Bacillus

GENUS: BACILLUS

Gram-positive, Aerobic or Facultative Endospore-forming Bacteria

INTRODUCTION:

Bacilli are rod-shaped, Gram-positive, sporulating, aerobes or facultative anaerobes. The term bacillus has been applied in a general sense to all cylindrical or rod like bacteria.  The cell wall is composed of teichoic and teichuronic acids. The largest species are about 2 μm (micrometres; 1 μm = 10⁻⁶ m) across by 7 μm long and frequently occur in chains. Widely found in soil and water. Most bacilli are saprophytes. Each bacterium creates only one spore, which is resistant to heat, cold, radiation, desiccation, and disinfectants. Bacilli exhibit an array of physiologic abilities that allow them to live in a wide range of habitats, including many extreme habitats such as desert sands, hot springs, and Arctic soils. Species in the genus Bacillus can be thermophilic, psychrophilic, acidophilic, alkaliphilic, halotolerant, or halophilic and are capable at growing at pH values, temperatures, and salt concentrations where few other organisms can survive. Bacilli are an extremely diverse group of bacteria that include both the causative agent of anthrax (Bacillus anthracis) as well as several species that synthesize important antibiotics.

Domain: Bacteria       Division: Firmicutes        Class: Bacilli

Order: Bacillales         Family: Bacillaceae         Genus: Bacillus.

General Habitat:

     The primary, general habitat for all bacilli is soil, but because of their endospores' resistance, and their ability to have long-term survival under bad conditions, they are ubiquitous (can be isolated from many needed sources for a long period of time).   

The soil, once considered their habitat, may simply serve as a reservoir. A growing number of studies show that Bacillus spores can be found in the intestinal tracts

of animals, raising the question of whether this could be where they live and grow. In this study, we have conducted the first evaluation of Bacillus spore formers in soil and in human faeces. Our aim is simply to determine the abundance of aerobic spore-formers. Our results show that soil carries approximately 106 spores/g while human faeces an average of up to 104 spores/g. The numbers of spores found in faeces, we reason, is too high to be accounted for principally by ingestion of food contaminated with spores from soil. This provides further evidence that Bacillus spore formers may have adapted to survival within the intestinal tract of insects and other animals that ingest them.

History of bacillus

In 1872, Ferdinand Cohn, a contemporary of Robert Koch, recognized and named the bacterium Bacillus (specie name subtilis). The organism is Gram-positive, capable of growth in the presence of oxygen, and forms a unique type of resting cell called an endospore. The organism represented what was to become a large and diverse genus of bacteria named Bacillus, in the Family Bacillaceae. 

Koch relied on Cohn's observations in his classic work (1876), the etiology of anthrax based on the life history of Bacillus anthracic, which provided the first proof that a specific microorganism could cause a specific disease.

The genus Bacillus was split into several families and genera of endospore-forming bacteria, justifiable on the basis of ssRNA analysis. In order to accommodate former members of the genus Bacillus, its title has been changed to "Gram-positive aerobic or facultative endospore-forming bacteria".

The unifying characteristic of these bacteria is that they are Gram-positive, form endospores, and grow in the presence of O₂. The trivial name assigned to them is aerobic spore formers.

BIOCHEMICAL ACTIVITIES OF BACILLUS

• Bacillus is catalase positive bacteria, because organisms that utilize citrate for energy produce alkaline compounds as by-products & they produce bubble on slant.
• Bacillus subtilis contains catalase KatA and MrgA, an enzyme that is responsible in the catalysis of hydrogen peroxide to water and oxygen, and superoxide dismutase.

·        Bacillus subtilis duplicates its single circular chromosome by initiating DNA replication at a single locus.

·        Many Bacillus species are able to secrete large quantities of enzymes. Bacillus amyloliquefaciens is the source of a natural antibiotic protein barnase (a ribonuclease), alpha amylase used in starch hydrolysis & give clear zone.

·        Bacillus can reduce nitrate into nitrite. Nitrite reductase activity was demonstrated in cell extracts prepared from both with benzyl viologen as an electron donor and nitrite as an electron acceptor.

·        Bacillus have the activity of gelatin hydrolysis. This showed that Bacillus have the ability to produce proteolytic exoenzyme of gelatinase, which can hydrolyzes gelatin into amino acids.

·        Some species of Bacillus can ferment glucose & lactose &produce gas as well like Bacillus polymyxa etc.

·        This genus is oxidase & urease negative.

·        Some species of Bacillus produce a lot of 2, 3-butanediol and ethyl alcohol instead of acids. These organisms are called butanediol fermenters. The production of these nonacid end products results in less lowering of the pH in methyl red Vogues- Proskauer media and, thus, the test is negative.

·        Bacillus species have the activity of gelatin hydrolysis. This is showed that B. subtilis have the ability to produce proteolytic exoenzyme of gelatinase, which can hydrolyzes gelatin into amino acids.

VARIOUS SPECIES OF BACILLUS

Bacillus anthracis is the etiologic agent of anthrax — a common disease of livestock and, occasionally, of humans — and the only obligate pathogen within the genus Bacillus. anthracis is a Gram-positive, endospore-forming, rod-shaped bacterium, with a width of 1-1.2µm and a length of 3-5µm It can be grown in an ordinary nutrient medium under aerobic or anaerobic conditions.

Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-

positive, catalase-positive bacterium. 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.

 Bacillus brevis, also known as Brevibacillus brevis is a Gram-positive aerobic spore-forming bacillus commonly found in soil, air, water, and decaying matter. It is rarely associated with infectious diseases. The antibiotics gramicidin and tyrocidine were first isolated from it.

Bacillus pumilus is a Gram-positive, aerobic, spore-forming bacillus commonly found in soil.

Bacillus licheniformis is a bacterium commonly found in the soil. It is found on bird feathers, especially chest and back plumage, and most often in ground-dwelling birds (like sparrows) and aquatic species (like ducks).

Other species of bacillus including: B. alcalophilus B. alvei B. aminovorans B. amyloliquefaciens B. aneurinolyticus B. aquaemaris B. atrophaeus B. boroniphilus B. caldolyticus B. centrosporus B. cereus B. circulans B. coagulans B. firmus B. flavothermus B. fusiformis B. globigii B. infernus B. larvae B. laterosporus B. lentus B. megaterium B. mesentericus B. polymyxa B. pseudoanthracis & others.

DISEASES CAUSED BY BACILLUS

• Bacillus anthracis causes anthrax in sheep and humans,
• Lactobacillus causes tooth decay and is also an ingredient in yogurt.
• Bacilli can cause tetanus (lockjaw) typhoid fever, tuberculosis, and diphtheria.