Random Selection Of Microorganism ; 9) Bacillus Megaterium ( Rod Shaped Bacteria Arranged in Chains)

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1)Bacillus megaterium :

Bacillus megaterium is a rod-like, Gram-positive, mainly aerobic spore forming bacterium found in widely diverse habitats.

With a cell length of up to 4 µm and a diameter of 1.5 µm, B. megaterium is amongst the biggest known bacteria.

The cells often occur in pairs and chains,where the cells are joined together by polysaccharides on the cell walls.

In the 1960s, prior to the development of Bacillus subtilis, B. megaterium was the main model organism among Gram-positive bacteria for intensive studies on biochemistry, sporulation and bacteriophages. 

Recently, its popularity has started increasing in the field of biotechnology for its recombinant protein production capacity.

2) Classifications :

Domain       :   Bacteria 

Phylum       :    Firmicutes

Class          :     Bacilli

Order           :    Bacillales

Family         :    Bacillaceae 

Genus         :     Bacillus 

Species      :      Bacillus megaterium

Bacillus megaterium cells stained                  with Sudan Black B and safranin.

Introduction :  

Bacillus megaterium is a gram positive, endospore forming, rod shaped bacteria.

It is considered aerobic. It is found in soil and considered a saprophyte.

Bacillus megaterium is latin for the big beast because it is an extremely large bacteria, it is about 100 times as large as E. coli. 

Due to its immense size, about 60 micrometers cubed, B. megaterium has been used to study structure, protein localization and membranes of bacteria since the 1950’s. 

Most notably, B. megaterium is the organism that was used by Lwoff and Guttman in the studies that discovered lysogeny.

3) Ecology : 

a) Ocurrance :

B. megaterium is ubiquitous in the environment around us. In addition to being a common soil bacterium and an endophyte, 

it can be found in various foods (including honey and bee pollen, in which most microorganisms do not grow) and on a variety of surfaces, including clinical specimens, leather, paper, stone etc. 

It has also been isolated from cow feces, emperor moth caterpillars and greater wax moth frass.

The method of described in can be used to isolate strains of B. megaterium from the soil. 

b) islolation : 

The procedure starts with plating 0.1 ml of dilutions of heat-treated soil suspensions on glucose mineral base agar & adjust pH 7

Plates are incubated at 30 °C. 

White, round, smooth and shiny colonies 1–3 mm in diameter may develop on the nitrate (KNO₃) medium in 36–48 hours. 

However, not all strains can use nitrate, therefore the recommendation to use the ammonium ((NH₄)₂SO₄) medium in parallel. 

Colonies are detected by their appearance and suspects should be observed microscopically for the typically large cells of this species.

4) Cell Structure : 

Bacillus megaterium is a gram positive, endospore forming, rod shaped bacteria. It is considered aerobic. ... Due to its immense size, about 60 micrometers clubed, B. megaterium has been used to study structure, protein localization and membranes of bacteria since the 1950's.

The pattern of cross-linking in the peptidoglycan of Bacillus megaterium has been studied by the pulsed addition of radiolabeled diaminopimelic acid. 

The distribution of label in muropeptides, generated by digestion with Chalaropsis muramidase and separated by high-performance liquid chromatography, stabilized after 0.15 of a generation time. 

The proportion of label in the acceptor and donor positions of isolated muropeptide dimers stabilized over the same period of time. The results have led to the formulation a new model for the assembly of peptidoglycan into the cylindrical wall of B. megaterium by a monomer addition process. 

Single nascent glycan peptide strands form cross-linkages only with material at the inner surface of the wall. Maturation is a direct consequence of subsequent incorporation of further new glycan peptide strands, and there is no secondary cross-linking process. 

The initial distribution of muropeptides is constant. It follows that the final pattern of cross-linking in the wall is determined solely by, and can be forecast from, this repetitive pattern of incorporation. 

In a modified form, this model can also be applied to assembly of cell walls in rod-shaped gram-negative bacteria.

5) Metabolism :  

The steroid hydroxylase system in Bacillus megaterium that hydroxylates 3-oxo-Δ⁴-steroids primarily in position 15β has been resolved into an NADPH-specific FMN-containing reductase (megaredoxin reductase), an iron-sulphur protein (megaredoxin) and cytochrome P-450_meg. 

Megaredoxin reductase can be replaced by rabbit liver NADPH-cytochrome P-450 reductase. In reactions supported by oxygen-donating agents as NaIO₄ or iodosobenzene, hydroxylation occurs in both position 15α and 15β. 

By Using hydrophobic chromatography cytochrome P-450_meg has been purified to 20% homogeneity. This protein has an isoelectric point of 4.9 and a molecular weight of approximately 37 000 D. Phosphatidylcholine stimulated NaIO₄-supported, P-450_meg-catalyzed hydroxylation reactions by a factor of two.

6) Pathogenicity : 

Bacillus represents a genus of ubiquitous gram-positive bacteria. The species are used in many medical, pharmaceutical, agricultural, and industrial processes, including those for making antibiotics and insecticides .

 Even the anthrax toxin is being evaluated as a choice for tumor cell surface targeting in chemoresistant neoplasms .

Although most species are harmless, two are medically significant: Bacillus anthracis and B. cereus. B. anthracis causes anthrax in its cutaneous, pulmonary (inhalational), and intestinal forms. 

B. cereus causes two distinct food poisoning syndromes, a rapid-onset emetic syndrome characterized by nausea and vomiting and a slower onset diarrheal syndrome.

Bacillus are often isolated on blood culture and usually represent blood culture contamination. For example, Bacillus species pseudobacteremia has been traced to contaminated gloves used in collection of blood from patients .

In immunocompromised hosts, a blood culture growing Bacillus species should be evaluated carefully. Rarely, these species cause important clinical diseases such as bacteremia, sepsis, meningitis, pneumonia, empyema, ophthalmitis, osteomyelitis, endocarditis, soft tissue infection, and intravascular catheter-acquired sepsis.

Pseudotumour of the lung has been reported as the cause of infection with B. sphaericus . Endocarditis has been reported to be caused by B. subtilis . 

An outbreak of Bacillus species in a cancer hospital in Brazil was reported and was strongly associated with use of calcium gluconate solution and central venous lines. The outbreak was controlled by stopping use of the implicated calcium gluconate vials.