What is Bacillus subtilis Used For?

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Bacillus subtilis is a plant-growth-promoting rhizobacterium that also impacts biotic stress. It is a useful cell factor for agriculture, industry, biomaterials, and medicine. Let’s find out more uses of Bacillus subtilis!

What is Bacillus subtilis
Bacillus subtilis

What is Bacillus subtilis Used For?

Bacillus subtilis is a tremendously useful cell factor for agriculture, industry, biomaterials, and medicine. Because its genetics is well-characterized, B. subtilis is the key Gram-positive bacterium for studies of metabolism and physiology. Because it has a highly adaptable metabolism and it is very efficient at producing proteins, B. subtilis is a highly desirable cell factor for the production of enzymes, antimicrobials, and chemicals for bioremediation, agriculture, industry, and medicine. 

B. subtilis secretes a variety of enzymes that allow it to use a variety of substrates provided by a constantly changing environment. As a result, it can be mass produced in expensive media. B. subtilis has a fermentation cycle of just 48 hours, compared to the 180 hours required by Saccharomyces cerevisiae. Unlike Escherichia coli, B. subtilis has a single cell membrane, enhancing protein and enzyme secretion, simplifying downstream processing, and reducing production costs. Moreover, it is generally recognized as safe (GRAS).

Over the last 30 years, many tools for the genetic modification of B. subtilis have been developed. Artificial promoter and ribosome binding site (RBS) libraries empower the creation of heterologous proteins. As a result, this bacterium is a versatile cell factory, producing acetoin, hyaluronan, inositol, vitamins, and other chemicals. It is also an ideal multifunctional probiotic, improving absorption of essential nutrients and fighting pathogenic species.

This bacterium also produces complex biofilms, useful as biomaterials and producing antibiotics and lysozyme for medical applications.

Representative chemicals produced by genetically modified proprietary strains of B. subtilis  include amorphadiene, chondroitin, heparosan, isobutanol, menaquinone-7, riboflavin, and poly-γ-glutamic acid. We'll discuss some of the high-value products of B. subtilis in more detail.

Vitamin Production with B. subtilis 

Mutant libraries and genetic engineering have provided multiple strains of B. subtilis useful for producing vitamins B1, B2, B5, B6, and B7. B. subtilis is used for producing vitamin B2 (riboflavin) on an industrial scale. Riboflavin, of course, is found in many over-the-counter B-vitamin supplements. It is also used as a growth enhancer in animal feeds. In human health, it has known antioxidants, immunostimulant, and anticancer effects.

Metabolic engineering strategies utilizing the riboflavin metabolic pathway of B. subtilis usually optimize central carbon metabolism. They induce overexpression and deregulation of riboflavin and purine biosynthesis pathways, and block the synthesis of byproducts. Redirecting carbon flux from the EMP (Embden-Meyerhof-Parnas) pathway to the PPP (pentose phosphate pathway) increases expression of purine biosynthesis genes (pur operon), resulting in greater GTP production. As a result, B. subtilis produces extraordinarily high yields of riboflavin in the bioreactor. Recent developments in bioengineering B. subtilis enable the introduction of heat shock proteins that improve osmotic tolerance and heat tolerance of the bacterium, allowing it to be fermented at a higher temperature, reducing production time and increasing yields.

B. subtilis can also produce menaquinone-7 (MK-7), a K vitamin essential for the regulation of calcium in bone. MK-7 is also an essential component of the microbial membrane, where it plays an important role in oxidative phosphorylation and electron transfer. Recent advances in engineering the bacterium have introduced a knockout gene that greatly increases yield.


Enzymes Produced by B. subtilis

Lack of pathogenicity, strong ability to secrete proteins, strong growth on inexpensive substrates, and ease of downstream processing make B. subtilis a superior expression host for the production of a number of industrially important enzymes. Although there are no authoritative statistics, it is likely that B. subtilis is used to produce the majority of recombinant enzyme products on the market today. 

B. subtilis is used to express many industrially important enzymes, including alkaline serine proteases, amylases, β-galactosidase, cellulases, lichenase, xylanases, and many more. These enzymes have important applications in the feed, food, detergent, leather, paper, pharmaceutical, and textile industries. GRAS status allows the use of this bacterium in many important food applications, such as casein hydrolysate preparation, milk coagulation, meat tenderization, and soybean hydrolysate preparation, as well as the treatment of food waste.

Alpha-amylase (EC 3.2.1.1) accelerates the cleavage of α-1,4-glucosidic bonds, liberating glucose from starch. It is very useful in the paper and textile industries. Genetically engineered B. subtilis serves as the major host for the production of heterologous α-amylases.

Lichenase (EC. 3.2.1.73) appears in plants and microorganisms. It is a thermally unstable mixed linked β-glucan (MLG) endo-hydrolase, not suitable for biocatalytic conversion of biomass due to its thermal instability. However, B. subtilis can be bioengineered to create enzymate trimers that are predictably bioreactive.

Xylanases (EC. 3.2.1.8) catalyze the hydrolysis of β-1,4 glycosidic xylan linkages, liberating disaccharides and oligosaccharides that contain reducing sugars and xylose. They are used in biofuel production, animal feed manufacturing, and the paper and textile industries. Incubating B. subtilis with Kluyveromyces marxianus  increases the production of xylanases four-fold over the use of either microbe alone.


Applications of B. subtilis in agriculture, biomaterials and medicine

B. subtilis is more than merely Generally Regarded as Safe (GRAS). As a microbial additive to animal feed, it improves intestinal function in livestock. It prevents disease and promotes growth. B. subtilis can be produced in the form of endospores, which enter the small intestine quickly and produce amylases and lipases that break down the complex carbohydrates in hay, fodder, and other animal feed. 

B. subtilis improves the digestibility of animal feed by modifying the microbial landscape of the gut, producing polypeptides antagonistic to pathogenic organisms. Since it is an aerobic organism, it consumes oxygen in the intestine, creating a more favorable environment for anaerobic probiotic bacteria. 

Antimicrobial peptides produced by B. subtilis show promise as therapeutic tools. They kill a broad spectrum of pathogens quickly. With an ever-increasing problem of antibiotic resistance due to overuse of antibiotics, these antimicrobial peptides show great promise in animal health.  Adding B. subtilis spores to chicken feed increases egg production and the strength of eggshells. Adding B. subtilis spores to feed for dairy cattle increases milk production and the percentage of protein in the milk.

B. subtilis forms complex and robust biofilms. These biological polymers can be fabricated into useful microstructures by 3-D printing. This artificial living material has programmability and self-repair properties.

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