cells might become motile by producing flagella, and also take up DNA from the environment. Both these responses are viewed as attempts to seek out nutrients by going to a more favourable environment or by enabling the cell to use a new nutrient source if the DNA which is taken up contains a useable gene.

Chromosomal replication
B. subtilis is a model organism used to study bacterial chromosome replication. Replication of the single circular chromosome initiates at a single locus, the origin (oriC). Replication proceeds bidirectionally and two replication forks progress in clockwise and counterclockwise directions along the chromosome. Chromosome replication is completed when the forks reach the terminus region, which is positioned opposite to the origin on the chromosome map. The terminus region contains several short DNA sequences (Ter sites) that promote replication arrest. Specific proteins mediate all the steps in DNA replication. Comparison between the proteins involved in chromosomal DNA replication in B. subtilis and in Escherichia coli reveals 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.

Model organism
B. subtilis has proven highly amenable to genetic manipulation, and has 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 quickly in liquids. 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 bacterium.

Wild-type natural isolates of B. subtilis are difficult to work with compared to laboratory strains which have undergone domestication processes of mutagenesis and selection. These strains often have improved capabilities of transformation (uptake and integration of environmental DNA), growth and loss of abilities needed "in the wild", and while dozens of different strains fitting this description exist, the strain designated 168 is without doubt the most widely used.

Uses
B. subtilis is used as a soil inoculant in horticulture and agriculture. B. globigii, a closely related but phylogenetically distinct species was used as a biowarfare simulant during Project SHAD (aka Project 112).

Enzymes produced by B. subtilis and B. licheniformis are widely used as additives in laundry detergents.

Its other uses include:
 * A strain of B. subtilis formerly known as Bacillus natto is used in the commercial production of the Japanese food natto, as well as the similar Korean food cheonggukjang.
 * B. subtilis strain QST 713 (marketed as QST 713 or Serenade) has a natural fungicidal activity, and is employed as a biological control agent.
 * It was popular worldwide before the introduction of consumer antibiotics as an immunostimulatory agent to aid treatment of gastrointestinal and urinary tract diseases. It is still widely used in Western Europe and the Middle East as an alternative medicine
 * It can convert (decompose) some explosives into harmless compounds of nitrogen, carbon dioxide, and water.
 * Its surface binding properties play a role in safe radionuclide waste [e.g. thorium (IV) and plutonium (IV)] disposal.
 * Recombinant strains pBE2C1 and pBE2C1AB were used in production of polyhydroxyalkanoates (PHA), and malt waste can be used as their carbon source for lower cost PHA production.
 * It is used to produce amylase.
 * It is used to produce hyaluronic acid, which is useful in the joint-care sector in healthcare.
 * It may provide some benefit to saffron growers by speeding corm growth and increasing stigma biomass yield.

Genome
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.

Several non-coding RNAs have been characterized in the B. subtilis genome, including Bsr RNAs.

History
In 1835, the bacterium was originally named Vibrio subtilis by Christian Gottfried Ehrenberg, and renamed Bacillus subtilis by Ferdinand Cohn in 1872. Cultures of B. subtilis were used throughout the 1950s as an alternative medicine due to the immunostimulatory effects of its cell matter, which upon digestion has been found to significantly stimulate broad spectrum immune activity including activation of specific antibody IgM, IgG and IgA secretion and release of CpG dinucleotides inducing INF A/Y producing activity of leukocytes and cytokines important in the development of cytotoxicity towards tumor cells. It was marketed throughout America and Europe from 1946 as an immunostimulatory aid in the treatment of gut and urinary tract diseases such as Rotavirus and Shigella, but declined in popularity after the introduction of cheap consumer antibiotics, despite causing less chance of allergic reaction and significantly lower toxicity to normal gut flora.