Bacillus Subtilis

Description & Signifigance

Originally named Vibrio subtilis in 1835, this organism was renamed Bacillus subtilis in 1872. Other names for this bacteria also include Bacillus uniflagellatus, Bacillus globigii, and Bacillus natto. Bacillus subtilis bacteria were one of the first bacteria to be studied. These bacteria are a good model for cellular development and differentiation.

Bacillus subtilis cells are rod-shaped, Gram-positive bacteria that are naturally found in soil and vegetation. Bacillus subtilis grow in the mesophilic temperature range. The optimal temperature is 25-35 degrees Celsius (Entrez Genome Project). Stress and starvation are common in this environment, therefore, Bacillus subtilis has evolved a set of strategies that allow survival under these harsh conditions. One strategy, for example, is the formation of stress-resistant endospores.

Genome Structure

Only one DNA molecule is present in these cells. Bacillus subtilis has one circular chromosome. The total size of all the DNA is 4,214,814 bp (4.2 Mbp). 4,100 genes code for proteins. 53% of the protein-coding genes are only seen once, while 25% of the genome relates to families of genes that have undergone gene duplication.

A great portion of the genome corresponds to carbon source applications 192 of the 4,100 genes are considered indispensable, and an additional 79 are thought to be essential. Most of the essential genes are involved in metabolism. Half of the essential genes are responsible for processing information, one-fifth of them are responsible for cell wall synthesis, cell division, and shape, and one-tenth of them were responsible for the energetics of the cell. The essential genes that code for functions that are not known are 4%. Bacillus subtilis bacteria are capable of secreting antibiotics in great numbers to the exterior of the cell. Five signal peptidase genes were found to be important for this secretion function. Many of Bacillus subtilis cells' genes are responsible for antibiotic synthesis.

Cell Structure and Metabolism

Bacillus subtilis are rod-shaped bacteria that are Gram-positive (Perez 2000). The cell wall is a rigid structure outside the cell. It is composed of peptidoglycan, which is a polymer of sugars and amino acids. The peptidoglycan that is found in bacteria is known as murein. Other constituents that extend from the murein are teichoic acids, lipoteichoic acids, and proteins. The cell wall forms the barrier between the environment and the bacterial cell. It is also responsible for maintaining the shape of the cell and withstanding the cell's high internal turgor pressure.

B. subtilis is capable of butanediol fermentation. It does not hydrolyze phospholipids nor casein; it does hydrolyze triglycerides. It produces citrate permease and cytochrome c.

Bacillus subtilis is a model organism for studying endospore formation in bacteria. Endospores in Bacillus subtilis bacteria are mostly formed in the tips of protuberances extending downward from liquid surface pellicles. Many strains produce spores with brown pigments. Depletion of carbon, nitrogen, or phosphorous causes the process of sporulation to begin, however, the process needs to start before the entire exhaustion of nutrients. Otherwise, the spore formation cannot be completed due to the fact that the nutrients are too low for the energy-requiring sporulation process. This allows the cells to avoid being stuck in a vulnerable position.

Application to Biotechnology

Bacillus organisms, isolated by soil sprinkle technique, are responsible for producing antibiotics. The most antibiotic activity was seen in Bacillus subtilis MH-4. The most optimal activity occurs at a temperature of 37 degrees Celsius and a basic pH of 8. Glycerol is the optimal carbon source and L-glutamic acid is the optimal source of nitrogen. The antibiotic bacitracin was determined to be effective on Gram-positive bacteria only. Other antibiotics that Bacillus subtilis form are polymyxin, difficidin, subtilin, and mycobacillin. Polymyxin is effective against Gram-negative bacteria, whereas difficidin has a broader spectrum.

Bacillus subtilis bacteria secrete enzymes, "such as amylase, protease, pullulanase, chitinase, xylanase, lipase, among others. These enzymes are produced commercially and this enzyme production represents about 60% of the commercially produced industrial enzymes" (Morikawa 2006).

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