Bacillus is a genus of Gram-positive, rod-shaped, bacteria and a member of the phylum Firmicutes.
Bacillus species can be obligate aerobes, or facultative anaerobes.
They will test positive for the enzyme catalase when there has been oxygen used or present.
Ubiquitous in nature, Bacillus includes both free-living and parasitic pathogenic species.
Under stressful environmental conditions, the bacteria can produce oval endospores that
are not true spores but which the bacteria can reduce themselves to and remain in a dormant
state for very long periods.
These characteristics originally defined the genus, but not all such species are closely
related, and many have been moved to other genera of Firmicutes.
Many species of Bacillus can produce copious amounts of enzymes which are made use of in
different industries.
Some Bacillus species can form intracellular inclusions of polyhydroxyalkanoates under
certain adverse environmental conditions, as in a lack of elements such as phosphorus,
nitrogen, or oxygen combined with an excessive supply of carbon sources.
B.subtilis has proved a valuable model for research.
Other species of Bacillus are important pathogens, causing anthrax and food poisoning.
Industrial significance Many Bacillus species are able to secrete
large quantities of enzymes.
Bacillus amyloliquefaciens is the source of a natural antibiotic protein barnase, alpha
amylase used in starch hydrolysis, the protease subtilisin used with detergents, and the BamH1
restriction enzyme used in DNA research.
A portion of the Bacillus thuringiensis genome was incorporated into corn crops.
The resulting GMOs are therefore resistant to some insect pests.
Use as model organism Bacillus subtilis is one of the best understood
prokaryotes, in terms of molecular biology and cell biology.
Its superb genetic amenability and relatively large size have provided the powerful tools
required to investigate a bacterium from all possible aspects.
Recent improvements in fluorescence microscopy techniques have provided novel and amazing
insight into the dynamic structure of a single cell organism.
Research on Bacillus subtilis has been at the forefront of bacterial molecular biology
and cytology, and the organism is a model for differentiation, gene/protein regulation,
and cell cycle events in bacteria.
Clinical significance Two Bacillus species are considered medically
significant: B. anthracis, which causes anthrax, and B. cereus, which causes food poisoning
similar to that caused by Staphylococcus.
A third species, B. thuringiensis, is an important insect pathogen, and is sometimes used to
control insect pests.
The type species is B. subtilis, an important model organism.
It is also a notable food spoiler, causing ropiness in bread and related food.
Some environmental and commercial strains of B. coagulans may play a role in food spoilage
of highly acidic, tomato-based products.
An easy way to isolate Bacillus is by placing nonsterile soil in a test tube with water,
shaking, placing in melted mannitol salt agar, and incubating at room temperature for at
least a day.
Colonies are usually large, spreading, and irregularly shaped.
Under the microscope, the Bacillus cells appear as rods, and a substantial portion of the
cells usually contain oval endospores at one end, making it bulge.
Cell wall The cell wall of Bacillus is a structure on
the outside of the cell that forms the second barrier between the bacterium and the environment,
and at the same time maintains the rod shape and withstands the pressure generated by the
cell's turgor.
The cell wall is composed of teichoic and teichuronic acids.
B. subtilis is the first bacterium for which the role of an actin-like cytoskeleton in
cell shape determination and peptidoglycan synthesis was identified, and for which the
entire set of peptidoglycan-synthesizing enzymes was localised.
The role of the cytoskeleton in shape generation and maintenance is important.
Phylogeny The genus Bacillus was named in 1835 by Christian
Gottfried Ehrenberg, to contain rod-shaped bacteria.
He had seven years earlier named the genus Bacterium.
Bacillus was later amended by Ferdinand Cohn to further describe them as spore-forming,
Gram-positive, aerobic or facultatively anaerobic bacteria.
Like other genera associated with the early history of microbiology, such as Pseudomonas
and Vibrio, the 266 species of Bacillus are ubiquitous.The genus has a very large ribosomal
16S diversity and is environmentally diverse.
Several studies have tried to reconstruct the phylogeny of the genus.
The Bacillus-specific study with the most diversity covered is by Xu and Cote using
16S and the ITS regions, where they divide the genus into 10 groups, which includes the
nested genera Paenibacillus, Brevibacillus, Geobacillus, Marinibacillus and Virgibacillus.
However, the tree [3] constructed by the living tree project, a collaboration between ARB-Silva
and LPSN where a 16S tree of all validated species was constructed, the genus Bacillus
contains a very large number of nested taxa and majorly in both 16S and 23S it is paraphyletic
to Lactobacillales, due to Bacillus coahuilensis and others.
A gene concatenation study found similar results to Xu and Cote, but with a much more limited
number of species in terms of groups, but used Listeria as an outgroup, so in light
of the ARB tree, it may be "inside-out".
One clade, formed by B. anthracis, B. cereus, B. mycoides, B. pseudomycoides, B. thuringiensis,
and B. weihenstephanensis under current classification standards, should be a single species, but
due to medical reasons, they are considered separate species, an issue also present for
four species of Shigella and Escherichia coli.
See also Paenibacillus and Virgibacillus are genera
of bacteria that were formerly included in Bacillus
References
External links Bacillus genomes and related information at
PATRIC, a Bioinformatics Resource Center funded by NIAID