Introduction

Bacillus subtilis is a Gram-positive, endospore-forming bacterium commonly found in soil, air, water, and decaying plant matter.
This rod-shaped, motile microorganism is a facultative aerobe, meaning it can survive in both oxygen-rich and oxygen-poor environments. Known for producing resistant endospores, B. subtilis can endure extreme heat, dehydration, and UV radiation.
Thanks to its well-studied genetics, easy cultivation, and rapid growth, B. subtilis is a model organism in microbiology research, especially for studies on sporulation, gene regulation, and cell differentiation.
Industrially, it is valuable for producing enzymes (e.g., amylases, proteases), antibiotics (e.g., bacitracin), and as a probiotic in agriculture and livestock feed.
Its GRAS (Generally Recognized as Safe) status makes it suitable for food and pharmaceutical applications.

Taxonomy of Bacillus subtilis

Phylum: Firmicutes
Class: Bacilli
Order: Bacillales
Family: Bacillaceae
Genus: Bacillus
Species: subtilis

Morphology of Bacillus subtilis

B. subtilis is a rod-shaped bacterium (2–6 μm long, <1 μm in diameter) with a rigid cell wall composed of thick peptidoglycan. This structure maintains its cylindrical shape and withstands high internal osmotic pressure.

Gram-positive– Thick peptidoglycan layer retains crystal violet stain.
DNA structure– Single, circular double-stranded chromosome.
Arrangement– Usually single rods but can appear in pairs, chains, or palisades.
Motility– Flagella enable swimming and gliding in liquids.
Biofilm formation– Rod shape facilitates aggregation into biofilms.

Properties

Gram reaction: Positive.
Shape: Rod-shaped.
Growth rate: Doubling time ~20 minutes under optimal conditions.
Temperature range: 30–35°C optimal, can grow 15–55°C.
Metabolism: Aerobic (facultative).
Special feature: Endospore formation under nutrient starvation.

Habitat

Bacillus is ubiquitous in a variety of environments worldwide, including soil, human, and animal bodies.
Most aerobic endospore-forming bacteria, such as Bacillus, are saprophytes that are dispersed in natural environments as spores. However, some may be found in living surfaces such as tissues and behave as opportunistic or obligate pathogens.
The primary habitat for subtilis is a variety of soils, including acidic to alkaline, cold to hot, and fertile to desert.
The kinds of strains residing in habitats are influenced by water content and deposits.
The presence of subtilis in various habitats results from the dispersal of bacterial spores as aerosols. Furthermore, B. subtilis can thrive at a diverse temperature range of 15°C to 55°C.
Some strains of B. subtilis are ubiquitous contaminants in food, water, and the natural, residential, industrial, and hospital environments.
The endospores of B. subtilis are resistant to physical and chemical factors such as heat, disinfectants, antibiotics, and hazardous chemicals.
Bacterial spores can also be present in large quantities in dried foods such as spices, milk powder, and other items.
B. subtilis are heterotrophic bacteria that have been isolated from environments with varying nutrient availability and environmental conditions.

Diseases Caused by Bacillus subtilis

1. Bacteremia (bloodstream infection)

Bacillus subtilis may sometimes cause bacteremia, particularly in hospitalized or immune-compromised individuals, such as cancer patients, transplant recipients, and those with catheters. Bacteria can get into the bloodstream via infected intravenous lines or medical devices.
Symptoms: It can include fever, chills, rapid heartbeat, and low blood pressure. Although uncommon, it can cause sepsis if left untreated, which is potentially fatal. Antibiotic therapy is generally successful.
Diagnosis: blood culture and Gram staining, which reveal Gram-positive rods that are confirmed using automated identification systems.

2. Endophthalmitis (Eye Infection)

Bacillus subtilis has rarely been implicated in post-surgical or trauma-related endophthalmitis, a serious inflammation of the eye’s internal layers. This happens when bacteria enter the eye during an injury or surgery.
Symptoms: may include eye pain, redness, blurred vision, and swelling. It is treated as an emergency situation and could result in permanent vision loss if not promptly treated with intravitreal antibiotics and possibly surgery (vitrectomy).
Diagnosis: culturing vitreous or aqueous humor, microscopic analysis, and PCR testing, as well as a slit lamp eye exam.

Industrial application of chemicals produced by Bacillus Subtilis

The industrial use of B. subtilis has grown swiftly over the previous few decades, and it has become the predominant microbial cell factory for a variety of industrial goods such as enzymes, heterologous proteins, antibiotics, vitamins, and amino acids. Chemicals generated by B. subtilis are also important in a variety of sectors, including food, feed, cosmetics, chemicals, and pharmaceuticals.

Bacillus Subtilis produces enzymes

B. subtilis has emerged as an excellent expression host for the manufacture of numerous industrial enzymes due to its fast proliferation on cheap substrates, strong protein secretion capability, non-pathogenicity, and advantageous downstream processing. B. subtilis produces 50% of the total enzyme market.
Many enzymes have been effectively produced in B. subtilis, including amylases, xylanases, lichenase, β-galactosidase, cellulases, alkaline serine proteases, and others.
These enzymes are vital in the food, feed, detergent, textile, leather, paper, and pharmaceutical sectors.
Because of its GRAS designation, B. subtilis proteases may be utilized in a variety of food applications, including soybean hydrolysate preparation, meat tenderization, casein hydrolysate preparation, milk coagulation, and food waste management.

Alpha amylase

Alpha-amylase catalyzes the hydrolysis of α1, 4-glucosidic bonds, resulting in the release of glucose from starch.
It is extensively utilized in the textile and paper industries, and B. subtilis is a predominant host for the manufacturing of heterologous αamylases.

Xylanases

Xylanases are enzymes that hydrolyze the β1, 4 glycosidic linkages of xylans, generating oligosaccharides and disaccharides that include reducing sugars and xylose.
They have considerable application value in biotechnology and can be employed to alter lignocellulosic materials.
Xylanases are utilized in animal feed production, the paper and textile industries, and biofuel generation.
Commercial xylanases are mostly manufactured in B. subtilis.

Lichenase

Lichenase a mixed-linked β-glucan (MLG) endohydrolase found in both microorganisms and plants has attracted interest in biofuel production studies.
However, due to its low thermal stability, it is unsuitable for biocatalytic biomass conversion.

Biochemical Characteristics of Bacillus subtilis

Bacillus subtilis is a Gram-positive, rod-shaped, endospore-forming bacterium widely studied for its metabolic versatility and industrial importance. Its biochemical profile helps differentiate it from other Bacillus species and aids in laboratory identification.

Test	Result
Gram Staining	Grams-Positive
Cell Shape	Rod-shaped
Motility	Motile (peritrichous flagella)
Spore Formation	Yes (oval, central or subterminal spores)
Oxygen Requirement	Facultative anaerobe (can grow aerobically or anaerobically)
Catalase Test	Positive
Oxidase Test	Positive
Indole Test	Negative
Glucose Fermentation	Positive (acid only)
Sucrose Fermentation	Positive
Lactose Fermentation	Variable
Mannitol Fermentation	Positive
Arabinose Fermentation	Positive
Xylose Fermentation	Positive
Glycerol Utilization	Positive
Amylase (Starch Hydrolysis)	Positive
Casein Hydrolysis	Positive
Gelatin Liquefaction	Positive
Lipase	Positive
Urease	Negative
Nitrate Reduction	Positive
β-galactosidase	Variable
Salt Tolerance (up to 7% NaCl)	Positive

Industrial Applications of Bacillus subtilis

Enzyme Production

B. subtilis produces 50% of commercially used enzymes due to its high secretion ability, safety, and rapid growth.
Key enzymes include:

Alpha-amylase: Breaks down starch for food, textile, and paper industries
Xylanase: Used in biofuel production, paper processing, and animal feed
Lichenase: Involved in biofuel research (limited by thermal stability)

Antibiotic & Chemical Production

Produces bacitracin, surfactin, subtilin, and other antimicrobial peptides with applications in:

Food preservation.
Agriculture (plant disease control).
Biomedical engineering.

Applications in Agriculture & Medicine

Agriculture

Used as a probiotic in animal feed to improve digestion and gut health
Controls plant pathogens through antibiotic peptide secretion
Enhances nutrient absorption in livestock and aquaculture species

Medicine & Biotechnology

Produces bioactive compounds with antimicrobial properties
Used in drug delivery research and as a model organism for genetic studies

Summary Table – Bacillus subtilis Overview

Feature	Description
Gram Stain	Positive
Shape	Rod-shaped
Size	2–6 μm length
Motility	Yes
Spore Formation	Yes
Habitat	Soil, water, air, food
Industrial Use	Enzymes, antibiotics, probiotics
Pathogenicity	Low (opportunistic in rare cases)

Frequently Asked Questions (FAQ) on Bacillus subtilis

Q1: What is Bacillus subtilis?
Bacillus subtilis is a Gram-positive, rod-shaped, endospore-forming bacterium commonly found in soil, air, water, and decomposing organic matter. It is widely used in microbiology research and industrial applications due to its safety and versatility.
Q2: Is Bacillus subtilis harmful to humans?
In most cases, B. subtilis is considered non-pathogenic and safe (GRAS – Generally Recognized as Safe). However, in rare cases, it can cause opportunistic infections like bacteremia or endophthalmitis, mainly in immunocompromised individuals.
Q3: Where can Bacillus subtilis be found?
It is found worldwide in diverse environments, including soil, water, air, plant surfaces, and even as a contaminant in food and industrial settings. Its spores are highly resistant and can survive extreme conditions.
Q4: What diseases can Bacillus subtilis cause?
Though rare, B. subtilis can cause bacteremia (blood infection) and endophthalmitis (eye infection), particularly in people with weakened immune systems or after surgical procedures.
Q5: Why is Bacillus subtilis important in biotechnology?
B. subtilis is a preferred microbial cell factory for producing enzymes, antibiotics, and other industrial products. It secretes large amounts of proteins, grows quickly, and can thrive on inexpensive substrates.
Q6: What enzymes are produced by Bacillus subtilis?
It produces alpha-amylase, proteases, xylanases, lichenase, and other industrially important enzymes used in food processing, textiles, detergents, paper production, and pharmaceuticals.
Q7: How is Bacillus subtilis used in agriculture?
It is used as a probiotic in livestock feed to improve gut health, aid digestion, and control harmful bacteria. It also acts as a biocontrol agent against plant pathogens.
Q8: Can Bacillus subtilis survive extreme conditions?
Yes. Its endospores are resistant to heat, UV radiation, dehydration, and many chemicals, allowing it to persist in harsh environments.
Q9: What is the optimal growth temperature for Bacillus subtilis?
The optimal growth temperature is between 30–35°C, though it can grow within a broader range of 15–55°C.
Q10: Is Bacillus subtilis used in medicine?
Yes. It produces antimicrobial peptides like surfactin and bacitracin, which have potential applications in pharmaceuticals, food preservation, and infection control.

Reference and Sources

https://en.wikipedia.org/wiki/Bacillus

Bacillus subtilis– Morphology, Habitat, Diseases & Industrial Applications